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Case Studies
Case Studies

Case Studies (329)

Saturday, 10 November 2012 14:39

Hartbeespoort Dam, South Africa

Written by Reinette (Oonsie) Biggs

Hartbeespoort Dam, South Africa

Main Contributors:

Reinette (Oonsie) Biggs

Other Contributors:

Summary

Hartbeespoort Dam is a reservoir in the North West Province of South Africa Coordinates. The dam was originally designed for irrigation which is still its primary use. Hartbeespoort Dam has been renowned for its poor water quality since the mid twentieth century (Allanson & Gieskes 1961). The Dam suffers severe eutrophication, resulting from high concentrations of phosphates and nitrates in the Crocodile River, the major inflow. The primary pollution sources are industrial and domestic effluent from Gauteng . The extreme level of eutrophication is evident in the excessive growth of microscopic algae and cyanobacteria, and macrophytes such as water hyacinth (Eichhornia crassipes). The South African Department of Water Affairs and Forestry launched the Harties metsi a me (English: Harties, My Water) programme to try to find solutions to the water quality problems.

Type of regime shift

Ecosystem type

  • Freshwater lakes & rivers

Land uses

  • Urban
  • Large-scale commercial crop cultivation
  • Extensive livestock production (natural rangelands)
  • Tourism

Spatial scale of the case study

  • Local/landscape (e.g. lake, catchment, community)

Continent or Ocean

  • Africa

Region

  • Northwest Province

Countries

  • South Africa

Locate with Google Map

Key References

  1. Allanson BR, Gieskes JMTM. 1961. Investigations into the ecology of polluted inland waters in the Transvaal, Part II: An introduction to the limnology of Hartbeespoort Dam with special reference to the effect of industrial and domestic pollution. Hydrobiologia, 18(1-2): 77-94.
  2. Harding WR, Thornton JA, Steyn G, Panuska J, Morrison IR. 2004. Hartbeespoort Dam Remediation Project (Phase 1) Action Plan Final Report (Volume II). North West Province DACE. Available from: http://www.dwa.gov.za/harties/
  3. Van Ginkel CE, Silberbauer MJ. 2007. Temporal trends in total phosphorus, temperature, oxygen, chlorophyll a and phytoplankton populations in Hartbeespoort Dam and Roodeplaat Dam, South Africa, between 1980 and 2000. African Journal of Aquatic Science 32 (1): 63-70.

Citation

Reinette (Oonsie) Biggs. Hartbeespoort Dam, South Africa. In: Regime Shifts Database, www.regimeshifts.org. Last revised 2012-11-10 14:55:35 GMT.
Saturday, 20 October 2012 17:12

Goulburn-Broken Catchment, Australia

Written by Reinette (Oonsie) Biggs

Goulburn-Broken Catchment, Australia

Main Contributors:

Reinette (Oonsie) Biggs

Other Contributors:

Summary

Around 85% of the native woodland and forest cover has been removed from the mid catchment of the Goulburn-Broken, and 98% from the lower catchment (GBCMA 2003). Anderies et al. (2006b) estimate that the cover of woody vegetation was reduced to below the threshold level needed to maintain the water table below the surface about a decade after clearing began. This threshold is estimated at about 80% vegetation cover in the mid catchment (groundwater in the upper catchment appears not to be connected to water tables in the mid and lower catchment). As water tables rise in response to the reduced vegetation cover, there is a critical threshold at around 2 m below the surface (depending on soil texture). When the water table rises above this, capillary action draws water to the surface. The height of the water table determines the area salinized because of topographic variation, so area salinized and water-table depth are treated as a single threshold. Because of a strong hysteresis effect (tree roots do not function well in saturated soil, so it takes more trees than in unsaturated soil to achieve the same amount of transpiration), more than 80% of the catchment needs to be revegetated to change the trajectory of the system such that the equilibrium water-table depth is below the root zone. As this would affect large areas of dryland farms, pumping is needed in addition to revegetation—the less revegetation, the more pumping (see Anderies et al. 2006b). A constraint is the large volumes of saline water produced. Almost twice as much saline water needs to be pumped if there is no revegetation, which would violate the current salt discharge cap. Revegetation and pumping are both costly. Extracted from Walker et al 2009.

Type of regime shift

Ecosystem type

  • Agro-ecosystems

Land uses

  • Large-scale commercial crop cultivation
  • Intensive livestock production (eg feedlots, dairies)

Spatial scale of the case study

  • Local/landscape (e.g. lake, catchment, community)

Continent or Ocean

  • Australia & New Zealand

Region

  • Murray-Darling Basin

Countries

  • Australia

Locate with Google Map

Key References

  1. Walker, B. H., N. Abel, J. M. Anderies, and P. Ryan. 2009. Resilience, adaptability, and transformability in the Goulburn-Broken Catchment, Australia. Ecology and Society 14(1): 12. [online] URL: http://www.ecologyandsociety.org/vol14/iss1/art12/

Citation

Reinette (Oonsie) Biggs. Goulburn-Broken Catchment, Australia. In: Regime Shifts Database, www.regimeshifts.org. Last revised 2012-11-10 14:25:51 GMT.

Uruguay - Mixed ranching to intensive crop production

Main Contributors:

Lisa Deutsch, Ylva Ran, Matilda Baraibar

Other Contributors:

Reinette (Oonsie) Biggs

Summary

Uruguay has a long tradition of extensive sheep and cattle livestock husbandry for subsistence and export as the dominant livelihood strategy. Since the 1970s the system was characterized by two types of livestock production: 1) mixed crop production in rotation with pastures was practiced in the western Litoral and 2) pastoral grazing based on natural grasslands with low external inputs and low-stocking density on poor, erosive soils in the rest of the country. The Uruguayan agricultural system was transformed into a new regime in about 2002, where a new productive system of continuous cultivation of soybeans with other crops emerged. The change was driven by several external forces, starting with an increased demand for animal products, mainly in China. This increased demand for animal feed crops for Asian domestic production contributed to increasing global soybean prices. When farmers showed profitable margins, soybeans became a lucrative option, which in turn drove a huge increase in Uruguayan land prices. This negatively affected economic margins in extensive livestock and intensive soy production became more economically attractive. The abrupt shift from ranching to cropping was catalyzed by a mass infusion of capital and technology from Argentina. Economic crisis in Argentina led actors with capital and knowledge and experience of the new agricultural technology package for no-till soybean production to enter an equally financially distressed Uruguay. The combination of advantageous economic margins, ecologically appropriate technology and necessary capital for this capital intensive production system combined to overwhelm previous Uruguayan resistance (strong cultural identity) to changing farming systems from ranchers to crop farmers in the Litoral region. Within only a few years, large-scale expansion of crop cultivations further affected the livestock sector as the most productive grazing areas were taken for crop production. Since economic margins for crop production were so much higher, the livestock sector lost producers and lands to crop production. Owners who did change farming systems left Litoral or went out of business. Most traditional sharecroppers lost access to land and many became service providers. One of the major ecological consequences of the adopted system is that continuous cropping degrades soil productivity due to decreased soil organic matter and increased risk of erosion. The government has taken steps to mitigate soil degradation by enforcing the existing Soil Law. However, soil degradation has not been stopped only slowed.

Type of regime shift

  • Extensive ranching to crop production

Ecosystem type

  • Grasslands
  • Agro-ecosystems

Land uses

  • Small-scale subsistence crop cultivation
  • Large-scale commercial crop cultivation
  • Intensive livestock production (eg feedlots, dairies)
  • Extensive livestock production (natural rangelands)

Spatial scale of the case study

  • Local/landscape (e.g. lake, catchment, community)

Continent or Ocean

  • South America

Region

  • Litoral – western Uruguay

Countries

  • Uruguay

Locate with Google Map

Key References

  1. Bot, A., and J. Benites. 2005. The importance of soil organic matter. FAO Soils Bulletin. Rome.
  2. Deutsch, L., M. Falkenmark, L. Gordon, J. Rockström, and C. Folke. 2010. Water-mediated ecological consequences of intensification and expansion of livestock production. Pages 97u2013111 in H. Steinfeld, H. A. Money, F. Schneider, and L. E. Neville, editors. Livestock in a Changing Landscape, Volume 1: Drivers, Consequences and Responses. Island Press, Wallingford.
  3. Dogliotti, S. 2003. Exploring options for sustainable development of vegetable farms in South Uruguay. Dissertation. Wageningen University.
  4. FAOSTAT. 2012. FAOSTAT. Retrieved from http://faostat.fao.org/.
  5. García-Préchac, F., and A. Duran. 2001. Estimating Soil Productivity Loss Due to Erosion in Uruguay in Terms of Beef and Wool Production on Natural Pastures u2020. Pages 40u201345 in D. E. Stott, R. H. Mohtar, and G. C. Steinhardt, editors. Sustaining the Global Farm. Purdue University and the USDA-ARS National Soil Erosion Research Laboratory.
  6. Garcia-Préchac, F., O. Ernst, G. Siri-Prieto, and J. A. Terra. 2004. Integrating no-till into crop-pasture rotations in Uruguay. Soil and Tillage Research 77:1u201313. doi: 10.1016/j.still.2003.12.002.
  7. MGAP. 2010. Anuario Estadistico Agropecuario 2010. Montevideo.

Citation

Lisa Deutsch, Ylva Ran, Matilda Baraibar, Reinette (Oonsie) Biggs. Uruguay - Mixed ranching to intensive crop production. In: Regime Shifts Database, www.regimeshifts.org. Last revised 2012-11-13 09:34:19 GMT.
Tuesday, 20 March 2012 09:06

Lake Victoria

Written by Susanne

Lake Victoria

Main Contributors:

Irene Hakansson, Susanne Skyllerstedt, Niels Selling

Other Contributors:

Reinette (Oonsie) Biggs, Juan Carlos Rocha, Håkan Berg

Summary

This case study examines the regime shift caused by the "Nile perch boom" in Lake Victoria, Eastern Africa. The Nile perch, an introduced species, remained a minor component of the lake's cichlid-dominated fauna for more than two decades after its introduction. This regime was maintained by feedbacks between the cichlids and phytoplankton, preventing the lake from oxygen depletion, as well as feedbacks between the cichlids and Nile perch juveniles, controlling the Nile perch population. Human population growth indirectly caused both increased fishing pressure on the cichlids and nutrient input to the lake, eventually leading to the regime shift in the 1980s. The new regime is especially upheld by feedbacks between the Nile perch and cichlids as the latter are the preferred feed of the Nile perch. The ecosystem service impacted the most by the regime shift was fishery, changing from a local and more gender-equalized system to a large-scale international fishing business with local inequalities. For management interventions, the focus is not on reversing the regime shift, but rather on improving social conditions in the lake surroundings. 

Type of regime shift

  • Cichlid dominated state to Nile Perch dominated state

Ecosystem type

  • Freshwater lakes & rivers

Land uses

  • Small-scale subsistence crop cultivation
  • Large-scale commercial crop cultivation
  • Extensive livestock production (natural rangelands)
  • Timber production
  • Fisheries
  • Tourism

Spatial scale of the case study

  • Local/landscape (e.g. lake, catchment, community)

Continent or Ocean

  • Africa

Region

  • Eastern Africa

Countries

  • Tanzania
  • Uganda
  • Kenya

Locate with Google Map

Drivers

Key direct drivers

  • Vegetation conversion and habitat fragmentation
  • Harvest and resource consumption
  • External inputs (eg fertilizers)
  • Adoption of new technology
  • Species introduction or removal
  • Environmental shocks (eg floods)

Impacts

Key Ecosystem Processes

  • Primary production
  • Nutrient cycling

Biodiversity

  • Biodiversity

Provisioning services

  • Freshwater
  • Fisheries

Cultural services

  • Recreation
  • Aesthetic values
  • Knowledge and educational values

Human Well-being

  • Food and nutrition
  • Health (eg toxins, disease)
  • Livelihoods and economic activity
  • Cultural, aesthetic and recreational values
  • Social conflict

Key Attributes

Spatial scale of RS

  • Local/landscape

Time scale of RS

  • Years

Reversibility

  • Unknown

Evidence

  • Models
  • Contemporary observations

Confidence: Existence of RS

  • Well established – Wide agreement in the literature that the RS exists

Confidence: Mechanism underlying RS

  • Well established – Wide agreement on the underlying mechanism

Alternate regimes

Cichlid dominated regime (1950s – 1980s)

The regime was characterized by a lake of high biodiversity dominated by different species of native haplochromine cichlids (Balirwa et al. 2003; UNEP 2010). Cichlids span over many different trophic levels and represent nearly all different functional groups in Lake Victoria (UNEP 2010). In this regime the lake was less eutrophic compared to the current regime and thus less turbid. Nile perch was already introduced to the lake but populations remained low.

In the lake basin there were many local communities living on subsistence farming and small-scale fishing (Swallow 2009). The native fish species provided food for the local communities and the fishing for native cichlids was non-commercial but still population growth in the region put a large pressure on the native fish stocks (Seehausen et al. 1997).

Nile perch-dominated regime (From 1980s)

In this current regime the system has much reduced biodiverse lake with high abundance of only three species, the dominant Nile perch Lates niloticus, Nile tilapia Oreochromis niloticus (Balirwa et al. 2003), and a native cyprinid Rastrineobola argentea (UNEP 2010). The cyprinid is competing for the same resources as some cichlids (Matsuishi et al. 2006) and thus became very abundant once the cichlids disappeared. This low diversity makes the system vulnerable to disturbances (Balirwa et al. 2003; UNEP 2010). Eutrophication is an ever increasing problem resulting in algae blooms, turbidity, and hypoxia (Balirwa et al. 2003), all of which are undesirable conditions for the native species.

The fishing of Nile perch created a global market for fish export. The fishing industries involved many from the local communities and there was an increase in income for those in the Nile perch business. However, the changes brought many social problems emerging from unequal distribution of the increased income (Geheb et al. 2008). 

Drivers and causes of the regime shift

The apparent extinction of several hundreds of cichlid species was caused by Nile perch predation (Goudswaard et al. 2008). However, this event was preceded by drivers that weakened the cichlid population and opened up the field for the Nile perch. One of the main drivers was the increased pressure on the Lake Victoria cichlids by fisheries. At the beginning of the 1980s, cichlids accounted for more than 90 percent of the catch (Balirwa 2007). The other main driver was the increase in nutrient input from the Lake Victoria surroundings, leading to instances of algae blooms and hypoxia. The deoxygenation created an environment which was not suitable for the cichlids, many of which inhabited lower water columns where the oxygen deficiency was most acute (Hecky et al. 1994). The increase in nutrient inputs also caused turbidity which contributed to the reduction of reproductive capacity among cichlids (Seehausen et al. 1997).

The underlying driver of both of these developments is the human population growth around the lake, accelerating fishery activities and off-shore developments such as deforestation and expansion of agriculture which fed the lake with nutrient run-offs (Ibid.). Another cause of the demise of the cichlids was the heavy rainfall events during the 1960s. This external shock destroyed littoral vegetation around the lake which had served as important spawning and nursery grounds for native species. This enabled another species, the Nile tilapia, to conquer some of these areas and outcompete cichlids (Kaufman 1992). At this time the system was resilient enough to avert a shift but these events were precursors to later developments. 

How the regime shift worked

Under the cichlid dominated regime, Lake Victoria was an ecosystem with high species diversity. By eating basically everything in the lake these cichlids performed tight internal recycling (Kaufman 1992) and the pelagic planktivorous and detritivorous cichlids occupied a significant role in protecting the system against the excess production of phytoplankton (Goldschmidt et al. 1993). This allowed allowed resilience against increased nutrient input. The dominance of the cichlids also suppressed other species, including the Nile perch. The cichlids fed upon Nile perch larvae and competed with Nile perch juveniles for space and food (Goudswaard et al. 2008). These dynamics might explain why it took the Nile perch decades to accomplish its virtual takeover of the lake; as long as the cichlids were abundant, the Nile perch reproduction was suppressed (Ibid.).

However, due to the combined threats of Nile perch predation, overfishing, and the increasing nutrient inputs, this changed. First, the overfishing severely reduced the cichlid population in certain areas. Once the cichlid stock was reduced the Nile perch juveniles were able to colonize the areas. From there on, the Nile perch population could grow, invade neighboring areas, reduce the cichlids, and open up new areas for the recruitment of Nile perch juveniles (Ibid.). In this new regime, the Nile perch was the dominator and cichlids then dominated. When the cichlids started to disappear, this situation was opportunistically exploited by other species, including native shrimps. In the absence of the cichlids the shrimp population grew massively and became the most important source of food for the Nile perch (Kaufman 1992, Goldschmidt et al. 1993).

The reduction of cichlids, in combination with the spike in nutrient input, in turn had detrimental effects on the nutrient recycling, resulting in hypoxia. Those cichlids which had inhabited the lower water columns, and had therefore avoided Nile perch, were forced to migrate to shallow waters to escape the hypoxic waters. In these shallow waters they became the target of Nile perch predation (Hecky et al. 1994). 

Impacts on ecosystem services and human well-being

Both before and after the regime shift, Lake Victoria has been providing important provisioning ecosystem services, primarily fisheries. Before the shift, these fisheries were run by small-scale fishermen and operators; women were largely involved in the business (Abila & Jansen 1997), and the fish was for local consumption. However, the Nile perch boom diminished the variety of native fish, and turned this food source into economically more valuable forms of fish meat (Geheb et al. 2008). Foreign investment brought processing plants to the lake's shores (Kaufman 1992), boosted fish export, and eventually turned the artisanal fishery into a large-scale international enterprise. Another provisioning ecosystem service, namely the provision of freshwater suffered from decreased water quality through the cichlids' disappearance (Kaufman 1992).

Cultural ecosystem services were gained in terms of (fishing) tourism but presumably lost in terms of ecosystem/biodiversity knowledge, and aesthetic values. Since the regime shift, the majority of local community members have been carrying out economic activities linked to the Nile Perch fishery. The livelihood for many has improved (Abila & Jansen 1997). However, income from the fishing industry has been unequally distributed (Geheb et al. 2008). Due to social gender inequalities mainly men have been drawing profits from the fisheries boom while women and children have often been victims of malnutrition which is high along the lake's shores (ibid.). Many women have been forced into prostitution which in turn has increased the number of HIV/Aids infections after the Nile perch boom (Appleton 2000). 

Management options

The Nile perch was introduced in Lake Victoria to improve the commercial fishing values (Balirwa et al. 2003). The social effects from this have had huge and diverse impacts on the local communities around the lake resulting in, on one side, a billion dollar export industry, and on the other side, malnutrition, unequally divided income, and increased spread of HIV/Aids (Béné & Merten 2007, Appleton 2000). Nothing was done to prevent the shift from the cichlid dominated regime to the Nile perch dominated regime in the 1980s. Currently there are many different projects that work across the Lake Victoria Basin. The Lake Victoria Basin Commission (LVBC) is an institution of the East African Community which coordinates the policy and management agenda for the region (LVBC 2011). The program works for local community participation, poverty reduction and environmental concerns. Health issues, especially HIV/Aids (LVFO 2011) and human well-being are the most important parts of many different projects working in the lake surroundings. Some projects in the Kenyan part of the Lake Victoria basin mentioned by Swallow 2009 are the TransVic project byWorld Agroforestry Center, the Western Kenya Integrated Ecosystem Management Project and Vi Agroforestry (Swallow 2003 and 2009). These are all focusing on land degradation and agroforestry as land use management methods which both reduce the nutrient input to improve the lake conditions and work for poverty reduction (ibid.). 

A return to a regime with low abundance of Nile perch is not the focus of management and action plans (Schindler et al. 1998, Kitchell 1997) since the economic value of the Nile perch is so important. The ecological focus is rather on restoration of biodiversity, the lake ecosystem services, and the sustainability of the fisheries in the lake. A sustainable fishing of Nile perch can be reached by the control of fishing practices(Seehausen et al. 1997a). A study by Schindler et al. in 1998 show that by using a minimum mesh size of 5-inches the Nile perch cannibalism and the predation of native species can be reduced by 44% at the same time as the catches of Nile perch is only reduced by 10%. The re-emergence of native cichlids is an important step in the lake management to restore biodiversity in the lake system. By continuing the fishing of Nile perch the species is held at a controlled level giving the cichlids an opportunity to return to the system. For this it is also of great importance to improve the lake conditions by reducing the leakage of nutrients into the lake e.g. through investments in sewage treatment and restoration of wetlands in the basin area (Balirwa et al. 2003).

 

 

Key References

  1. Abila, R. and Jansen, E. 1997. From local to global markets: the fish exporting and fishmeal industries of Lake Victoria. IUCN East Africa Programme, Report No. 2. IUCN: Nairobi, Kenya. URL: http://cmsdata.iucn.org/downloads/blue_series_no_2.pdf (29 November 2011).
  2. Appleton, J. 2000 ‘At my age I should be sitting under that tree’: The impact of AIDS on Tanzanian lakeshore communities. Gender and Development 2, pp.19-27.
  3. Balirwa, J. 2007. Ecological, environmental and socioeconomic aspects of the Lake Victoria’s introduced Nile perch fishery in relation to the native fisheries and the species culture potential: Lessons to learn. African Journal of Ecology 45, pp. 120-129.
  4. Balirwa, J. et al. 2003 Biodiversity and fishery sustainability in the Lake Victoria basin: An unexpected marriage? Bioscience 53 (8), pp. 703-716.
  5. Béné, C. and Merten, S. 2007. Women and fish-for-sex: Transactional sex, HIV/AIDS and gender in African fisheries. World Development 36 (5), pp. 875-899.
  6. FAO. 2009. The state of world fisheries and aqua culture (SOFIA) - 2008. FAO: Rome, Italy.
  7. Geheb, K. 1997. The regulators and the regulated: Fisheries management, optionsand dynamics in Kenya's Lake Victoria fishery, Ph.D. thesis, School of African and Asian Studies, University of Sussex.
  8. Geheb, K. et al. 2008. Nile perch and the hungry of Lake Victoria: Gender, status and food in an East African fishery. Food Policy 33 (1), pp. 85-98.
  9. Goldschmidt T., Witte, F., and J. H. Wanink. 1993 Cascading effects of the introduced Nile perch on the detritivorous/phytoplanktivorous species in the sublittoral areas of Lake Victoria. Conservation Biology 7, pp. 686-700.
  10. Goudswaard, P.C. et al. 2011. Distribution of Nile perch Lates niloticus in southern Lake Victoria is determined by depth and dissolved oxygen concentrations. African Journal of Aquatic Science 36 (2), pp. 147–153.
  11. Goudswaard, P.C.,Witte, F., and Katunzi, E.F.B. 2008. The invasion of an introduced predator, Nile perch (Lates niloticus L.) in Lake Victoria (East Africa): Chronology and causes. Environ. Biol. Fish 81, pp. 127-139.
  12. Hecky, R.E. et al. 1994. Deoxygenation of the deep water of Lake Victoria, East Africa. Limnology and Oceanography 39, pp. 1476–1481.
  13. Kansiime F., Saunders, M. J., and Loiselle, S. A. 2007. Functioning and dynamics of wetland vegetation of Lake Victoria: an overview. Wetlands Ecology and Management 15, pp. 443-451.
  14. Kaufman L. 1992. Catastrophic change in species-rich freshwater ecosystems: The lessons of Lake Victoria. BioScience 42, pp. 846-858.
  15. Kitchell, J.F. et al. 1997. The Nile perch in Lake Victoria: Interactions between predation and fisheries. Ecological Application 7(2), pp. 653-664.
  16. Lung’ayia, H., Sitoki, L. and Kenyanya, M. 2001. The nutrient enrichment of Lake Victoria (Kenyan waters). Hydrobiologia 458, pp. 75-82.
  17. LVBC 2011. The Lake Victoria Basin Commission. URL: http://www.lvbcom.org (29 November 2011)
  18. LVFO 2011. The Lake Victoria Fisheries Organization. The Implementation of a Fisheries Management Plan (IFMP) project. URL: http://www.lvfo.org/index.php?option=com_content&view=article&id=68&Itemid=75 (29 November 2011)
  19. Maitima, J.M. et al. 2010 Land use changes, impacts and options for sustaining productivity and livelihoods in the basin of Lake Victoria. Journal of Sustainable Development 12 (3), pp. 189-90.
  20. Matsuishi, T. et al. 2006. Are the exploitation pressures on the Nile perch fisheries resources of Lake Victoria a cause for concern? Fisheries Management and Ecology 13, pp. 53-71.
  21. Reynold, J. E. and Gréboval, D. F. 1989 Socio-economic effects of the evolution of Nile perch fisheries in Lake Victoria: a review. FAO: Rome, Italy.
  22. Schindler, D.E., Kitchell, J.F., and Ogutu-Ohwayo, R. 1998. Ecological consequences of alternative gill net fisheries for Nile perch in Lake Victoria. Conservation Biology 12, pp. 56-64.
  23. Seehausen, O. et al. 1997. Patterns of the remnant cichlid fauna in Southern Lake Victoria. Conservation Biology 11 (4), pp. 890-904
  24. Seehausen, O., van Alphen, J.M., and Witte, F. 1997. Cichlid fish diversity threatened by eutrophication that curbs sexual selection. Science 277, pp. 1808-1811.
  25. Swallow, B. 2009. Tradeoffs, synergies and traps among ecosystem services in the Lake Victoria basin of East Africa. Environmental science & policy 12, pp. 504-519.
  26. UNEP 2010. Blue harvest: Inland fisheries as an ecosystem service. World Fish Center: Penang, Malaysia.
  27. Verschuren, D. et al. 2002. History and timing of human impact on Lake Victoria, East Africa. Proc. R. Soc. Lond. Ser. B 269, pp. 289–294.

Citation

Irene Hakansson, Susanne Skyllerstedt, Niels Selling, Reinette (Oonsie) Biggs, Juan Carlos Rocha, Håkan Berg. Lake Victoria. In: Regime Shifts Database, www.regimeshifts.org. Last revised 2012-03-20 14:17:24 GMT.
Monday, 19 March 2012 12:04

North Pacific Ocean

Written by Johanna

North Pacific Ocean

Main Contributors:

Johanna Yletyinen

Other Contributors:

Thorsten Blenckner, Reinette (Oonsie) Biggs

Summary

A climatic regime shift took place in the North Pacific Ocean during the winter 1976-77. It caused significant impacts on the physical and biological conditions leading to severe distribution and abundance changes of plankton and fish species. Physical changes include intensification of the wintertime Aleutian Low pressure system, change in Pacific-North America (PNA) teleconnection pattern, and regional cooling or warming. The 1977 climate shift is associated with an abrupt transition from a negative to positive phase of the Pacific Decadal Oscillation (PDO). In 1989, a new regime shift occurred characterized by declining fish stocks, but the changes were not as remarkable or pervasive as in the 1976-77, and the changes caused not a return of the system back to the pre-1977 conditions. The 1976-77 and 1989 North Pacific Ocean climatic regime shifts were caused by natural shifts in ocean climate. Studies have shown that regime shifts have occurred in the North Pacific for centuries, although their durations seem to have diminished from 50-100 years to even 10 years. 

Type of regime shift

  • Climatic Regime Shift

Ecosystem type

  • Marine & coastal

Land uses

  • Fisheries

Spatial scale of the case study

  • Sub-continental/regional (e.g. southern Africa, Amazon basin)

Continent or Ocean

  • Pacific Ocean

Region

  • North Pacific Ocean

Countries

  • Not relevant

Locate with Google Map

Drivers

Key direct drivers

  • Vegetation conversion and habitat fragmentation
  • Harvest and resource consumption
  • External inputs (eg fertilizers)
  • Adoption of new technology
  • Species introduction or removal
  • Environmental shocks (eg floods)

Impacts

Key Ecosystem Processes

  • Primary production
  • Nutrient cycling

Biodiversity

  • Biodiversity

Provisioning services

  • Freshwater
  • Fisheries

Cultural services

  • Recreation
  • Aesthetic values
  • Knowledge and educational values

Human Well-being

  • Food and nutrition
  • Health (eg toxins, disease)
  • Livelihoods and economic activity
  • Cultural, aesthetic and recreational values
  • Social conflict

Key Attributes

Spatial scale of RS

  • Local/landscape

Time scale of RS

  • Years

Reversibility

  • Unknown

Evidence

  • Models
  • Contemporary observations

Confidence: Existence of RS

  • Well established – Wide agreement in the literature that the RS exists

Confidence: Mechanism underlying RS

  • Well established – Wide agreement on the underlying mechanism

Alternate regimes

Cichlid dominated regime (1950s – 1980s)

The regime was characterized by a lake of high biodiversity dominated by different species of native haplochromine cichlids (Balirwa et al. 2003; UNEP 2010). Cichlids span over many different trophic levels and represent nearly all different functional groups in Lake Victoria (UNEP 2010). In this regime the lake was less eutrophic compared to the current regime and thus less turbid. Nile perch was already introduced to the lake but populations remained low.

In the lake basin there were many local communities living on subsistence farming and small-scale fishing (Swallow 2009). The native fish species provided food for the local communities and the fishing for native cichlids was non-commercial but still population growth in the region put a large pressure on the native fish stocks (Seehausen et al. 1997).

Nile perch-dominated regime (From 1980s)

In this current regime the system has much reduced biodiverse lake with high abundance of only three species, the dominant Nile perch Lates niloticus, Nile tilapia Oreochromis niloticus (Balirwa et al. 2003), and a native cyprinid Rastrineobola argentea (UNEP 2010). The cyprinid is competing for the same resources as some cichlids (Matsuishi et al. 2006) and thus became very abundant once the cichlids disappeared. This low diversity makes the system vulnerable to disturbances (Balirwa et al. 2003; UNEP 2010). Eutrophication is an ever increasing problem resulting in algae blooms, turbidity, and hypoxia (Balirwa et al. 2003), all of which are undesirable conditions for the native species.

The fishing of Nile perch created a global market for fish export. The fishing industries involved many from the local communities and there was an increase in income for those in the Nile perch business. However, the changes brought many social problems emerging from unequal distribution of the increased income (Geheb et al. 2008). 

Drivers and causes of the regime shift

The apparent extinction of several hundreds of cichlid species was caused by Nile perch predation (Goudswaard et al. 2008). However, this event was preceded by drivers that weakened the cichlid population and opened up the field for the Nile perch. One of the main drivers was the increased pressure on the Lake Victoria cichlids by fisheries. At the beginning of the 1980s, cichlids accounted for more than 90 percent of the catch (Balirwa 2007). The other main driver was the increase in nutrient input from the Lake Victoria surroundings, leading to instances of algae blooms and hypoxia. The deoxygenation created an environment which was not suitable for the cichlids, many of which inhabited lower water columns where the oxygen deficiency was most acute (Hecky et al. 1994). The increase in nutrient inputs also caused turbidity which contributed to the reduction of reproductive capacity among cichlids (Seehausen et al. 1997).

The underlying driver of both of these developments is the human population growth around the lake, accelerating fishery activities and off-shore developments such as deforestation and expansion of agriculture which fed the lake with nutrient run-offs (Ibid.). Another cause of the demise of the cichlids was the heavy rainfall events during the 1960s. This external shock destroyed littoral vegetation around the lake which had served as important spawning and nursery grounds for native species. This enabled another species, the Nile tilapia, to conquer some of these areas and outcompete cichlids (Kaufman 1992). At this time the system was resilient enough to avert a shift but these events were precursors to later developments. 

How the regime shift worked

Under the cichlid dominated regime, Lake Victoria was an ecosystem with high species diversity. By eating basically everything in the lake these cichlids performed tight internal recycling (Kaufman 1992) and the pelagic planktivorous and detritivorous cichlids occupied a significant role in protecting the system against the excess production of phytoplankton (Goldschmidt et al. 1993). This allowed allowed resilience against increased nutrient input. The dominance of the cichlids also suppressed other species, including the Nile perch. The cichlids fed upon Nile perch larvae and competed with Nile perch juveniles for space and food (Goudswaard et al. 2008). These dynamics might explain why it took the Nile perch decades to accomplish its virtual takeover of the lake; as long as the cichlids were abundant, the Nile perch reproduction was suppressed (Ibid.).

However, due to the combined threats of Nile perch predation, overfishing, and the increasing nutrient inputs, this changed. First, the overfishing severely reduced the cichlid population in certain areas. Once the cichlid stock was reduced the Nile perch juveniles were able to colonize the areas. From there on, the Nile perch population could grow, invade neighboring areas, reduce the cichlids, and open up new areas for the recruitment of Nile perch juveniles (Ibid.). In this new regime, the Nile perch was the dominator and cichlids then dominated. When the cichlids started to disappear, this situation was opportunistically exploited by other species, including native shrimps. In the absence of the cichlids the shrimp population grew massively and became the most important source of food for the Nile perch (Kaufman 1992, Goldschmidt et al. 1993).

The reduction of cichlids, in combination with the spike in nutrient input, in turn had detrimental effects on the nutrient recycling, resulting in hypoxia. Those cichlids which had inhabited the lower water columns, and had therefore avoided Nile perch, were forced to migrate to shallow waters to escape the hypoxic waters. In these shallow waters they became the target of Nile perch predation (Hecky et al. 1994). 

Impacts on ecosystem services and human well-being

Both before and after the regime shift, Lake Victoria has been providing important provisioning ecosystem services, primarily fisheries. Before the shift, these fisheries were run by small-scale fishermen and operators; women were largely involved in the business (Abila & Jansen 1997), and the fish was for local consumption. However, the Nile perch boom diminished the variety of native fish, and turned this food source into economically more valuable forms of fish meat (Geheb et al. 2008). Foreign investment brought processing plants to the lake's shores (Kaufman 1992), boosted fish export, and eventually turned the artisanal fishery into a large-scale international enterprise. Another provisioning ecosystem service, namely the provision of freshwater suffered from decreased water quality through the cichlids' disappearance (Kaufman 1992).

Cultural ecosystem services were gained in terms of (fishing) tourism but presumably lost in terms of ecosystem/biodiversity knowledge, and aesthetic values. Since the regime shift, the majority of local community members have been carrying out economic activities linked to the Nile Perch fishery. The livelihood for many has improved (Abila & Jansen 1997). However, income from the fishing industry has been unequally distributed (Geheb et al. 2008). Due to social gender inequalities mainly men have been drawing profits from the fisheries boom while women and children have often been victims of malnutrition which is high along the lake's shores (ibid.). Many women have been forced into prostitution which in turn has increased the number of HIV/Aids infections after the Nile perch boom (Appleton 2000). 

Management options

The Nile perch was introduced in Lake Victoria to improve the commercial fishing values (Balirwa et al. 2003). The social effects from this have had huge and diverse impacts on the local communities around the lake resulting in, on one side, a billion dollar export industry, and on the other side, malnutrition, unequally divided income, and increased spread of HIV/Aids (Béné & Merten 2007, Appleton 2000). Nothing was done to prevent the shift from the cichlid dominated regime to the Nile perch dominated regime in the 1980s. Currently there are many different projects that work across the Lake Victoria Basin. The Lake Victoria Basin Commission (LVBC) is an institution of the East African Community which coordinates the policy and management agenda for the region (LVBC 2011). The program works for local community participation, poverty reduction and environmental concerns. Health issues, especially HIV/Aids (LVFO 2011) and human well-being are the most important parts of many different projects working in the lake surroundings. Some projects in the Kenyan part of the Lake Victoria basin mentioned by Swallow 2009 are the TransVic project byWorld Agroforestry Center, the Western Kenya Integrated Ecosystem Management Project and Vi Agroforestry (Swallow 2003 and 2009). These are all focusing on land degradation and agroforestry as land use management methods which both reduce the nutrient input to improve the lake conditions and work for poverty reduction (ibid.). 

A return to a regime with low abundance of Nile perch is not the focus of management and action plans (Schindler et al. 1998, Kitchell 1997) since the economic value of the Nile perch is so important. The ecological focus is rather on restoration of biodiversity, the lake ecosystem services, and the sustainability of the fisheries in the lake. A sustainable fishing of Nile perch can be reached by the control of fishing practices(Seehausen et al. 1997a). A study by Schindler et al. in 1998 show that by using a minimum mesh size of 5-inches the Nile perch cannibalism and the predation of native species can be reduced by 44% at the same time as the catches of Nile perch is only reduced by 10%. The re-emergence of native cichlids is an important step in the lake management to restore biodiversity in the lake system. By continuing the fishing of Nile perch the species is held at a controlled level giving the cichlids an opportunity to return to the system. For this it is also of great importance to improve the lake conditions by reducing the leakage of nutrients into the lake e.g. through investments in sewage treatment and restoration of wetlands in the basin area (Balirwa et al. 2003).

 

 

Alternate regimes

Cichlid dominated regime (1950s – 1980s)

The regime was characterized by a lake of high biodiversity dominated by different species of native haplochromine cichlids (Balirwa et al. 2003; UNEP 2010). Cichlids span over many different trophic levels and represent nearly all different functional groups in Lake Victoria (UNEP 2010). In this regime the lake was less eutrophic compared to the current regime and thus less turbid. Nile perch was already introduced to the lake but populations remained low.

In the lake basin there were many local communities living on subsistence farming and small-scale fishing (Swallow 2009). The native fish species provided food for the local communities and the fishing for native cichlids was non-commercial but still population growth in the region put a large pressure on the native fish stocks (Seehausen et al. 1997).

Nile perch-dominated regime (From 1980s)

In this current regime the system has much reduced biodiverse lake with high abundance of only three species, the dominant Nile perch Lates niloticus, Nile tilapia Oreochromis niloticus (Balirwa et al. 2003), and a native cyprinid Rastrineobola argentea (UNEP 2010). The cyprinid is competing for the same resources as some cichlids (Matsuishi et al. 2006) and thus became very abundant once the cichlids disappeared. This low diversity makes the system vulnerable to disturbances (Balirwa et al. 2003; UNEP 2010). Eutrophication is an ever increasing problem resulting in algae blooms, turbidity, and hypoxia (Balirwa et al. 2003), all of which are undesirable conditions for the native species.

The fishing of Nile perch created a global market for fish export. The fishing industries involved many from the local communities and there was an increase in income for those in the Nile perch business. However, the changes brought many social problems emerging from unequal distribution of the increased income (Geheb et al. 2008). 

Drivers and causes of the regime shift

The apparent extinction of several hundreds of cichlid species was caused by Nile perch predation (Goudswaard et al. 2008). However, this event was preceded by drivers that weakened the cichlid population and opened up the field for the Nile perch. One of the main drivers was the increased pressure on the Lake Victoria cichlids by fisheries. At the beginning of the 1980s, cichlids accounted for more than 90 percent of the catch (Balirwa 2007). The other main driver was the increase in nutrient input from the Lake Victoria surroundings, leading to instances of algae blooms and hypoxia. The deoxygenation created an environment which was not suitable for the cichlids, many of which inhabited lower water columns where the oxygen deficiency was most acute (Hecky et al. 1994). The increase in nutrient inputs also caused turbidity which contributed to the reduction of reproductive capacity among cichlids (Seehausen et al. 1997).

The underlying driver of both of these developments is the human population growth around the lake, accelerating fishery activities and off-shore developments such as deforestation and expansion of agriculture which fed the lake with nutrient run-offs (Ibid.). Another cause of the demise of the cichlids was the heavy rainfall events during the 1960s. This external shock destroyed littoral vegetation around the lake which had served as important spawning and nursery grounds for native species. This enabled another species, the Nile tilapia, to conquer some of these areas and outcompete cichlids (Kaufman 1992). At this time the system was resilient enough to avert a shift but these events were precursors to later developments. 

How the regime shift worked

Under the cichlid dominated regime, Lake Victoria was an ecosystem with high species diversity. By eating basically everything in the lake these cichlids performed tight internal recycling (Kaufman 1992) and the pelagic planktivorous and detritivorous cichlids occupied a significant role in protecting the system against the excess production of phytoplankton (Goldschmidt et al. 1993). This allowed allowed resilience against increased nutrient input. The dominance of the cichlids also suppressed other species, including the Nile perch. The cichlids fed upon Nile perch larvae and competed with Nile perch juveniles for space and food (Goudswaard et al. 2008). These dynamics might explain why it took the Nile perch decades to accomplish its virtual takeover of the lake; as long as the cichlids were abundant, the Nile perch reproduction was suppressed (Ibid.).

However, due to the combined threats of Nile perch predation, overfishing, and the increasing nutrient inputs, this changed. First, the overfishing severely reduced the cichlid population in certain areas. Once the cichlid stock was reduced the Nile perch juveniles were able to colonize the areas. From there on, the Nile perch population could grow, invade neighboring areas, reduce the cichlids, and open up new areas for the recruitment of Nile perch juveniles (Ibid.). In this new regime, the Nile perch was the dominator and cichlids then dominated. When the cichlids started to disappear, this situation was opportunistically exploited by other species, including native shrimps. In the absence of the cichlids the shrimp population grew massively and became the most important source of food for the Nile perch (Kaufman 1992, Goldschmidt et al. 1993).

The reduction of cichlids, in combination with the spike in nutrient input, in turn had detrimental effects on the nutrient recycling, resulting in hypoxia. Those cichlids which had inhabited the lower water columns, and had therefore avoided Nile perch, were forced to migrate to shallow waters to escape the hypoxic waters. In these shallow waters they became the target of Nile perch predation (Hecky et al. 1994). 

Impacts on ecosystem services and human well-being

Both before and after the regime shift, Lake Victoria has been providing important provisioning ecosystem services, primarily fisheries. Before the shift, these fisheries were run by small-scale fishermen and operators; women were largely involved in the business (Abila & Jansen 1997), and the fish was for local consumption. However, the Nile perch boom diminished the variety of native fish, and turned this food source into economically more valuable forms of fish meat (Geheb et al. 2008). Foreign investment brought processing plants to the lake's shores (Kaufman 1992), boosted fish export, and eventually turned the artisanal fishery into a large-scale international enterprise. Another provisioning ecosystem service, namely the provision of freshwater suffered from decreased water quality through the cichlids' disappearance (Kaufman 1992).

Cultural ecosystem services were gained in terms of (fishing) tourism but presumably lost in terms of ecosystem/biodiversity knowledge, and aesthetic values. Since the regime shift, the majority of local community members have been carrying out economic activities linked to the Nile Perch fishery. The livelihood for many has improved (Abila & Jansen 1997). However, income from the fishing industry has been unequally distributed (Geheb et al. 2008). Due to social gender inequalities mainly men have been drawing profits from the fisheries boom while women and children have often been victims of malnutrition which is high along the lake's shores (ibid.). Many women have been forced into prostitution which in turn has increased the number of HIV/Aids infections after the Nile perch boom (Appleton 2000). 

Management options

The Nile perch was introduced in Lake Victoria to improve the commercial fishing values (Balirwa et al. 2003). The social effects from this have had huge and diverse impacts on the local communities around the lake resulting in, on one side, a billion dollar export industry, and on the other side, malnutrition, unequally divided income, and increased spread of HIV/Aids (Béné & Merten 2007, Appleton 2000). Nothing was done to prevent the shift from the cichlid dominated regime to the Nile perch dominated regime in the 1980s. Currently there are many different projects that work across the Lake Victoria Basin. The Lake Victoria Basin Commission (LVBC) is an institution of the East African Community which coordinates the policy and management agenda for the region (LVBC 2011). The program works for local community participation, poverty reduction and environmental concerns. Health issues, especially HIV/Aids (LVFO 2011) and human well-being are the most important parts of many different projects working in the lake surroundings. Some projects in the Kenyan part of the Lake Victoria basin mentioned by Swallow 2009 are the TransVic project byWorld Agroforestry Center, the Western Kenya Integrated Ecosystem Management Project and Vi Agroforestry (Swallow 2003 and 2009). These are all focusing on land degradation and agroforestry as land use management methods which both reduce the nutrient input to improve the lake conditions and work for poverty reduction (ibid.). 

A return to a regime with low abundance of Nile perch is not the focus of management and action plans (Schindler et al. 1998, Kitchell 1997) since the economic value of the Nile perch is so important. The ecological focus is rather on restoration of biodiversity, the lake ecosystem services, and the sustainability of the fisheries in the lake. A sustainable fishing of Nile perch can be reached by the control of fishing practices(Seehausen et al. 1997a). A study by Schindler et al. in 1998 show that by using a minimum mesh size of 5-inches the Nile perch cannibalism and the predation of native species can be reduced by 44% at the same time as the catches of Nile perch is only reduced by 10%. The re-emergence of native cichlids is an important step in the lake management to restore biodiversity in the lake system. By continuing the fishing of Nile perch the species is held at a controlled level giving the cichlids an opportunity to return to the system. For this it is also of great importance to improve the lake conditions by reducing the leakage of nutrients into the lake e.g. through investments in sewage treatment and restoration of wetlands in the basin area (Balirwa et al. 2003).

 

 

Key References

  1. Alexander M, Capotondi A, Miller A, Chai F, Brodeur R, Deser C. 2008. Decadal variability in the northeast Pacific in a physical-ecosystem model: Role of mixed layer depth and trophic interactions. Journal of Geophysical Research 113, 1-13.
  2. Alheit J, Bakun A. 2010. Population synchronies within and between ocean basins: Apparent teleconnections and implications as to physical-biological linkage mechanisms. Journal of Marine Systes 79, 267-285.
  3. Anderson PJ, Piatt JF. 1999. Community reorganization in the Gulf of Alaska following ocean climate regime shift. Marine Ecology Progress Series 189, 117-123.
  4. Badjeck M-C, Allison EH, Halls AS, Dulvy NK. 2010. Impacts of climate variability and change on fishery-based livelihoods. Marine Policy 34, 357-383.
  5. Benson AJ, Trites AW. 2002. Ecological effects of regime shifts in the Bering Sea and eastern North Pacific Ocean. Fish and Fisheries 3, 95-113.
  6. Benson AJ, Trites AW. 2002. Ecological effects of regime shifts in the Bering Sea and eastern North Pacific Ocean. Fish and Fisheries 3, 95-113.
  7. Chavez FP, Ryan J, Lluch-Cota SE, Niquen MC. 2003. From anchovies to sardines and back: multidecaldal change in the Pacific Ocean. Science 299, 217-221.
  8. Chiba S, Aita MN, Tadokoro K, Saino T, Sugisaki H, Nakata K. From climate regime shifts to lower-trophic level phenology: Synthesis of recent progess in retrospective studies of the western North Pacific. Progress in Oceanography 77, 112-126.
  9. Drinkwater KF, Beaugrand G, Kaeriyama M, Kim S, Ottersen G, Perry RI, Pörtner HO, Polovina JJ, Takasuka A. 2010. On the processes linking climate to ecosystem changes. Journal of Marine Systems 79, 374-488.
  10. Hare SR, Mantua NJ. 2000. Empirical evidence for North Pacific regime shifts in 1977 and 1989. Progress in Oceanography 47, 103-145.
  11. Hartmann B, Wendler G. 2005. The significance of the 1976 Pacific climate shift in the climatology of Alaska. Journal of Climate 18, 4824-4839.
  12. Jin FF. 1997. A theory of interdecadal climate variability of the North Pacific ocean-atmosphere system. Journal of Climate 10, 1821-1835.
  13. McBeath J. 2004. Management of the commons for biodiversity: lessons from the North Pacific. Marine Policy 28, 523-539.
  14. McGowan JA, Bograd SJ, Lynn RJ, Miller AJ. 2003. The biological response to the 1977 regime shift in the California Current. Deep Sea Research II 50, 2567-2582.
  15. McGowan JA, Cayan DR, Dorman LM. 1998. Climate-ocean variability and ecosystem response in the Northeast Pacific. Science 281, 210-217.
  16. Megrey BA, Rose KA, Shin-ichi I, Hay DE, Werner FE, Yamanaka Y, Aita MN. 2007. North Pacific basin-scale differences in lower and higher trophic level marine ecosystem responses to claimte impacts using a nutrient-phytoplankton-zooplankton model coupled to a fish bioenergetics model. Ecological Modelling 202, 196-210.
  17. Miller AJ, Schneider N. 2000. Interdecadal climate regime dynamics in the North Pacific Ocean: theories, observations and ecosystem impacts. Progress in Oceanography 47, 355-379.
  18. Overland J, Rodionov S, Minobe S, Bond N. 2008. North Pacific regime shifts: Definitions, issues and recent transitions. Progress in Oceanography 77, 92-102.
  19. Wooster WS, Zhang CI. 2004. Regime shifts in the North Pacific: early indications of the 1976-1977 event. Progress in Oceanography 60, 183-200
  20. Wu L, Lee DE, Liu Z. 2005. The 1976/77 North Pacific climate regime shift: the role of subtropical ocean adjustment and coupled ocean-atmosphere feedbacks. Journal of Climate 18, 5125-5140.
  21. Yatsu A, Aydin KY, King JR, McFarlane GA, Chiba S, Tadokoro K, Kaeriyama M, Watanabe Y. 2008. Elucidating dynamic responses of North Pacific fish populations to climatic forcing: Influence of life-history strategy. Progress in Oceanography 77, 252-268.
  22. Yoo S, Batchelder HP, Peterson WT, Sydeman WJ. 2008. Seasonal, interannual and event scale variation in North Pacific ecosystems. Progress in Oceanography 77, 155-181.
  23. Zhang CI, Lee JB, Kim S, Oh J-H. 2000. Climatic regime shifts and their impacts on marine fisheries resources in Korean waters. Progress in Oceanography 41, 171-190.

Citation

Johanna Yletyinen, Thorsten Blenckner, Reinette (Oonsie) Biggs. North Pacific Ocean. In: Regime Shifts Database, www.regimeshifts.org. Last revised 2012-11-20 12:10:02 GMT.
Thursday, 15 March 2012 17:02

Yellow River delta, China

Written by Reinette (Oonsie) Biggs

Yellow River delta, China

Main Contributors:

Henning Nolzen

Other Contributors:

Reinette (Oonsie) Biggs, Garry Peterson

Summary

In the history of the formation of the Yellow River delta complex, several shifts in the lower river channel and in the tributary channels have occurred over the last 6000 years. Shifts in the tributary channels caused by silting up in the river mouth because of deposition of sediment which heightened the channel floor. Headward deposition as well as the formation of superlobes was also a driver for channel shifts in the tributaries. Superlobes can either be a result of lower channel shifts through movement of the river mouth or a result of formation of several delta lobes which in turn are caused tributary channel shifts (reinforcing feedback). The shifts in the lower river channel and in the distributaries led to complicated imbrication. Moreover, changes in the coastlines, and sea water depth took place because of these river channel shifts. Lower river channel shifts were brought under artificial control by dykes, or under natural conditions by formation of large crevasses due to deposition of sediment. A large crevasse was for example formed in 1855 and in 1128 a dyke was destroyed to check the advance of the Jin army.

Type of regime shift

Ecosystem type

  • Freshwater lakes & rivers

Land uses

  • Urban
  • Small-scale subsistence crop cultivation
  • Fisheries

Spatial scale of the case study

  • Local/landscape (e.g. lake, catchment, community)

Continent or Ocean

  • Asia

Region

  • Shandong Province, China

Countries

  • China, People's Republic of

Locate with Google Map

Alternate regimes

Cichlid dominated regime (1950s – 1980s)

The regime was characterized by a lake of high biodiversity dominated by different species of native haplochromine cichlids (Balirwa et al. 2003; UNEP 2010). Cichlids span over many different trophic levels and represent nearly all different functional groups in Lake Victoria (UNEP 2010). In this regime the lake was less eutrophic compared to the current regime and thus less turbid. Nile perch was already introduced to the lake but populations remained low.

In the lake basin there were many local communities living on subsistence farming and small-scale fishing (Swallow 2009). The native fish species provided food for the local communities and the fishing for native cichlids was non-commercial but still population growth in the region put a large pressure on the native fish stocks (Seehausen et al. 1997).

Nile perch-dominated regime (From 1980s)

In this current regime the system has much reduced biodiverse lake with high abundance of only three species, the dominant Nile perch Lates niloticus, Nile tilapia Oreochromis niloticus (Balirwa et al. 2003), and a native cyprinid Rastrineobola argentea (UNEP 2010). The cyprinid is competing for the same resources as some cichlids (Matsuishi et al. 2006) and thus became very abundant once the cichlids disappeared. This low diversity makes the system vulnerable to disturbances (Balirwa et al. 2003; UNEP 2010). Eutrophication is an ever increasing problem resulting in algae blooms, turbidity, and hypoxia (Balirwa et al. 2003), all of which are undesirable conditions for the native species.

The fishing of Nile perch created a global market for fish export. The fishing industries involved many from the local communities and there was an increase in income for those in the Nile perch business. However, the changes brought many social problems emerging from unequal distribution of the increased income (Geheb et al. 2008). 

Drivers and causes of the regime shift

The apparent extinction of several hundreds of cichlid species was caused by Nile perch predation (Goudswaard et al. 2008). However, this event was preceded by drivers that weakened the cichlid population and opened up the field for the Nile perch. One of the main drivers was the increased pressure on the Lake Victoria cichlids by fisheries. At the beginning of the 1980s, cichlids accounted for more than 90 percent of the catch (Balirwa 2007). The other main driver was the increase in nutrient input from the Lake Victoria surroundings, leading to instances of algae blooms and hypoxia. The deoxygenation created an environment which was not suitable for the cichlids, many of which inhabited lower water columns where the oxygen deficiency was most acute (Hecky et al. 1994). The increase in nutrient inputs also caused turbidity which contributed to the reduction of reproductive capacity among cichlids (Seehausen et al. 1997).

The underlying driver of both of these developments is the human population growth around the lake, accelerating fishery activities and off-shore developments such as deforestation and expansion of agriculture which fed the lake with nutrient run-offs (Ibid.). Another cause of the demise of the cichlids was the heavy rainfall events during the 1960s. This external shock destroyed littoral vegetation around the lake which had served as important spawning and nursery grounds for native species. This enabled another species, the Nile tilapia, to conquer some of these areas and outcompete cichlids (Kaufman 1992). At this time the system was resilient enough to avert a shift but these events were precursors to later developments. 

How the regime shift worked

Under the cichlid dominated regime, Lake Victoria was an ecosystem with high species diversity. By eating basically everything in the lake these cichlids performed tight internal recycling (Kaufman 1992) and the pelagic planktivorous and detritivorous cichlids occupied a significant role in protecting the system against the excess production of phytoplankton (Goldschmidt et al. 1993). This allowed allowed resilience against increased nutrient input. The dominance of the cichlids also suppressed other species, including the Nile perch. The cichlids fed upon Nile perch larvae and competed with Nile perch juveniles for space and food (Goudswaard et al. 2008). These dynamics might explain why it took the Nile perch decades to accomplish its virtual takeover of the lake; as long as the cichlids were abundant, the Nile perch reproduction was suppressed (Ibid.).

However, due to the combined threats of Nile perch predation, overfishing, and the increasing nutrient inputs, this changed. First, the overfishing severely reduced the cichlid population in certain areas. Once the cichlid stock was reduced the Nile perch juveniles were able to colonize the areas. From there on, the Nile perch population could grow, invade neighboring areas, reduce the cichlids, and open up new areas for the recruitment of Nile perch juveniles (Ibid.). In this new regime, the Nile perch was the dominator and cichlids then dominated. When the cichlids started to disappear, this situation was opportunistically exploited by other species, including native shrimps. In the absence of the cichlids the shrimp population grew massively and became the most important source of food for the Nile perch (Kaufman 1992, Goldschmidt et al. 1993).

The reduction of cichlids, in combination with the spike in nutrient input, in turn had detrimental effects on the nutrient recycling, resulting in hypoxia. Those cichlids which had inhabited the lower water columns, and had therefore avoided Nile perch, were forced to migrate to shallow waters to escape the hypoxic waters. In these shallow waters they became the target of Nile perch predation (Hecky et al. 1994). 

Impacts on ecosystem services and human well-being

Both before and after the regime shift, Lake Victoria has been providing important provisioning ecosystem services, primarily fisheries. Before the shift, these fisheries were run by small-scale fishermen and operators; women were largely involved in the business (Abila & Jansen 1997), and the fish was for local consumption. However, the Nile perch boom diminished the variety of native fish, and turned this food source into economically more valuable forms of fish meat (Geheb et al. 2008). Foreign investment brought processing plants to the lake's shores (Kaufman 1992), boosted fish export, and eventually turned the artisanal fishery into a large-scale international enterprise. Another provisioning ecosystem service, namely the provision of freshwater suffered from decreased water quality through the cichlids' disappearance (Kaufman 1992).

Cultural ecosystem services were gained in terms of (fishing) tourism but presumably lost in terms of ecosystem/biodiversity knowledge, and aesthetic values. Since the regime shift, the majority of local community members have been carrying out economic activities linked to the Nile Perch fishery. The livelihood for many has improved (Abila & Jansen 1997). However, income from the fishing industry has been unequally distributed (Geheb et al. 2008). Due to social gender inequalities mainly men have been drawing profits from the fisheries boom while women and children have often been victims of malnutrition which is high along the lake's shores (ibid.). Many women have been forced into prostitution which in turn has increased the number of HIV/Aids infections after the Nile perch boom (Appleton 2000). 

Management options

The Nile perch was introduced in Lake Victoria to improve the commercial fishing values (Balirwa et al. 2003). The social effects from this have had huge and diverse impacts on the local communities around the lake resulting in, on one side, a billion dollar export industry, and on the other side, malnutrition, unequally divided income, and increased spread of HIV/Aids (Béné & Merten 2007, Appleton 2000). Nothing was done to prevent the shift from the cichlid dominated regime to the Nile perch dominated regime in the 1980s. Currently there are many different projects that work across the Lake Victoria Basin. The Lake Victoria Basin Commission (LVBC) is an institution of the East African Community which coordinates the policy and management agenda for the region (LVBC 2011). The program works for local community participation, poverty reduction and environmental concerns. Health issues, especially HIV/Aids (LVFO 2011) and human well-being are the most important parts of many different projects working in the lake surroundings. Some projects in the Kenyan part of the Lake Victoria basin mentioned by Swallow 2009 are the TransVic project byWorld Agroforestry Center, the Western Kenya Integrated Ecosystem Management Project and Vi Agroforestry (Swallow 2003 and 2009). These are all focusing on land degradation and agroforestry as land use management methods which both reduce the nutrient input to improve the lake conditions and work for poverty reduction (ibid.). 

A return to a regime with low abundance of Nile perch is not the focus of management and action plans (Schindler et al. 1998, Kitchell 1997) since the economic value of the Nile perch is so important. The ecological focus is rather on restoration of biodiversity, the lake ecosystem services, and the sustainability of the fisheries in the lake. A sustainable fishing of Nile perch can be reached by the control of fishing practices(Seehausen et al. 1997a). A study by Schindler et al. in 1998 show that by using a minimum mesh size of 5-inches the Nile perch cannibalism and the predation of native species can be reduced by 44% at the same time as the catches of Nile perch is only reduced by 10%. The re-emergence of native cichlids is an important step in the lake management to restore biodiversity in the lake system. By continuing the fishing of Nile perch the species is held at a controlled level giving the cichlids an opportunity to return to the system. For this it is also of great importance to improve the lake conditions by reducing the leakage of nutrients into the lake e.g. through investments in sewage treatment and restoration of wetlands in the basin area (Balirwa et al. 2003).

 

 

Alternate regimes

Cichlid dominated regime (1950s – 1980s)

The regime was characterized by a lake of high biodiversity dominated by different species of native haplochromine cichlids (Balirwa et al. 2003; UNEP 2010). Cichlids span over many different trophic levels and represent nearly all different functional groups in Lake Victoria (UNEP 2010). In this regime the lake was less eutrophic compared to the current regime and thus less turbid. Nile perch was already introduced to the lake but populations remained low.

In the lake basin there were many local communities living on subsistence farming and small-scale fishing (Swallow 2009). The native fish species provided food for the local communities and the fishing for native cichlids was non-commercial but still population growth in the region put a large pressure on the native fish stocks (Seehausen et al. 1997).

Nile perch-dominated regime (From 1980s)

In this current regime the system has much reduced biodiverse lake with high abundance of only three species, the dominant Nile perch Lates niloticus, Nile tilapia Oreochromis niloticus (Balirwa et al. 2003), and a native cyprinid Rastrineobola argentea (UNEP 2010). The cyprinid is competing for the same resources as some cichlids (Matsuishi et al. 2006) and thus became very abundant once the cichlids disappeared. This low diversity makes the system vulnerable to disturbances (Balirwa et al. 2003; UNEP 2010). Eutrophication is an ever increasing problem resulting in algae blooms, turbidity, and hypoxia (Balirwa et al. 2003), all of which are undesirable conditions for the native species.

The fishing of Nile perch created a global market for fish export. The fishing industries involved many from the local communities and there was an increase in income for those in the Nile perch business. However, the changes brought many social problems emerging from unequal distribution of the increased income (Geheb et al. 2008). 

Drivers and causes of the regime shift

The apparent extinction of several hundreds of cichlid species was caused by Nile perch predation (Goudswaard et al. 2008). However, this event was preceded by drivers that weakened the cichlid population and opened up the field for the Nile perch. One of the main drivers was the increased pressure on the Lake Victoria cichlids by fisheries. At the beginning of the 1980s, cichlids accounted for more than 90 percent of the catch (Balirwa 2007). The other main driver was the increase in nutrient input from the Lake Victoria surroundings, leading to instances of algae blooms and hypoxia. The deoxygenation created an environment which was not suitable for the cichlids, many of which inhabited lower water columns where the oxygen deficiency was most acute (Hecky et al. 1994). The increase in nutrient inputs also caused turbidity which contributed to the reduction of reproductive capacity among cichlids (Seehausen et al. 1997).

The underlying driver of both of these developments is the human population growth around the lake, accelerating fishery activities and off-shore developments such as deforestation and expansion of agriculture which fed the lake with nutrient run-offs (Ibid.). Another cause of the demise of the cichlids was the heavy rainfall events during the 1960s. This external shock destroyed littoral vegetation around the lake which had served as important spawning and nursery grounds for native species. This enabled another species, the Nile tilapia, to conquer some of these areas and outcompete cichlids (Kaufman 1992). At this time the system was resilient enough to avert a shift but these events were precursors to later developments. 

How the regime shift worked

Under the cichlid dominated regime, Lake Victoria was an ecosystem with high species diversity. By eating basically everything in the lake these cichlids performed tight internal recycling (Kaufman 1992) and the pelagic planktivorous and detritivorous cichlids occupied a significant role in protecting the system against the excess production of phytoplankton (Goldschmidt et al. 1993). This allowed allowed resilience against increased nutrient input. The dominance of the cichlids also suppressed other species, including the Nile perch. The cichlids fed upon Nile perch larvae and competed with Nile perch juveniles for space and food (Goudswaard et al. 2008). These dynamics might explain why it took the Nile perch decades to accomplish its virtual takeover of the lake; as long as the cichlids were abundant, the Nile perch reproduction was suppressed (Ibid.).

However, due to the combined threats of Nile perch predation, overfishing, and the increasing nutrient inputs, this changed. First, the overfishing severely reduced the cichlid population in certain areas. Once the cichlid stock was reduced the Nile perch juveniles were able to colonize the areas. From there on, the Nile perch population could grow, invade neighboring areas, reduce the cichlids, and open up new areas for the recruitment of Nile perch juveniles (Ibid.). In this new regime, the Nile perch was the dominator and cichlids then dominated. When the cichlids started to disappear, this situation was opportunistically exploited by other species, including native shrimps. In the absence of the cichlids the shrimp population grew massively and became the most important source of food for the Nile perch (Kaufman 1992, Goldschmidt et al. 1993).

The reduction of cichlids, in combination with the spike in nutrient input, in turn had detrimental effects on the nutrient recycling, resulting in hypoxia. Those cichlids which had inhabited the lower water columns, and had therefore avoided Nile perch, were forced to migrate to shallow waters to escape the hypoxic waters. In these shallow waters they became the target of Nile perch predation (Hecky et al. 1994). 

Impacts on ecosystem services and human well-being

Both before and after the regime shift, Lake Victoria has been providing important provisioning ecosystem services, primarily fisheries. Before the shift, these fisheries were run by small-scale fishermen and operators; women were largely involved in the business (Abila & Jansen 1997), and the fish was for local consumption. However, the Nile perch boom diminished the variety of native fish, and turned this food source into economically more valuable forms of fish meat (Geheb et al. 2008). Foreign investment brought processing plants to the lake's shores (Kaufman 1992), boosted fish export, and eventually turned the artisanal fishery into a large-scale international enterprise. Another provisioning ecosystem service, namely the provision of freshwater suffered from decreased water quality through the cichlids' disappearance (Kaufman 1992).

Cultural ecosystem services were gained in terms of (fishing) tourism but presumably lost in terms of ecosystem/biodiversity knowledge, and aesthetic values. Since the regime shift, the majority of local community members have been carrying out economic activities linked to the Nile Perch fishery. The livelihood for many has improved (Abila & Jansen 1997). However, income from the fishing industry has been unequally distributed (Geheb et al. 2008). Due to social gender inequalities mainly men have been drawing profits from the fisheries boom while women and children have often been victims of malnutrition which is high along the lake's shores (ibid.). Many women have been forced into prostitution which in turn has increased the number of HIV/Aids infections after the Nile perch boom (Appleton 2000). 

Management options

The Nile perch was introduced in Lake Victoria to improve the commercial fishing values (Balirwa et al. 2003). The social effects from this have had huge and diverse impacts on the local communities around the lake resulting in, on one side, a billion dollar export industry, and on the other side, malnutrition, unequally divided income, and increased spread of HIV/Aids (Béné & Merten 2007, Appleton 2000). Nothing was done to prevent the shift from the cichlid dominated regime to the Nile perch dominated regime in the 1980s. Currently there are many different projects that work across the Lake Victoria Basin. The Lake Victoria Basin Commission (LVBC) is an institution of the East African Community which coordinates the policy and management agenda for the region (LVBC 2011). The program works for local community participation, poverty reduction and environmental concerns. Health issues, especially HIV/Aids (LVFO 2011) and human well-being are the most important parts of many different projects working in the lake surroundings. Some projects in the Kenyan part of the Lake Victoria basin mentioned by Swallow 2009 are the TransVic project byWorld Agroforestry Center, the Western Kenya Integrated Ecosystem Management Project and Vi Agroforestry (Swallow 2003 and 2009). These are all focusing on land degradation and agroforestry as land use management methods which both reduce the nutrient input to improve the lake conditions and work for poverty reduction (ibid.). 

A return to a regime with low abundance of Nile perch is not the focus of management and action plans (Schindler et al. 1998, Kitchell 1997) since the economic value of the Nile perch is so important. The ecological focus is rather on restoration of biodiversity, the lake ecosystem services, and the sustainability of the fisheries in the lake. A sustainable fishing of Nile perch can be reached by the control of fishing practices(Seehausen et al. 1997a). A study by Schindler et al. in 1998 show that by using a minimum mesh size of 5-inches the Nile perch cannibalism and the predation of native species can be reduced by 44% at the same time as the catches of Nile perch is only reduced by 10%. The re-emergence of native cichlids is an important step in the lake management to restore biodiversity in the lake system. By continuing the fishing of Nile perch the species is held at a controlled level giving the cichlids an opportunity to return to the system. For this it is also of great importance to improve the lake conditions by reducing the leakage of nutrients into the lake e.g. through investments in sewage treatment and restoration of wetlands in the basin area (Balirwa et al. 2003).

 

 

Key References

  1. Xue C. 1993. Historical Changes in the Yellow River delta, China. Marine Geology 113, 321-329.

Citation

Henning Nolzen, Reinette (Oonsie) Biggs, Garry Peterson. Yellow River delta, China. In: Regime Shifts Database, www.regimeshifts.org. Last revised 2012-03-17 13:36:45 GMT.
Thursday, 15 March 2012 16:55

River Bollin, UK

Written by Reinette (Oonsie) Biggs

River Bollin, UK

Main Contributors:

Henning Nolzen

Other Contributors:

Reinette (Oonsie) Biggs, Garry Peterson

Summary

Several meander cutoffs occurred within a short time period between 1999 and 2002 on the River Bollin in North West England. Although strong flood events were the direct cause of the cut-offs, several hypotheses exist to explain the underlying reasons why the River Bollin became susceptible to such flooding impacts. One explanation is a change in discharge because of changes in rainfall characteristics, population growth, and land use change. Another hypothesis focuses on the occurrence of exceptionally strong flood events. Natural evolution of meanders without chaotic behaviour might also explain the cutoffs. Furthermore, there were some artificial cutoffs in 1990 when changes in the river course threatened a public footpath. 

Type of regime shift

Ecosystem type

  • Freshwater lakes & rivers

Land uses

  • Urban
  • Fisheries

Spatial scale of the case study

  • Local/landscape (e.g. lake, catchment, community)

Continent or Ocean

  • Europe

Region

  • North West England, United Kingdom

Countries

  • United Kingdom

Locate with Google Map

Alternate regimes

Cichlid dominated regime (1950s – 1980s)

The regime was characterized by a lake of high biodiversity dominated by different species of native haplochromine cichlids (Balirwa et al. 2003; UNEP 2010). Cichlids span over many different trophic levels and represent nearly all different functional groups in Lake Victoria (UNEP 2010). In this regime the lake was less eutrophic compared to the current regime and thus less turbid. Nile perch was already introduced to the lake but populations remained low.

In the lake basin there were many local communities living on subsistence farming and small-scale fishing (Swallow 2009). The native fish species provided food for the local communities and the fishing for native cichlids was non-commercial but still population growth in the region put a large pressure on the native fish stocks (Seehausen et al. 1997).

Nile perch-dominated regime (From 1980s)

In this current regime the system has much reduced biodiverse lake with high abundance of only three species, the dominant Nile perch Lates niloticus, Nile tilapia Oreochromis niloticus (Balirwa et al. 2003), and a native cyprinid Rastrineobola argentea (UNEP 2010). The cyprinid is competing for the same resources as some cichlids (Matsuishi et al. 2006) and thus became very abundant once the cichlids disappeared. This low diversity makes the system vulnerable to disturbances (Balirwa et al. 2003; UNEP 2010). Eutrophication is an ever increasing problem resulting in algae blooms, turbidity, and hypoxia (Balirwa et al. 2003), all of which are undesirable conditions for the native species.

The fishing of Nile perch created a global market for fish export. The fishing industries involved many from the local communities and there was an increase in income for those in the Nile perch business. However, the changes brought many social problems emerging from unequal distribution of the increased income (Geheb et al. 2008). 

Drivers and causes of the regime shift

The apparent extinction of several hundreds of cichlid species was caused by Nile perch predation (Goudswaard et al. 2008). However, this event was preceded by drivers that weakened the cichlid population and opened up the field for the Nile perch. One of the main drivers was the increased pressure on the Lake Victoria cichlids by fisheries. At the beginning of the 1980s, cichlids accounted for more than 90 percent of the catch (Balirwa 2007). The other main driver was the increase in nutrient input from the Lake Victoria surroundings, leading to instances of algae blooms and hypoxia. The deoxygenation created an environment which was not suitable for the cichlids, many of which inhabited lower water columns where the oxygen deficiency was most acute (Hecky et al. 1994). The increase in nutrient inputs also caused turbidity which contributed to the reduction of reproductive capacity among cichlids (Seehausen et al. 1997).

The underlying driver of both of these developments is the human population growth around the lake, accelerating fishery activities and off-shore developments such as deforestation and expansion of agriculture which fed the lake with nutrient run-offs (Ibid.). Another cause of the demise of the cichlids was the heavy rainfall events during the 1960s. This external shock destroyed littoral vegetation around the lake which had served as important spawning and nursery grounds for native species. This enabled another species, the Nile tilapia, to conquer some of these areas and outcompete cichlids (Kaufman 1992). At this time the system was resilient enough to avert a shift but these events were precursors to later developments. 

How the regime shift worked

Under the cichlid dominated regime, Lake Victoria was an ecosystem with high species diversity. By eating basically everything in the lake these cichlids performed tight internal recycling (Kaufman 1992) and the pelagic planktivorous and detritivorous cichlids occupied a significant role in protecting the system against the excess production of phytoplankton (Goldschmidt et al. 1993). This allowed allowed resilience against increased nutrient input. The dominance of the cichlids also suppressed other species, including the Nile perch. The cichlids fed upon Nile perch larvae and competed with Nile perch juveniles for space and food (Goudswaard et al. 2008). These dynamics might explain why it took the Nile perch decades to accomplish its virtual takeover of the lake; as long as the cichlids were abundant, the Nile perch reproduction was suppressed (Ibid.).

However, due to the combined threats of Nile perch predation, overfishing, and the increasing nutrient inputs, this changed. First, the overfishing severely reduced the cichlid population in certain areas. Once the cichlid stock was reduced the Nile perch juveniles were able to colonize the areas. From there on, the Nile perch population could grow, invade neighboring areas, reduce the cichlids, and open up new areas for the recruitment of Nile perch juveniles (Ibid.). In this new regime, the Nile perch was the dominator and cichlids then dominated. When the cichlids started to disappear, this situation was opportunistically exploited by other species, including native shrimps. In the absence of the cichlids the shrimp population grew massively and became the most important source of food for the Nile perch (Kaufman 1992, Goldschmidt et al. 1993).

The reduction of cichlids, in combination with the spike in nutrient input, in turn had detrimental effects on the nutrient recycling, resulting in hypoxia. Those cichlids which had inhabited the lower water columns, and had therefore avoided Nile perch, were forced to migrate to shallow waters to escape the hypoxic waters. In these shallow waters they became the target of Nile perch predation (Hecky et al. 1994). 

Impacts on ecosystem services and human well-being

Both before and after the regime shift, Lake Victoria has been providing important provisioning ecosystem services, primarily fisheries. Before the shift, these fisheries were run by small-scale fishermen and operators; women were largely involved in the business (Abila & Jansen 1997), and the fish was for local consumption. However, the Nile perch boom diminished the variety of native fish, and turned this food source into economically more valuable forms of fish meat (Geheb et al. 2008). Foreign investment brought processing plants to the lake's shores (Kaufman 1992), boosted fish export, and eventually turned the artisanal fishery into a large-scale international enterprise. Another provisioning ecosystem service, namely the provision of freshwater suffered from decreased water quality through the cichlids' disappearance (Kaufman 1992).

Cultural ecosystem services were gained in terms of (fishing) tourism but presumably lost in terms of ecosystem/biodiversity knowledge, and aesthetic values. Since the regime shift, the majority of local community members have been carrying out economic activities linked to the Nile Perch fishery. The livelihood for many has improved (Abila & Jansen 1997). However, income from the fishing industry has been unequally distributed (Geheb et al. 2008). Due to social gender inequalities mainly men have been drawing profits from the fisheries boom while women and children have often been victims of malnutrition which is high along the lake's shores (ibid.). Many women have been forced into prostitution which in turn has increased the number of HIV/Aids infections after the Nile perch boom (Appleton 2000). 

Management options

The Nile perch was introduced in Lake Victoria to improve the commercial fishing values (Balirwa et al. 2003). The social effects from this have had huge and diverse impacts on the local communities around the lake resulting in, on one side, a billion dollar export industry, and on the other side, malnutrition, unequally divided income, and increased spread of HIV/Aids (Béné & Merten 2007, Appleton 2000). Nothing was done to prevent the shift from the cichlid dominated regime to the Nile perch dominated regime in the 1980s. Currently there are many different projects that work across the Lake Victoria Basin. The Lake Victoria Basin Commission (LVBC) is an institution of the East African Community which coordinates the policy and management agenda for the region (LVBC 2011). The program works for local community participation, poverty reduction and environmental concerns. Health issues, especially HIV/Aids (LVFO 2011) and human well-being are the most important parts of many different projects working in the lake surroundings. Some projects in the Kenyan part of the Lake Victoria basin mentioned by Swallow 2009 are the TransVic project byWorld Agroforestry Center, the Western Kenya Integrated Ecosystem Management Project and Vi Agroforestry (Swallow 2003 and 2009). These are all focusing on land degradation and agroforestry as land use management methods which both reduce the nutrient input to improve the lake conditions and work for poverty reduction (ibid.). 

A return to a regime with low abundance of Nile perch is not the focus of management and action plans (Schindler et al. 1998, Kitchell 1997) since the economic value of the Nile perch is so important. The ecological focus is rather on restoration of biodiversity, the lake ecosystem services, and the sustainability of the fisheries in the lake. A sustainable fishing of Nile perch can be reached by the control of fishing practices(Seehausen et al. 1997a). A study by Schindler et al. in 1998 show that by using a minimum mesh size of 5-inches the Nile perch cannibalism and the predation of native species can be reduced by 44% at the same time as the catches of Nile perch is only reduced by 10%. The re-emergence of native cichlids is an important step in the lake management to restore biodiversity in the lake system. By continuing the fishing of Nile perch the species is held at a controlled level giving the cichlids an opportunity to return to the system. For this it is also of great importance to improve the lake conditions by reducing the leakage of nutrients into the lake e.g. through investments in sewage treatment and restoration of wetlands in the basin area (Balirwa et al. 2003).

 

 

Alternate regimes

Cichlid dominated regime (1950s – 1980s)

The regime was characterized by a lake of high biodiversity dominated by different species of native haplochromine cichlids (Balirwa et al. 2003; UNEP 2010). Cichlids span over many different trophic levels and represent nearly all different functional groups in Lake Victoria (UNEP 2010). In this regime the lake was less eutrophic compared to the current regime and thus less turbid. Nile perch was already introduced to the lake but populations remained low.

In the lake basin there were many local communities living on subsistence farming and small-scale fishing (Swallow 2009). The native fish species provided food for the local communities and the fishing for native cichlids was non-commercial but still population growth in the region put a large pressure on the native fish stocks (Seehausen et al. 1997).

Nile perch-dominated regime (From 1980s)

In this current regime the system has much reduced biodiverse lake with high abundance of only three species, the dominant Nile perch Lates niloticus, Nile tilapia Oreochromis niloticus (Balirwa et al. 2003), and a native cyprinid Rastrineobola argentea (UNEP 2010). The cyprinid is competing for the same resources as some cichlids (Matsuishi et al. 2006) and thus became very abundant once the cichlids disappeared. This low diversity makes the system vulnerable to disturbances (Balirwa et al. 2003; UNEP 2010). Eutrophication is an ever increasing problem resulting in algae blooms, turbidity, and hypoxia (Balirwa et al. 2003), all of which are undesirable conditions for the native species.

The fishing of Nile perch created a global market for fish export. The fishing industries involved many from the local communities and there was an increase in income for those in the Nile perch business. However, the changes brought many social problems emerging from unequal distribution of the increased income (Geheb et al. 2008). 

Drivers and causes of the regime shift

The apparent extinction of several hundreds of cichlid species was caused by Nile perch predation (Goudswaard et al. 2008). However, this event was preceded by drivers that weakened the cichlid population and opened up the field for the Nile perch. One of the main drivers was the increased pressure on the Lake Victoria cichlids by fisheries. At the beginning of the 1980s, cichlids accounted for more than 90 percent of the catch (Balirwa 2007). The other main driver was the increase in nutrient input from the Lake Victoria surroundings, leading to instances of algae blooms and hypoxia. The deoxygenation created an environment which was not suitable for the cichlids, many of which inhabited lower water columns where the oxygen deficiency was most acute (Hecky et al. 1994). The increase in nutrient inputs also caused turbidity which contributed to the reduction of reproductive capacity among cichlids (Seehausen et al. 1997).

The underlying driver of both of these developments is the human population growth around the lake, accelerating fishery activities and off-shore developments such as deforestation and expansion of agriculture which fed the lake with nutrient run-offs (Ibid.). Another cause of the demise of the cichlids was the heavy rainfall events during the 1960s. This external shock destroyed littoral vegetation around the lake which had served as important spawning and nursery grounds for native species. This enabled another species, the Nile tilapia, to conquer some of these areas and outcompete cichlids (Kaufman 1992). At this time the system was resilient enough to avert a shift but these events were precursors to later developments. 

How the regime shift worked

Under the cichlid dominated regime, Lake Victoria was an ecosystem with high species diversity. By eating basically everything in the lake these cichlids performed tight internal recycling (Kaufman 1992) and the pelagic planktivorous and detritivorous cichlids occupied a significant role in protecting the system against the excess production of phytoplankton (Goldschmidt et al. 1993). This allowed allowed resilience against increased nutrient input. The dominance of the cichlids also suppressed other species, including the Nile perch. The cichlids fed upon Nile perch larvae and competed with Nile perch juveniles for space and food (Goudswaard et al. 2008). These dynamics might explain why it took the Nile perch decades to accomplish its virtual takeover of the lake; as long as the cichlids were abundant, the Nile perch reproduction was suppressed (Ibid.).

However, due to the combined threats of Nile perch predation, overfishing, and the increasing nutrient inputs, this changed. First, the overfishing severely reduced the cichlid population in certain areas. Once the cichlid stock was reduced the Nile perch juveniles were able to colonize the areas. From there on, the Nile perch population could grow, invade neighboring areas, reduce the cichlids, and open up new areas for the recruitment of Nile perch juveniles (Ibid.). In this new regime, the Nile perch was the dominator and cichlids then dominated. When the cichlids started to disappear, this situation was opportunistically exploited by other species, including native shrimps. In the absence of the cichlids the shrimp population grew massively and became the most important source of food for the Nile perch (Kaufman 1992, Goldschmidt et al. 1993).

The reduction of cichlids, in combination with the spike in nutrient input, in turn had detrimental effects on the nutrient recycling, resulting in hypoxia. Those cichlids which had inhabited the lower water columns, and had therefore avoided Nile perch, were forced to migrate to shallow waters to escape the hypoxic waters. In these shallow waters they became the target of Nile perch predation (Hecky et al. 1994). 

Impacts on ecosystem services and human well-being

Both before and after the regime shift, Lake Victoria has been providing important provisioning ecosystem services, primarily fisheries. Before the shift, these fisheries were run by small-scale fishermen and operators; women were largely involved in the business (Abila & Jansen 1997), and the fish was for local consumption. However, the Nile perch boom diminished the variety of native fish, and turned this food source into economically more valuable forms of fish meat (Geheb et al. 2008). Foreign investment brought processing plants to the lake's shores (Kaufman 1992), boosted fish export, and eventually turned the artisanal fishery into a large-scale international enterprise. Another provisioning ecosystem service, namely the provision of freshwater suffered from decreased water quality through the cichlids' disappearance (Kaufman 1992).

Cultural ecosystem services were gained in terms of (fishing) tourism but presumably lost in terms of ecosystem/biodiversity knowledge, and aesthetic values. Since the regime shift, the majority of local community members have been carrying out economic activities linked to the Nile Perch fishery. The livelihood for many has improved (Abila & Jansen 1997). However, income from the fishing industry has been unequally distributed (Geheb et al. 2008). Due to social gender inequalities mainly men have been drawing profits from the fisheries boom while women and children have often been victims of malnutrition which is high along the lake's shores (ibid.). Many women have been forced into prostitution which in turn has increased the number of HIV/Aids infections after the Nile perch boom (Appleton 2000). 

Management options

The Nile perch was introduced in Lake Victoria to improve the commercial fishing values (Balirwa et al. 2003). The social effects from this have had huge and diverse impacts on the local communities around the lake resulting in, on one side, a billion dollar export industry, and on the other side, malnutrition, unequally divided income, and increased spread of HIV/Aids (Béné & Merten 2007, Appleton 2000). Nothing was done to prevent the shift from the cichlid dominated regime to the Nile perch dominated regime in the 1980s. Currently there are many different projects that work across the Lake Victoria Basin. The Lake Victoria Basin Commission (LVBC) is an institution of the East African Community which coordinates the policy and management agenda for the region (LVBC 2011). The program works for local community participation, poverty reduction and environmental concerns. Health issues, especially HIV/Aids (LVFO 2011) and human well-being are the most important parts of many different projects working in the lake surroundings. Some projects in the Kenyan part of the Lake Victoria basin mentioned by Swallow 2009 are the TransVic project byWorld Agroforestry Center, the Western Kenya Integrated Ecosystem Management Project and Vi Agroforestry (Swallow 2003 and 2009). These are all focusing on land degradation and agroforestry as land use management methods which both reduce the nutrient input to improve the lake conditions and work for poverty reduction (ibid.). 

A return to a regime with low abundance of Nile perch is not the focus of management and action plans (Schindler et al. 1998, Kitchell 1997) since the economic value of the Nile perch is so important. The ecological focus is rather on restoration of biodiversity, the lake ecosystem services, and the sustainability of the fisheries in the lake. A sustainable fishing of Nile perch can be reached by the control of fishing practices(Seehausen et al. 1997a). A study by Schindler et al. in 1998 show that by using a minimum mesh size of 5-inches the Nile perch cannibalism and the predation of native species can be reduced by 44% at the same time as the catches of Nile perch is only reduced by 10%. The re-emergence of native cichlids is an important step in the lake management to restore biodiversity in the lake system. By continuing the fishing of Nile perch the species is held at a controlled level giving the cichlids an opportunity to return to the system. For this it is also of great importance to improve the lake conditions by reducing the leakage of nutrients into the lake e.g. through investments in sewage treatment and restoration of wetlands in the basin area (Balirwa et al. 2003).

 

 

Key References

  1. Hooke JM 2003. River meander behaviour and instability: a framework for analysis, Transactions of the Institute of British Geographers 28, Issue 2, 238–253.
  2. Hooke JM. 2004. Cutoffs galore! Occurrence and causes of multiple cutoffs on a meandering river. Geomorphology 61, 225-238.

Citation

Henning Nolzen, Reinette (Oonsie) Biggs, Garry Peterson. River Bollin, UK. In: Regime Shifts Database, www.regimeshifts.org. Last revised 2012-03-19 08:07:10 GMT.
Thursday, 15 March 2012 16:25

Ucayali River, Peru

Written by Reinette (Oonsie) Biggs

Ucayali River, Peru

Main Contributors:

Henning Nolzen

Other Contributors:

Reinette (Oonsie) Biggs, Garry Peterson

Summary

In 1997, a river channel position shift, the so-called Masisea cutoff, occurred at the Ucayali River in Peru. A 71 km meander loop was cut-off and created a 33-47 km2 large oxbow lake. Besides flood events, especially those in 1997 when the cutoff occurred, the shift was mainly driven by human actions from the late 1980s onward. Residents from nearby upstream villages removed debris and cut vegetation along a small flood channel across the meander neck (where the cutoff took place) in order to improve transit and to establish a toll system. From the 1900s the channel and its connection to a floodplain lake have been used as a shortcut for canoes. A third reason for the cut off of vegetation was to facilitate bank erosion. Later, the channel was systematically maintained and widened with machetes, axes and shovels. Shallow, circular pits were excavated that acted as scour holes and in 1997 even a tractor was used to widen the entrance to the channel. The Masisea cut-off had significant impacts on the ecology and the economy upstream and downstream of the location at which it occurred. Upstream impacts consisted of a decrease in flood events, flood levels, travel time and transportation costs, which led to new economic opportunities such as changes in subsistence crops (e.g. plantain and maize) and cash crops that generated a higher income for people living upstream (e.g. papaya). In addition, the new economic opportunities upstream supported in-migration. However, downstream impacts consisted of an increase in flood events, flood levels, riverbed aggradation, bank erosion, lateral channel shifts and stranded communities. These impacts in turn led to a heightened vulnerability in floodplain agriculture, so that people increased their reliance on fishing and shifted their land-use from perennial to annual crops. Furthermore, the negative impacts led to upstream migration. 

Type of regime shift

Ecosystem type

  • Freshwater lakes & rivers

Land uses

  • Small-scale subsistence crop cultivation
  • Fisheries

Spatial scale of the case study

  • Local/landscape (e.g. lake, catchment, community)

Continent or Ocean

  • South America

Region

  • Ucayali, Peru

Countries

  • Peru

Locate with Google Map

Alternate regimes

Cichlid dominated regime (1950s – 1980s)

The regime was characterized by a lake of high biodiversity dominated by different species of native haplochromine cichlids (Balirwa et al. 2003; UNEP 2010). Cichlids span over many different trophic levels and represent nearly all different functional groups in Lake Victoria (UNEP 2010). In this regime the lake was less eutrophic compared to the current regime and thus less turbid. Nile perch was already introduced to the lake but populations remained low.

In the lake basin there were many local communities living on subsistence farming and small-scale fishing (Swallow 2009). The native fish species provided food for the local communities and the fishing for native cichlids was non-commercial but still population growth in the region put a large pressure on the native fish stocks (Seehausen et al. 1997).

Nile perch-dominated regime (From 1980s)

In this current regime the system has much reduced biodiverse lake with high abundance of only three species, the dominant Nile perch Lates niloticus, Nile tilapia Oreochromis niloticus (Balirwa et al. 2003), and a native cyprinid Rastrineobola argentea (UNEP 2010). The cyprinid is competing for the same resources as some cichlids (Matsuishi et al. 2006) and thus became very abundant once the cichlids disappeared. This low diversity makes the system vulnerable to disturbances (Balirwa et al. 2003; UNEP 2010). Eutrophication is an ever increasing problem resulting in algae blooms, turbidity, and hypoxia (Balirwa et al. 2003), all of which are undesirable conditions for the native species.

The fishing of Nile perch created a global market for fish export. The fishing industries involved many from the local communities and there was an increase in income for those in the Nile perch business. However, the changes brought many social problems emerging from unequal distribution of the increased income (Geheb et al. 2008). 

Drivers and causes of the regime shift

The apparent extinction of several hundreds of cichlid species was caused by Nile perch predation (Goudswaard et al. 2008). However, this event was preceded by drivers that weakened the cichlid population and opened up the field for the Nile perch. One of the main drivers was the increased pressure on the Lake Victoria cichlids by fisheries. At the beginning of the 1980s, cichlids accounted for more than 90 percent of the catch (Balirwa 2007). The other main driver was the increase in nutrient input from the Lake Victoria surroundings, leading to instances of algae blooms and hypoxia. The deoxygenation created an environment which was not suitable for the cichlids, many of which inhabited lower water columns where the oxygen deficiency was most acute (Hecky et al. 1994). The increase in nutrient inputs also caused turbidity which contributed to the reduction of reproductive capacity among cichlids (Seehausen et al. 1997).

The underlying driver of both of these developments is the human population growth around the lake, accelerating fishery activities and off-shore developments such as deforestation and expansion of agriculture which fed the lake with nutrient run-offs (Ibid.). Another cause of the demise of the cichlids was the heavy rainfall events during the 1960s. This external shock destroyed littoral vegetation around the lake which had served as important spawning and nursery grounds for native species. This enabled another species, the Nile tilapia, to conquer some of these areas and outcompete cichlids (Kaufman 1992). At this time the system was resilient enough to avert a shift but these events were precursors to later developments. 

How the regime shift worked

Under the cichlid dominated regime, Lake Victoria was an ecosystem with high species diversity. By eating basically everything in the lake these cichlids performed tight internal recycling (Kaufman 1992) and the pelagic planktivorous and detritivorous cichlids occupied a significant role in protecting the system against the excess production of phytoplankton (Goldschmidt et al. 1993). This allowed allowed resilience against increased nutrient input. The dominance of the cichlids also suppressed other species, including the Nile perch. The cichlids fed upon Nile perch larvae and competed with Nile perch juveniles for space and food (Goudswaard et al. 2008). These dynamics might explain why it took the Nile perch decades to accomplish its virtual takeover of the lake; as long as the cichlids were abundant, the Nile perch reproduction was suppressed (Ibid.).

However, due to the combined threats of Nile perch predation, overfishing, and the increasing nutrient inputs, this changed. First, the overfishing severely reduced the cichlid population in certain areas. Once the cichlid stock was reduced the Nile perch juveniles were able to colonize the areas. From there on, the Nile perch population could grow, invade neighboring areas, reduce the cichlids, and open up new areas for the recruitment of Nile perch juveniles (Ibid.). In this new regime, the Nile perch was the dominator and cichlids then dominated. When the cichlids started to disappear, this situation was opportunistically exploited by other species, including native shrimps. In the absence of the cichlids the shrimp population grew massively and became the most important source of food for the Nile perch (Kaufman 1992, Goldschmidt et al. 1993).

The reduction of cichlids, in combination with the spike in nutrient input, in turn had detrimental effects on the nutrient recycling, resulting in hypoxia. Those cichlids which had inhabited the lower water columns, and had therefore avoided Nile perch, were forced to migrate to shallow waters to escape the hypoxic waters. In these shallow waters they became the target of Nile perch predation (Hecky et al. 1994). 

Impacts on ecosystem services and human well-being

Both before and after the regime shift, Lake Victoria has been providing important provisioning ecosystem services, primarily fisheries. Before the shift, these fisheries were run by small-scale fishermen and operators; women were largely involved in the business (Abila & Jansen 1997), and the fish was for local consumption. However, the Nile perch boom diminished the variety of native fish, and turned this food source into economically more valuable forms of fish meat (Geheb et al. 2008). Foreign investment brought processing plants to the lake's shores (Kaufman 1992), boosted fish export, and eventually turned the artisanal fishery into a large-scale international enterprise. Another provisioning ecosystem service, namely the provision of freshwater suffered from decreased water quality through the cichlids' disappearance (Kaufman 1992).

Cultural ecosystem services were gained in terms of (fishing) tourism but presumably lost in terms of ecosystem/biodiversity knowledge, and aesthetic values. Since the regime shift, the majority of local community members have been carrying out economic activities linked to the Nile Perch fishery. The livelihood for many has improved (Abila & Jansen 1997). However, income from the fishing industry has been unequally distributed (Geheb et al. 2008). Due to social gender inequalities mainly men have been drawing profits from the fisheries boom while women and children have often been victims of malnutrition which is high along the lake's shores (ibid.). Many women have been forced into prostitution which in turn has increased the number of HIV/Aids infections after the Nile perch boom (Appleton 2000). 

Management options

The Nile perch was introduced in Lake Victoria to improve the commercial fishing values (Balirwa et al. 2003). The social effects from this have had huge and diverse impacts on the local communities around the lake resulting in, on one side, a billion dollar export industry, and on the other side, malnutrition, unequally divided income, and increased spread of HIV/Aids (Béné & Merten 2007, Appleton 2000). Nothing was done to prevent the shift from the cichlid dominated regime to the Nile perch dominated regime in the 1980s. Currently there are many different projects that work across the Lake Victoria Basin. The Lake Victoria Basin Commission (LVBC) is an institution of the East African Community which coordinates the policy and management agenda for the region (LVBC 2011). The program works for local community participation, poverty reduction and environmental concerns. Health issues, especially HIV/Aids (LVFO 2011) and human well-being are the most important parts of many different projects working in the lake surroundings. Some projects in the Kenyan part of the Lake Victoria basin mentioned by Swallow 2009 are the TransVic project byWorld Agroforestry Center, the Western Kenya Integrated Ecosystem Management Project and Vi Agroforestry (Swallow 2003 and 2009). These are all focusing on land degradation and agroforestry as land use management methods which both reduce the nutrient input to improve the lake conditions and work for poverty reduction (ibid.). 

A return to a regime with low abundance of Nile perch is not the focus of management and action plans (Schindler et al. 1998, Kitchell 1997) since the economic value of the Nile perch is so important. The ecological focus is rather on restoration of biodiversity, the lake ecosystem services, and the sustainability of the fisheries in the lake. A sustainable fishing of Nile perch can be reached by the control of fishing practices(Seehausen et al. 1997a). A study by Schindler et al. in 1998 show that by using a minimum mesh size of 5-inches the Nile perch cannibalism and the predation of native species can be reduced by 44% at the same time as the catches of Nile perch is only reduced by 10%. The re-emergence of native cichlids is an important step in the lake management to restore biodiversity in the lake system. By continuing the fishing of Nile perch the species is held at a controlled level giving the cichlids an opportunity to return to the system. For this it is also of great importance to improve the lake conditions by reducing the leakage of nutrients into the lake e.g. through investments in sewage treatment and restoration of wetlands in the basin area (Balirwa et al. 2003).

 

 

Alternate regimes

Cichlid dominated regime (1950s – 1980s)

The regime was characterized by a lake of high biodiversity dominated by different species of native haplochromine cichlids (Balirwa et al. 2003; UNEP 2010). Cichlids span over many different trophic levels and represent nearly all different functional groups in Lake Victoria (UNEP 2010). In this regime the lake was less eutrophic compared to the current regime and thus less turbid. Nile perch was already introduced to the lake but populations remained low.

In the lake basin there were many local communities living on subsistence farming and small-scale fishing (Swallow 2009). The native fish species provided food for the local communities and the fishing for native cichlids was non-commercial but still population growth in the region put a large pressure on the native fish stocks (Seehausen et al. 1997).

Nile perch-dominated regime (From 1980s)

In this current regime the system has much reduced biodiverse lake with high abundance of only three species, the dominant Nile perch Lates niloticus, Nile tilapia Oreochromis niloticus (Balirwa et al. 2003), and a native cyprinid Rastrineobola argentea (UNEP 2010). The cyprinid is competing for the same resources as some cichlids (Matsuishi et al. 2006) and thus became very abundant once the cichlids disappeared. This low diversity makes the system vulnerable to disturbances (Balirwa et al. 2003; UNEP 2010). Eutrophication is an ever increasing problem resulting in algae blooms, turbidity, and hypoxia (Balirwa et al. 2003), all of which are undesirable conditions for the native species.

The fishing of Nile perch created a global market for fish export. The fishing industries involved many from the local communities and there was an increase in income for those in the Nile perch business. However, the changes brought many social problems emerging from unequal distribution of the increased income (Geheb et al. 2008). 

Drivers and causes of the regime shift

The apparent extinction of several hundreds of cichlid species was caused by Nile perch predation (Goudswaard et al. 2008). However, this event was preceded by drivers that weakened the cichlid population and opened up the field for the Nile perch. One of the main drivers was the increased pressure on the Lake Victoria cichlids by fisheries. At the beginning of the 1980s, cichlids accounted for more than 90 percent of the catch (Balirwa 2007). The other main driver was the increase in nutrient input from the Lake Victoria surroundings, leading to instances of algae blooms and hypoxia. The deoxygenation created an environment which was not suitable for the cichlids, many of which inhabited lower water columns where the oxygen deficiency was most acute (Hecky et al. 1994). The increase in nutrient inputs also caused turbidity which contributed to the reduction of reproductive capacity among cichlids (Seehausen et al. 1997).

The underlying driver of both of these developments is the human population growth around the lake, accelerating fishery activities and off-shore developments such as deforestation and expansion of agriculture which fed the lake with nutrient run-offs (Ibid.). Another cause of the demise of the cichlids was the heavy rainfall events during the 1960s. This external shock destroyed littoral vegetation around the lake which had served as important spawning and nursery grounds for native species. This enabled another species, the Nile tilapia, to conquer some of these areas and outcompete cichlids (Kaufman 1992). At this time the system was resilient enough to avert a shift but these events were precursors to later developments. 

How the regime shift worked

Under the cichlid dominated regime, Lake Victoria was an ecosystem with high species diversity. By eating basically everything in the lake these cichlids performed tight internal recycling (Kaufman 1992) and the pelagic planktivorous and detritivorous cichlids occupied a significant role in protecting the system against the excess production of phytoplankton (Goldschmidt et al. 1993). This allowed allowed resilience against increased nutrient input. The dominance of the cichlids also suppressed other species, including the Nile perch. The cichlids fed upon Nile perch larvae and competed with Nile perch juveniles for space and food (Goudswaard et al. 2008). These dynamics might explain why it took the Nile perch decades to accomplish its virtual takeover of the lake; as long as the cichlids were abundant, the Nile perch reproduction was suppressed (Ibid.).

However, due to the combined threats of Nile perch predation, overfishing, and the increasing nutrient inputs, this changed. First, the overfishing severely reduced the cichlid population in certain areas. Once the cichlid stock was reduced the Nile perch juveniles were able to colonize the areas. From there on, the Nile perch population could grow, invade neighboring areas, reduce the cichlids, and open up new areas for the recruitment of Nile perch juveniles (Ibid.). In this new regime, the Nile perch was the dominator and cichlids then dominated. When the cichlids started to disappear, this situation was opportunistically exploited by other species, including native shrimps. In the absence of the cichlids the shrimp population grew massively and became the most important source of food for the Nile perch (Kaufman 1992, Goldschmidt et al. 1993).

The reduction of cichlids, in combination with the spike in nutrient input, in turn had detrimental effects on the nutrient recycling, resulting in hypoxia. Those cichlids which had inhabited the lower water columns, and had therefore avoided Nile perch, were forced to migrate to shallow waters to escape the hypoxic waters. In these shallow waters they became the target of Nile perch predation (Hecky et al. 1994). 

Impacts on ecosystem services and human well-being

Both before and after the regime shift, Lake Victoria has been providing important provisioning ecosystem services, primarily fisheries. Before the shift, these fisheries were run by small-scale fishermen and operators; women were largely involved in the business (Abila & Jansen 1997), and the fish was for local consumption. However, the Nile perch boom diminished the variety of native fish, and turned this food source into economically more valuable forms of fish meat (Geheb et al. 2008). Foreign investment brought processing plants to the lake's shores (Kaufman 1992), boosted fish export, and eventually turned the artisanal fishery into a large-scale international enterprise. Another provisioning ecosystem service, namely the provision of freshwater suffered from decreased water quality through the cichlids' disappearance (Kaufman 1992).

Cultural ecosystem services were gained in terms of (fishing) tourism but presumably lost in terms of ecosystem/biodiversity knowledge, and aesthetic values. Since the regime shift, the majority of local community members have been carrying out economic activities linked to the Nile Perch fishery. The livelihood for many has improved (Abila & Jansen 1997). However, income from the fishing industry has been unequally distributed (Geheb et al. 2008). Due to social gender inequalities mainly men have been drawing profits from the fisheries boom while women and children have often been victims of malnutrition which is high along the lake's shores (ibid.). Many women have been forced into prostitution which in turn has increased the number of HIV/Aids infections after the Nile perch boom (Appleton 2000). 

Management options

The Nile perch was introduced in Lake Victoria to improve the commercial fishing values (Balirwa et al. 2003). The social effects from this have had huge and diverse impacts on the local communities around the lake resulting in, on one side, a billion dollar export industry, and on the other side, malnutrition, unequally divided income, and increased spread of HIV/Aids (Béné & Merten 2007, Appleton 2000). Nothing was done to prevent the shift from the cichlid dominated regime to the Nile perch dominated regime in the 1980s. Currently there are many different projects that work across the Lake Victoria Basin. The Lake Victoria Basin Commission (LVBC) is an institution of the East African Community which coordinates the policy and management agenda for the region (LVBC 2011). The program works for local community participation, poverty reduction and environmental concerns. Health issues, especially HIV/Aids (LVFO 2011) and human well-being are the most important parts of many different projects working in the lake surroundings. Some projects in the Kenyan part of the Lake Victoria basin mentioned by Swallow 2009 are the TransVic project byWorld Agroforestry Center, the Western Kenya Integrated Ecosystem Management Project and Vi Agroforestry (Swallow 2003 and 2009). These are all focusing on land degradation and agroforestry as land use management methods which both reduce the nutrient input to improve the lake conditions and work for poverty reduction (ibid.). 

A return to a regime with low abundance of Nile perch is not the focus of management and action plans (Schindler et al. 1998, Kitchell 1997) since the economic value of the Nile perch is so important. The ecological focus is rather on restoration of biodiversity, the lake ecosystem services, and the sustainability of the fisheries in the lake. A sustainable fishing of Nile perch can be reached by the control of fishing practices(Seehausen et al. 1997a). A study by Schindler et al. in 1998 show that by using a minimum mesh size of 5-inches the Nile perch cannibalism and the predation of native species can be reduced by 44% at the same time as the catches of Nile perch is only reduced by 10%. The re-emergence of native cichlids is an important step in the lake management to restore biodiversity in the lake system. By continuing the fishing of Nile perch the species is held at a controlled level giving the cichlids an opportunity to return to the system. For this it is also of great importance to improve the lake conditions by reducing the leakage of nutrients into the lake e.g. through investments in sewage treatment and restoration of wetlands in the basin area (Balirwa et al. 2003).

 

 

Key References

  1. Coomes OT, Abizaid C, Lapointe M. 2009. Human Modification of a Large Meandering Amazonian River: Genesis, Ecological and Economic Consequences of The Masisea Cutoff on the Central Ucayali, Peru. Ambio 38, No.3, 130-134.

Citation

Henning Nolzen, Reinette (Oonsie) Biggs, Garry Peterson. Ucayali River, Peru. In: Regime Shifts Database, www.regimeshifts.org. Last revised 2012-03-19 07:31:20 GMT.

Lake Veluwemeer & Lake Wolderwijd, Netherlands

Main Contributors:

Henning Nolzen

Other Contributors:

Reinette (Oonsie) Biggs, Garry Peterson

Summary

Lake Veluwemeer and Lake Wolderwijd are located in the Netherlands between the provinces Gelderland and Flevoland. They were created in 1957 (Veluwemeer) and 1969 (Wolderwijd) for the purpose of serving as flood polders. Both lakes are shallow and have an average water depth of 1.5 meters. They have been eutrophic since 1957 and 1969. This case study deals with the regime shift from a submerged plant dominated system of Potamogeton pectinatus and Potamogeton perfoliatus to 'meadows' of Charophytes, (especially Chara spp.) in Lake Veluwemeer and Lake Wolderwijd that happened between 1987 and 1993. Potamogeton pectinatus, better known as fennel pondweed, is a submerged plant that has 2 mm wide, dense, long and linear leaves. Potamogeton perfoliatus, also known as clasping-leaf pondweed, is a submerged plant with oval, translucent leaves with no stalk that can be up to 8 cm long. Charophytes are a division of green freshwater algaes that have large thalli (which means they have no organized and distinct parts such as leafs, roots or stems) which can grow up to 120 cm. Chara spp., also known as Stonewort, is a rapidly growing submerged plant, which grows on the bottom of a lake with its roots attached to the sediment. Water depth and turbidity, which affect the availability of in situ light, seem to be the main drivers for the shift from the regime dominated by Potamogeton pectinatus and Potamogeton perfoliatus to the Chara spp. dominated regime. However, this is speculative because it is not clear whether luxuriant air plant growth, high turbulence, nutrients and grazing by herbivorous birds had an impact on the shift, too. 

Type of regime shift

Ecosystem type

  • Freshwater lakes & rivers

Land uses

  • Large-scale commercial crop cultivation
  • Intensive livestock production (eg feedlots, dairies)

Spatial scale of the case study

  • Local/landscape (e.g. lake, catchment, community)

Continent or Ocean

  • Europe

Region

  • Province Flevoland, Province Gelderland

Countries

  • Netherlands

Locate with Google Map

Alternate regimes

Cichlid dominated regime (1950s – 1980s)

The regime was characterized by a lake of high biodiversity dominated by different species of native haplochromine cichlids (Balirwa et al. 2003; UNEP 2010). Cichlids span over many different trophic levels and represent nearly all different functional groups in Lake Victoria (UNEP 2010). In this regime the lake was less eutrophic compared to the current regime and thus less turbid. Nile perch was already introduced to the lake but populations remained low.

In the lake basin there were many local communities living on subsistence farming and small-scale fishing (Swallow 2009). The native fish species provided food for the local communities and the fishing for native cichlids was non-commercial but still population growth in the region put a large pressure on the native fish stocks (Seehausen et al. 1997).

Nile perch-dominated regime (From 1980s)

In this current regime the system has much reduced biodiverse lake with high abundance of only three species, the dominant Nile perch Lates niloticus, Nile tilapia Oreochromis niloticus (Balirwa et al. 2003), and a native cyprinid Rastrineobola argentea (UNEP 2010). The cyprinid is competing for the same resources as some cichlids (Matsuishi et al. 2006) and thus became very abundant once the cichlids disappeared. This low diversity makes the system vulnerable to disturbances (Balirwa et al. 2003; UNEP 2010). Eutrophication is an ever increasing problem resulting in algae blooms, turbidity, and hypoxia (Balirwa et al. 2003), all of which are undesirable conditions for the native species.

The fishing of Nile perch created a global market for fish export. The fishing industries involved many from the local communities and there was an increase in income for those in the Nile perch business. However, the changes brought many social problems emerging from unequal distribution of the increased income (Geheb et al. 2008). 

Drivers and causes of the regime shift

The apparent extinction of several hundreds of cichlid species was caused by Nile perch predation (Goudswaard et al. 2008). However, this event was preceded by drivers that weakened the cichlid population and opened up the field for the Nile perch. One of the main drivers was the increased pressure on the Lake Victoria cichlids by fisheries. At the beginning of the 1980s, cichlids accounted for more than 90 percent of the catch (Balirwa 2007). The other main driver was the increase in nutrient input from the Lake Victoria surroundings, leading to instances of algae blooms and hypoxia. The deoxygenation created an environment which was not suitable for the cichlids, many of which inhabited lower water columns where the oxygen deficiency was most acute (Hecky et al. 1994). The increase in nutrient inputs also caused turbidity which contributed to the reduction of reproductive capacity among cichlids (Seehausen et al. 1997).

The underlying driver of both of these developments is the human population growth around the lake, accelerating fishery activities and off-shore developments such as deforestation and expansion of agriculture which fed the lake with nutrient run-offs (Ibid.). Another cause of the demise of the cichlids was the heavy rainfall events during the 1960s. This external shock destroyed littoral vegetation around the lake which had served as important spawning and nursery grounds for native species. This enabled another species, the Nile tilapia, to conquer some of these areas and outcompete cichlids (Kaufman 1992). At this time the system was resilient enough to avert a shift but these events were precursors to later developments. 

How the regime shift worked

Under the cichlid dominated regime, Lake Victoria was an ecosystem with high species diversity. By eating basically everything in the lake these cichlids performed tight internal recycling (Kaufman 1992) and the pelagic planktivorous and detritivorous cichlids occupied a significant role in protecting the system against the excess production of phytoplankton (Goldschmidt et al. 1993). This allowed allowed resilience against increased nutrient input. The dominance of the cichlids also suppressed other species, including the Nile perch. The cichlids fed upon Nile perch larvae and competed with Nile perch juveniles for space and food (Goudswaard et al. 2008). These dynamics might explain why it took the Nile perch decades to accomplish its virtual takeover of the lake; as long as the cichlids were abundant, the Nile perch reproduction was suppressed (Ibid.).

However, due to the combined threats of Nile perch predation, overfishing, and the increasing nutrient inputs, this changed. First, the overfishing severely reduced the cichlid population in certain areas. Once the cichlid stock was reduced the Nile perch juveniles were able to colonize the areas. From there on, the Nile perch population could grow, invade neighboring areas, reduce the cichlids, and open up new areas for the recruitment of Nile perch juveniles (Ibid.). In this new regime, the Nile perch was the dominator and cichlids then dominated. When the cichlids started to disappear, this situation was opportunistically exploited by other species, including native shrimps. In the absence of the cichlids the shrimp population grew massively and became the most important source of food for the Nile perch (Kaufman 1992, Goldschmidt et al. 1993).

The reduction of cichlids, in combination with the spike in nutrient input, in turn had detrimental effects on the nutrient recycling, resulting in hypoxia. Those cichlids which had inhabited the lower water columns, and had therefore avoided Nile perch, were forced to migrate to shallow waters to escape the hypoxic waters. In these shallow waters they became the target of Nile perch predation (Hecky et al. 1994). 

Impacts on ecosystem services and human well-being

Both before and after the regime shift, Lake Victoria has been providing important provisioning ecosystem services, primarily fisheries. Before the shift, these fisheries were run by small-scale fishermen and operators; women were largely involved in the business (Abila & Jansen 1997), and the fish was for local consumption. However, the Nile perch boom diminished the variety of native fish, and turned this food source into economically more valuable forms of fish meat (Geheb et al. 2008). Foreign investment brought processing plants to the lake's shores (Kaufman 1992), boosted fish export, and eventually turned the artisanal fishery into a large-scale international enterprise. Another provisioning ecosystem service, namely the provision of freshwater suffered from decreased water quality through the cichlids' disappearance (Kaufman 1992).

Cultural ecosystem services were gained in terms of (fishing) tourism but presumably lost in terms of ecosystem/biodiversity knowledge, and aesthetic values. Since the regime shift, the majority of local community members have been carrying out economic activities linked to the Nile Perch fishery. The livelihood for many has improved (Abila & Jansen 1997). However, income from the fishing industry has been unequally distributed (Geheb et al. 2008). Due to social gender inequalities mainly men have been drawing profits from the fisheries boom while women and children have often been victims of malnutrition which is high along the lake's shores (ibid.). Many women have been forced into prostitution which in turn has increased the number of HIV/Aids infections after the Nile perch boom (Appleton 2000). 

Management options

The Nile perch was introduced in Lake Victoria to improve the commercial fishing values (Balirwa et al. 2003). The social effects from this have had huge and diverse impacts on the local communities around the lake resulting in, on one side, a billion dollar export industry, and on the other side, malnutrition, unequally divided income, and increased spread of HIV/Aids (Béné & Merten 2007, Appleton 2000). Nothing was done to prevent the shift from the cichlid dominated regime to the Nile perch dominated regime in the 1980s. Currently there are many different projects that work across the Lake Victoria Basin. The Lake Victoria Basin Commission (LVBC) is an institution of the East African Community which coordinates the policy and management agenda for the region (LVBC 2011). The program works for local community participation, poverty reduction and environmental concerns. Health issues, especially HIV/Aids (LVFO 2011) and human well-being are the most important parts of many different projects working in the lake surroundings. Some projects in the Kenyan part of the Lake Victoria basin mentioned by Swallow 2009 are the TransVic project byWorld Agroforestry Center, the Western Kenya Integrated Ecosystem Management Project and Vi Agroforestry (Swallow 2003 and 2009). These are all focusing on land degradation and agroforestry as land use management methods which both reduce the nutrient input to improve the lake conditions and work for poverty reduction (ibid.). 

A return to a regime with low abundance of Nile perch is not the focus of management and action plans (Schindler et al. 1998, Kitchell 1997) since the economic value of the Nile perch is so important. The ecological focus is rather on restoration of biodiversity, the lake ecosystem services, and the sustainability of the fisheries in the lake. A sustainable fishing of Nile perch can be reached by the control of fishing practices(Seehausen et al. 1997a). A study by Schindler et al. in 1998 show that by using a minimum mesh size of 5-inches the Nile perch cannibalism and the predation of native species can be reduced by 44% at the same time as the catches of Nile perch is only reduced by 10%. The re-emergence of native cichlids is an important step in the lake management to restore biodiversity in the lake system. By continuing the fishing of Nile perch the species is held at a controlled level giving the cichlids an opportunity to return to the system. For this it is also of great importance to improve the lake conditions by reducing the leakage of nutrients into the lake e.g. through investments in sewage treatment and restoration of wetlands in the basin area (Balirwa et al. 2003).

 

 

Alternate regimes

Cichlid dominated regime (1950s – 1980s)

The regime was characterized by a lake of high biodiversity dominated by different species of native haplochromine cichlids (Balirwa et al. 2003; UNEP 2010). Cichlids span over many different trophic levels and represent nearly all different functional groups in Lake Victoria (UNEP 2010). In this regime the lake was less eutrophic compared to the current regime and thus less turbid. Nile perch was already introduced to the lake but populations remained low.

In the lake basin there were many local communities living on subsistence farming and small-scale fishing (Swallow 2009). The native fish species provided food for the local communities and the fishing for native cichlids was non-commercial but still population growth in the region put a large pressure on the native fish stocks (Seehausen et al. 1997).

Nile perch-dominated regime (From 1980s)

In this current regime the system has much reduced biodiverse lake with high abundance of only three species, the dominant Nile perch Lates niloticus, Nile tilapia Oreochromis niloticus (Balirwa et al. 2003), and a native cyprinid Rastrineobola argentea (UNEP 2010). The cyprinid is competing for the same resources as some cichlids (Matsuishi et al. 2006) and thus became very abundant once the cichlids disappeared. This low diversity makes the system vulnerable to disturbances (Balirwa et al. 2003; UNEP 2010). Eutrophication is an ever increasing problem resulting in algae blooms, turbidity, and hypoxia (Balirwa et al. 2003), all of which are undesirable conditions for the native species.

The fishing of Nile perch created a global market for fish export. The fishing industries involved many from the local communities and there was an increase in income for those in the Nile perch business. However, the changes brought many social problems emerging from unequal distribution of the increased income (Geheb et al. 2008). 

Drivers and causes of the regime shift

The apparent extinction of several hundreds of cichlid species was caused by Nile perch predation (Goudswaard et al. 2008). However, this event was preceded by drivers that weakened the cichlid population and opened up the field for the Nile perch. One of the main drivers was the increased pressure on the Lake Victoria cichlids by fisheries. At the beginning of the 1980s, cichlids accounted for more than 90 percent of the catch (Balirwa 2007). The other main driver was the increase in nutrient input from the Lake Victoria surroundings, leading to instances of algae blooms and hypoxia. The deoxygenation created an environment which was not suitable for the cichlids, many of which inhabited lower water columns where the oxygen deficiency was most acute (Hecky et al. 1994). The increase in nutrient inputs also caused turbidity which contributed to the reduction of reproductive capacity among cichlids (Seehausen et al. 1997).

The underlying driver of both of these developments is the human population growth around the lake, accelerating fishery activities and off-shore developments such as deforestation and expansion of agriculture which fed the lake with nutrient run-offs (Ibid.). Another cause of the demise of the cichlids was the heavy rainfall events during the 1960s. This external shock destroyed littoral vegetation around the lake which had served as important spawning and nursery grounds for native species. This enabled another species, the Nile tilapia, to conquer some of these areas and outcompete cichlids (Kaufman 1992). At this time the system was resilient enough to avert a shift but these events were precursors to later developments. 

How the regime shift worked

Under the cichlid dominated regime, Lake Victoria was an ecosystem with high species diversity. By eating basically everything in the lake these cichlids performed tight internal recycling (Kaufman 1992) and the pelagic planktivorous and detritivorous cichlids occupied a significant role in protecting the system against the excess production of phytoplankton (Goldschmidt et al. 1993). This allowed allowed resilience against increased nutrient input. The dominance of the cichlids also suppressed other species, including the Nile perch. The cichlids fed upon Nile perch larvae and competed with Nile perch juveniles for space and food (Goudswaard et al. 2008). These dynamics might explain why it took the Nile perch decades to accomplish its virtual takeover of the lake; as long as the cichlids were abundant, the Nile perch reproduction was suppressed (Ibid.).

However, due to the combined threats of Nile perch predation, overfishing, and the increasing nutrient inputs, this changed. First, the overfishing severely reduced the cichlid population in certain areas. Once the cichlid stock was reduced the Nile perch juveniles were able to colonize the areas. From there on, the Nile perch population could grow, invade neighboring areas, reduce the cichlids, and open up new areas for the recruitment of Nile perch juveniles (Ibid.). In this new regime, the Nile perch was the dominator and cichlids then dominated. When the cichlids started to disappear, this situation was opportunistically exploited by other species, including native shrimps. In the absence of the cichlids the shrimp population grew massively and became the most important source of food for the Nile perch (Kaufman 1992, Goldschmidt et al. 1993).

The reduction of cichlids, in combination with the spike in nutrient input, in turn had detrimental effects on the nutrient recycling, resulting in hypoxia. Those cichlids which had inhabited the lower water columns, and had therefore avoided Nile perch, were forced to migrate to shallow waters to escape the hypoxic waters. In these shallow waters they became the target of Nile perch predation (Hecky et al. 1994). 

Impacts on ecosystem services and human well-being

Both before and after the regime shift, Lake Victoria has been providing important provisioning ecosystem services, primarily fisheries. Before the shift, these fisheries were run by small-scale fishermen and operators; women were largely involved in the business (Abila & Jansen 1997), and the fish was for local consumption. However, the Nile perch boom diminished the variety of native fish, and turned this food source into economically more valuable forms of fish meat (Geheb et al. 2008). Foreign investment brought processing plants to the lake's shores (Kaufman 1992), boosted fish export, and eventually turned the artisanal fishery into a large-scale international enterprise. Another provisioning ecosystem service, namely the provision of freshwater suffered from decreased water quality through the cichlids' disappearance (Kaufman 1992).

Cultural ecosystem services were gained in terms of (fishing) tourism but presumably lost in terms of ecosystem/biodiversity knowledge, and aesthetic values. Since the regime shift, the majority of local community members have been carrying out economic activities linked to the Nile Perch fishery. The livelihood for many has improved (Abila & Jansen 1997). However, income from the fishing industry has been unequally distributed (Geheb et al. 2008). Due to social gender inequalities mainly men have been drawing profits from the fisheries boom while women and children have often been victims of malnutrition which is high along the lake's shores (ibid.). Many women have been forced into prostitution which in turn has increased the number of HIV/Aids infections after the Nile perch boom (Appleton 2000). 

Management options

The Nile perch was introduced in Lake Victoria to improve the commercial fishing values (Balirwa et al. 2003). The social effects from this have had huge and diverse impacts on the local communities around the lake resulting in, on one side, a billion dollar export industry, and on the other side, malnutrition, unequally divided income, and increased spread of HIV/Aids (Béné & Merten 2007, Appleton 2000). Nothing was done to prevent the shift from the cichlid dominated regime to the Nile perch dominated regime in the 1980s. Currently there are many different projects that work across the Lake Victoria Basin. The Lake Victoria Basin Commission (LVBC) is an institution of the East African Community which coordinates the policy and management agenda for the region (LVBC 2011). The program works for local community participation, poverty reduction and environmental concerns. Health issues, especially HIV/Aids (LVFO 2011) and human well-being are the most important parts of many different projects working in the lake surroundings. Some projects in the Kenyan part of the Lake Victoria basin mentioned by Swallow 2009 are the TransVic project byWorld Agroforestry Center, the Western Kenya Integrated Ecosystem Management Project and Vi Agroforestry (Swallow 2003 and 2009). These are all focusing on land degradation and agroforestry as land use management methods which both reduce the nutrient input to improve the lake conditions and work for poverty reduction (ibid.). 

A return to a regime with low abundance of Nile perch is not the focus of management and action plans (Schindler et al. 1998, Kitchell 1997) since the economic value of the Nile perch is so important. The ecological focus is rather on restoration of biodiversity, the lake ecosystem services, and the sustainability of the fisheries in the lake. A sustainable fishing of Nile perch can be reached by the control of fishing practices(Seehausen et al. 1997a). A study by Schindler et al. in 1998 show that by using a minimum mesh size of 5-inches the Nile perch cannibalism and the predation of native species can be reduced by 44% at the same time as the catches of Nile perch is only reduced by 10%. The re-emergence of native cichlids is an important step in the lake management to restore biodiversity in the lake system. By continuing the fishing of Nile perch the species is held at a controlled level giving the cichlids an opportunity to return to the system. For this it is also of great importance to improve the lake conditions by reducing the leakage of nutrients into the lake e.g. through investments in sewage treatment and restoration of wetlands in the basin area (Balirwa et al. 2003).

 

 

Key References

  1. Coops H, Doef RW. 1996. Submerged vegetation development in two shallow, eutrophic lakes. Hydrobiologia 340, 115-120.
  2. Van den Berg MS, Coops H, Noordhuis R, Van Schie J, Simons J. 1997. Macroinvertebrate communities in relation to submerged vegetation in two Chara-dominated lakes. Hydrobiologia 342, 143-150.

Citation

Henning Nolzen, Reinette (Oonsie) Biggs, Garry Peterson. Lake Veluwemeer & Lake Wolderwijd, Netherlands. In: Regime Shifts Database, www.regimeshifts.org. Last revised 2012-03-17 19:19:37 GMT.
Thursday, 15 March 2012 15:49

Dutch ditches, Netherlands

Written by Reinette (Oonsie) Biggs

Dutch ditches, Netherlands

Main Contributors:

Henning Nolzen

Other Contributors:

Reinette (Oonsie) Biggs, Garry Peterson

Summary

In this case study, a dataset of vegetation censuses and water quality from 641 Dutch ditches were analyzed. Vegetation was non-selectively removed from such ditches once or twice a year to see which regime is dominant, a submerged or a floating plant dominated regime. The dataset was divided in a sparsely vegetated subset (total cover of all taxa 50 %) and a very densely vegetated subset (total cover > 80 %).  

 

For high vegetation densities the results of the case study showed that

- Cover by floating plants was negatively correlated to submerged plant abundance.

- Floating plants showed a positive correlation to nutrient levels of the water column.

- Submerged plants were negatively related to nutrient levels.  

 

For low vegetation densities the results showed that

- Correlations between growth forms and nutrient concentrations are less pronounced.

- Abundances of floating and submerged plants are positively correlated in a phase of regrowth after removal of vegetation.  

 

The key driver that is responsible for a shift to the floating plant dominated regime is a drastic harvest of floating plants. 

Type of regime shift

Ecosystem type

  • Freshwater lakes & rivers

Land uses

  • Large-scale commercial crop cultivation
  • Intensive livestock production (eg feedlots, dairies)

Spatial scale of the case study

  • Local/landscape (e.g. lake, catchment, community)

Continent or Ocean

  • Europe

Region

  • Province Flevoland, Province Gelderland

Countries

  • Netherlands

Locate with Google Map

Alternate regimes

Cichlid dominated regime (1950s – 1980s)

The regime was characterized by a lake of high biodiversity dominated by different species of native haplochromine cichlids (Balirwa et al. 2003; UNEP 2010). Cichlids span over many different trophic levels and represent nearly all different functional groups in Lake Victoria (UNEP 2010). In this regime the lake was less eutrophic compared to the current regime and thus less turbid. Nile perch was already introduced to the lake but populations remained low.

In the lake basin there were many local communities living on subsistence farming and small-scale fishing (Swallow 2009). The native fish species provided food for the local communities and the fishing for native cichlids was non-commercial but still population growth in the region put a large pressure on the native fish stocks (Seehausen et al. 1997).

Nile perch-dominated regime (From 1980s)

In this current regime the system has much reduced biodiverse lake with high abundance of only three species, the dominant Nile perch Lates niloticus, Nile tilapia Oreochromis niloticus (Balirwa et al. 2003), and a native cyprinid Rastrineobola argentea (UNEP 2010). The cyprinid is competing for the same resources as some cichlids (Matsuishi et al. 2006) and thus became very abundant once the cichlids disappeared. This low diversity makes the system vulnerable to disturbances (Balirwa et al. 2003; UNEP 2010). Eutrophication is an ever increasing problem resulting in algae blooms, turbidity, and hypoxia (Balirwa et al. 2003), all of which are undesirable conditions for the native species.

The fishing of Nile perch created a global market for fish export. The fishing industries involved many from the local communities and there was an increase in income for those in the Nile perch business. However, the changes brought many social problems emerging from unequal distribution of the increased income (Geheb et al. 2008). 

Drivers and causes of the regime shift

The apparent extinction of several hundreds of cichlid species was caused by Nile perch predation (Goudswaard et al. 2008). However, this event was preceded by drivers that weakened the cichlid population and opened up the field for the Nile perch. One of the main drivers was the increased pressure on the Lake Victoria cichlids by fisheries. At the beginning of the 1980s, cichlids accounted for more than 90 percent of the catch (Balirwa 2007). The other main driver was the increase in nutrient input from the Lake Victoria surroundings, leading to instances of algae blooms and hypoxia. The deoxygenation created an environment which was not suitable for the cichlids, many of which inhabited lower water columns where the oxygen deficiency was most acute (Hecky et al. 1994). The increase in nutrient inputs also caused turbidity which contributed to the reduction of reproductive capacity among cichlids (Seehausen et al. 1997).

The underlying driver of both of these developments is the human population growth around the lake, accelerating fishery activities and off-shore developments such as deforestation and expansion of agriculture which fed the lake with nutrient run-offs (Ibid.). Another cause of the demise of the cichlids was the heavy rainfall events during the 1960s. This external shock destroyed littoral vegetation around the lake which had served as important spawning and nursery grounds for native species. This enabled another species, the Nile tilapia, to conquer some of these areas and outcompete cichlids (Kaufman 1992). At this time the system was resilient enough to avert a shift but these events were precursors to later developments. 

How the regime shift worked

Under the cichlid dominated regime, Lake Victoria was an ecosystem with high species diversity. By eating basically everything in the lake these cichlids performed tight internal recycling (Kaufman 1992) and the pelagic planktivorous and detritivorous cichlids occupied a significant role in protecting the system against the excess production of phytoplankton (Goldschmidt et al. 1993). This allowed allowed resilience against increased nutrient input. The dominance of the cichlids also suppressed other species, including the Nile perch. The cichlids fed upon Nile perch larvae and competed with Nile perch juveniles for space and food (Goudswaard et al. 2008). These dynamics might explain why it took the Nile perch decades to accomplish its virtual takeover of the lake; as long as the cichlids were abundant, the Nile perch reproduction was suppressed (Ibid.).

However, due to the combined threats of Nile perch predation, overfishing, and the increasing nutrient inputs, this changed. First, the overfishing severely reduced the cichlid population in certain areas. Once the cichlid stock was reduced the Nile perch juveniles were able to colonize the areas. From there on, the Nile perch population could grow, invade neighboring areas, reduce the cichlids, and open up new areas for the recruitment of Nile perch juveniles (Ibid.). In this new regime, the Nile perch was the dominator and cichlids then dominated. When the cichlids started to disappear, this situation was opportunistically exploited by other species, including native shrimps. In the absence of the cichlids the shrimp population grew massively and became the most important source of food for the Nile perch (Kaufman 1992, Goldschmidt et al. 1993).

The reduction of cichlids, in combination with the spike in nutrient input, in turn had detrimental effects on the nutrient recycling, resulting in hypoxia. Those cichlids which had inhabited the lower water columns, and had therefore avoided Nile perch, were forced to migrate to shallow waters to escape the hypoxic waters. In these shallow waters they became the target of Nile perch predation (Hecky et al. 1994). 

Impacts on ecosystem services and human well-being

Both before and after the regime shift, Lake Victoria has been providing important provisioning ecosystem services, primarily fisheries. Before the shift, these fisheries were run by small-scale fishermen and operators; women were largely involved in the business (Abila & Jansen 1997), and the fish was for local consumption. However, the Nile perch boom diminished the variety of native fish, and turned this food source into economically more valuable forms of fish meat (Geheb et al. 2008). Foreign investment brought processing plants to the lake's shores (Kaufman 1992), boosted fish export, and eventually turned the artisanal fishery into a large-scale international enterprise. Another provisioning ecosystem service, namely the provision of freshwater suffered from decreased water quality through the cichlids' disappearance (Kaufman 1992).

Cultural ecosystem services were gained in terms of (fishing) tourism but presumably lost in terms of ecosystem/biodiversity knowledge, and aesthetic values. Since the regime shift, the majority of local community members have been carrying out economic activities linked to the Nile Perch fishery. The livelihood for many has improved (Abila & Jansen 1997). However, income from the fishing industry has been unequally distributed (Geheb et al. 2008). Due to social gender inequalities mainly men have been drawing profits from the fisheries boom while women and children have often been victims of malnutrition which is high along the lake's shores (ibid.). Many women have been forced into prostitution which in turn has increased the number of HIV/Aids infections after the Nile perch boom (Appleton 2000). 

Management options

The Nile perch was introduced in Lake Victoria to improve the commercial fishing values (Balirwa et al. 2003). The social effects from this have had huge and diverse impacts on the local communities around the lake resulting in, on one side, a billion dollar export industry, and on the other side, malnutrition, unequally divided income, and increased spread of HIV/Aids (Béné & Merten 2007, Appleton 2000). Nothing was done to prevent the shift from the cichlid dominated regime to the Nile perch dominated regime in the 1980s. Currently there are many different projects that work across the Lake Victoria Basin. The Lake Victoria Basin Commission (LVBC) is an institution of the East African Community which coordinates the policy and management agenda for the region (LVBC 2011). The program works for local community participation, poverty reduction and environmental concerns. Health issues, especially HIV/Aids (LVFO 2011) and human well-being are the most important parts of many different projects working in the lake surroundings. Some projects in the Kenyan part of the Lake Victoria basin mentioned by Swallow 2009 are the TransVic project byWorld Agroforestry Center, the Western Kenya Integrated Ecosystem Management Project and Vi Agroforestry (Swallow 2003 and 2009). These are all focusing on land degradation and agroforestry as land use management methods which both reduce the nutrient input to improve the lake conditions and work for poverty reduction (ibid.). 

A return to a regime with low abundance of Nile perch is not the focus of management and action plans (Schindler et al. 1998, Kitchell 1997) since the economic value of the Nile perch is so important. The ecological focus is rather on restoration of biodiversity, the lake ecosystem services, and the sustainability of the fisheries in the lake. A sustainable fishing of Nile perch can be reached by the control of fishing practices(Seehausen et al. 1997a). A study by Schindler et al. in 1998 show that by using a minimum mesh size of 5-inches the Nile perch cannibalism and the predation of native species can be reduced by 44% at the same time as the catches of Nile perch is only reduced by 10%. The re-emergence of native cichlids is an important step in the lake management to restore biodiversity in the lake system. By continuing the fishing of Nile perch the species is held at a controlled level giving the cichlids an opportunity to return to the system. For this it is also of great importance to improve the lake conditions by reducing the leakage of nutrients into the lake e.g. through investments in sewage treatment and restoration of wetlands in the basin area (Balirwa et al. 2003).

 

 

Alternate regimes

Cichlid dominated regime (1950s – 1980s)

The regime was characterized by a lake of high biodiversity dominated by different species of native haplochromine cichlids (Balirwa et al. 2003; UNEP 2010). Cichlids span over many different trophic levels and represent nearly all different functional groups in Lake Victoria (UNEP 2010). In this regime the lake was less eutrophic compared to the current regime and thus less turbid. Nile perch was already introduced to the lake but populations remained low.

In the lake basin there were many local communities living on subsistence farming and small-scale fishing (Swallow 2009). The native fish species provided food for the local communities and the fishing for native cichlids was non-commercial but still population growth in the region put a large pressure on the native fish stocks (Seehausen et al. 1997).

Nile perch-dominated regime (From 1980s)

In this current regime the system has much reduced biodiverse lake with high abundance of only three species, the dominant Nile perch Lates niloticus, Nile tilapia Oreochromis niloticus (Balirwa et al. 2003), and a native cyprinid Rastrineobola argentea (UNEP 2010). The cyprinid is competing for the same resources as some cichlids (Matsuishi et al. 2006) and thus became very abundant once the cichlids disappeared. This low diversity makes the system vulnerable to disturbances (Balirwa et al. 2003; UNEP 2010). Eutrophication is an ever increasing problem resulting in algae blooms, turbidity, and hypoxia (Balirwa et al. 2003), all of which are undesirable conditions for the native species.

The fishing of Nile perch created a global market for fish export. The fishing industries involved many from the local communities and there was an increase in income for those in the Nile perch business. However, the changes brought many social problems emerging from unequal distribution of the increased income (Geheb et al. 2008). 

Drivers and causes of the regime shift

The apparent extinction of several hundreds of cichlid species was caused by Nile perch predation (Goudswaard et al. 2008). However, this event was preceded by drivers that weakened the cichlid population and opened up the field for the Nile perch. One of the main drivers was the increased pressure on the Lake Victoria cichlids by fisheries. At the beginning of the 1980s, cichlids accounted for more than 90 percent of the catch (Balirwa 2007). The other main driver was the increase in nutrient input from the Lake Victoria surroundings, leading to instances of algae blooms and hypoxia. The deoxygenation created an environment which was not suitable for the cichlids, many of which inhabited lower water columns where the oxygen deficiency was most acute (Hecky et al. 1994). The increase in nutrient inputs also caused turbidity which contributed to the reduction of reproductive capacity among cichlids (Seehausen et al. 1997).

The underlying driver of both of these developments is the human population growth around the lake, accelerating fishery activities and off-shore developments such as deforestation and expansion of agriculture which fed the lake with nutrient run-offs (Ibid.). Another cause of the demise of the cichlids was the heavy rainfall events during the 1960s. This external shock destroyed littoral vegetation around the lake which had served as important spawning and nursery grounds for native species. This enabled another species, the Nile tilapia, to conquer some of these areas and outcompete cichlids (Kaufman 1992). At this time the system was resilient enough to avert a shift but these events were precursors to later developments. 

How the regime shift worked

Under the cichlid dominated regime, Lake Victoria was an ecosystem with high species diversity. By eating basically everything in the lake these cichlids performed tight internal recycling (Kaufman 1992) and the pelagic planktivorous and detritivorous cichlids occupied a significant role in protecting the system against the excess production of phytoplankton (Goldschmidt et al. 1993). This allowed allowed resilience against increased nutrient input. The dominance of the cichlids also suppressed other species, including the Nile perch. The cichlids fed upon Nile perch larvae and competed with Nile perch juveniles for space and food (Goudswaard et al. 2008). These dynamics might explain why it took the Nile perch decades to accomplish its virtual takeover of the lake; as long as the cichlids were abundant, the Nile perch reproduction was suppressed (Ibid.).

However, due to the combined threats of Nile perch predation, overfishing, and the increasing nutrient inputs, this changed. First, the overfishing severely reduced the cichlid population in certain areas. Once the cichlid stock was reduced the Nile perch juveniles were able to colonize the areas. From there on, the Nile perch population could grow, invade neighboring areas, reduce the cichlids, and open up new areas for the recruitment of Nile perch juveniles (Ibid.). In this new regime, the Nile perch was the dominator and cichlids then dominated. When the cichlids started to disappear, this situation was opportunistically exploited by other species, including native shrimps. In the absence of the cichlids the shrimp population grew massively and became the most important source of food for the Nile perch (Kaufman 1992, Goldschmidt et al. 1993).

The reduction of cichlids, in combination with the spike in nutrient input, in turn had detrimental effects on the nutrient recycling, resulting in hypoxia. Those cichlids which had inhabited the lower water columns, and had therefore avoided Nile perch, were forced to migrate to shallow waters to escape the hypoxic waters. In these shallow waters they became the target of Nile perch predation (Hecky et al. 1994). 

Impacts on ecosystem services and human well-being

Both before and after the regime shift, Lake Victoria has been providing important provisioning ecosystem services, primarily fisheries. Before the shift, these fisheries were run by small-scale fishermen and operators; women were largely involved in the business (Abila & Jansen 1997), and the fish was for local consumption. However, the Nile perch boom diminished the variety of native fish, and turned this food source into economically more valuable forms of fish meat (Geheb et al. 2008). Foreign investment brought processing plants to the lake's shores (Kaufman 1992), boosted fish export, and eventually turned the artisanal fishery into a large-scale international enterprise. Another provisioning ecosystem service, namely the provision of freshwater suffered from decreased water quality through the cichlids' disappearance (Kaufman 1992).

Cultural ecosystem services were gained in terms of (fishing) tourism but presumably lost in terms of ecosystem/biodiversity knowledge, and aesthetic values. Since the regime shift, the majority of local community members have been carrying out economic activities linked to the Nile Perch fishery. The livelihood for many has improved (Abila & Jansen 1997). However, income from the fishing industry has been unequally distributed (Geheb et al. 2008). Due to social gender inequalities mainly men have been drawing profits from the fisheries boom while women and children have often been victims of malnutrition which is high along the lake's shores (ibid.). Many women have been forced into prostitution which in turn has increased the number of HIV/Aids infections after the Nile perch boom (Appleton 2000). 

Management options

The Nile perch was introduced in Lake Victoria to improve the commercial fishing values (Balirwa et al. 2003). The social effects from this have had huge and diverse impacts on the local communities around the lake resulting in, on one side, a billion dollar export industry, and on the other side, malnutrition, unequally divided income, and increased spread of HIV/Aids (Béné & Merten 2007, Appleton 2000). Nothing was done to prevent the shift from the cichlid dominated regime to the Nile perch dominated regime in the 1980s. Currently there are many different projects that work across the Lake Victoria Basin. The Lake Victoria Basin Commission (LVBC) is an institution of the East African Community which coordinates the policy and management agenda for the region (LVBC 2011). The program works for local community participation, poverty reduction and environmental concerns. Health issues, especially HIV/Aids (LVFO 2011) and human well-being are the most important parts of many different projects working in the lake surroundings. Some projects in the Kenyan part of the Lake Victoria basin mentioned by Swallow 2009 are the TransVic project byWorld Agroforestry Center, the Western Kenya Integrated Ecosystem Management Project and Vi Agroforestry (Swallow 2003 and 2009). These are all focusing on land degradation and agroforestry as land use management methods which both reduce the nutrient input to improve the lake conditions and work for poverty reduction (ibid.). 

A return to a regime with low abundance of Nile perch is not the focus of management and action plans (Schindler et al. 1998, Kitchell 1997) since the economic value of the Nile perch is so important. The ecological focus is rather on restoration of biodiversity, the lake ecosystem services, and the sustainability of the fisheries in the lake. A sustainable fishing of Nile perch can be reached by the control of fishing practices(Seehausen et al. 1997a). A study by Schindler et al. in 1998 show that by using a minimum mesh size of 5-inches the Nile perch cannibalism and the predation of native species can be reduced by 44% at the same time as the catches of Nile perch is only reduced by 10%. The re-emergence of native cichlids is an important step in the lake management to restore biodiversity in the lake system. By continuing the fishing of Nile perch the species is held at a controlled level giving the cichlids an opportunity to return to the system. For this it is also of great importance to improve the lake conditions by reducing the leakage of nutrients into the lake e.g. through investments in sewage treatment and restoration of wetlands in the basin area (Balirwa et al. 2003).

 

 

Key References

  1. Scheffer M, Szabó S, Gragnani A, van Nes EH, Rinaldi S, Kautsky N, Norberg J, Roijackers RMM, Franken RJM. 2003. Floating plant dominance as a stable state. PNAS 100, Issue 7, 4040-4045.

Citation

Henning Nolzen, Reinette (Oonsie) Biggs, Garry Peterson. Dutch ditches, Netherlands. In: Regime Shifts Database, www.regimeshifts.org. Last revised 2012-03-17 19:14:45 GMT.