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Case Studies (330)

Thursday, 12 May 2011 12:35

Baltic Sea - pelagic food web

Written by Johanna

Baltic Sea - pelagic food web

Main Contributors:

Henrik Österblom, Johanna Yletyinen

Other Contributors:

Jonas Hentati-Sundberg, Thorsten Blenckner

Summary

The Baltic Sea is a semi-enclosed, brackish sea located in Northern Europe. The regime shift described for the Central Baltic Sea involves a drastic change from a cod- to a sprat-dominated ecosystem in a marine food web. Through the biomass decrease of a high trophic level, a commercially high valued and favored table fish was replaced by a low trophic level and low commercial value fish. The prerequisite for the change in the system was most probably loss of resilience, which was caused by poor cod recruitment conditions and too high fishing pressure. Anthropogenic eutrophication and infrequent inflows of saline water from the North Sea contributed to the changed deep water conditions in the Central Baltic, resulting in anoxia and low salinity lowering the cod reproduction rates. Since cod (Gadus morhua) is the main predator of sprat (Sprattus sprattus), the cod decrease caused a trophic cascade as the sprat stock dramatically increased. 

Type of regime shift

  • Unknown

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

  • Europe

Region

  • Northern Europe

Countries

  • Lithuania
  • Poland
  • Russia
  • Sweden
  • Denmark
  • Estonia
  • Finland
  • Germany
  • Latvia

Locate with Google Map

Drivers

Key direct drivers

  • Harvest and resource consumption
  • External inputs (eg fertilizers)
  • Species introduction or removal

Impacts

Ecosystem type

  • Marine & coastal

Key Ecosystem Processes

  • Nutrient cycling
  • Water cycling

Biodiversity

  • Biodiversity

Provisioning services

  • Fisheries

Regulating services

  • Water purification

Cultural services

  • Recreation
  • Aesthetic values

Human Well-being

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

Key Attributes

Spatial scale of RS

  • Sub-continental/regional

Time scale of RS

  • Years
  • Decades

Reversibility

  • Unknown

Evidence

  • Models
  • Contemporary observations
  • Experiments

Confidence: Existence of RS

  • Contested – Reasonable evidence both for and against the existence of RS

Confidence: Mechanism underlying RS

  • Contested – Multiple proposed mechanisms, reasonable evidence both for and against different mechanisms

Alternate regimes

The cod-dominated regime

The cod-dominated regime was characterized by abundant cod stocks, not only in the southern part of the Baltic Sea, but also further north and closer to shore. Cod predation regulated the number of sprat and herring. Pseudocalanus spp. dominated the zooplankton community. This regime was observed primarily during the early- to mid-1980s. 

Sprat-dominated regime

The sprat-dominated regime came into effect in 1989. A lower cod stock, an increased number of sprat and favorable conditions for sprat recruitment characterize the regime. In zooplankton community, Acartia spp. and Temora longicornis are more abundant than Psedocalanus spp. It is suggested that sprat's high predation on zooplankton lead to algal growth and declining oxygen content in deep waters. The high fishing pressure on cod is preventing the recovery of the stock and allowing the sprat to control the zooplankton. 

Drivers and causes of the regime shift

The key drivers for the Central Baltic cod-dominated regime to shift to a sprat-dominated regime are suggested to be poor cod recruitment conditions and too high fishing pressure caused by eutrophication, altered deep water conditions, infrequent inflows of North Sea saline waters and international fishing policies.

Climate functions as an indirect driver through changes in the physical environment and altered food supply for early stages. Decreased salinity, increased temperature and high sprat-predation pressure might have caused the regime subshift from Pseudocalanus spp. to Acartia spp. and Temora longicornis. Low salinity and oxygen conditions decrease the amount of the main prey of cod larvae. Higher temperatures support sprat recruitment by improving egg survival and food supply as Acartia spp. and Temora longicornis increase. 

How the regime shift worked

Cod is the main predator of sprat. It has been suggested that the large cod stock was able to control the sprat stock in the cod-dominated regime. Anthropogenic eutrophication and infrequent inflows of saline water from the North Sea contributed to increased anoxia and lowered salinity in the Central Baltic. Due to low salinity and oxygen content in the spawning areas, cod reproduction rates have remained low since the early 1980s. Deep water anoxia is a chronic stress for the survival of the cod eggs. Baltic cod needs salinity for the eggs to float in the water. If the required salinity is in anoxic conditions, eggs die.

Anoxia is one of the effects of the Baltic Sea eutrophication, but it can be temporarily reduced by inflows of North Sea saline waters, which replenish the deep-water layers of the Baltic Sea with saline and well-oxygenated water. Major Baltic Inflows decreased frequently in the early 1980s and there was a stagnation period until the early 1990s. Although the cod stock decreased due to cod recruitment decline caused by degraded environmental conditions, the fishing effort remained high. Unfavorable cod recruitment conditions and high fishing pressure caused a remarkable drop in cod biomass. As the Central Baltic Sea is characterized by simple food web with low species diversity, cod decrease allowed its' prey sprat to increase. Cod fishing further reduced the stock, making cod even more sensitive to adverse environmental conditions. International fishing quotas have been set to limit the cod fishing but they have not always been followed. The quotas have consistently been greater than the scientific recommendations.

Studies suggest that the large increase of the sprat stock has changed the system from mainly bottom-up to top-down trophic control. A trophic cascade occurred as the sprat stock dramatically increased. High sprat abundance changed the quantity and quality of zooplankton, which feeds on phytoplankton. A sub-shift in zooplankton species can be observed to have happened until the end of the 1980s: a shift in dominance occurred from Pseudocalanus spp., the main food supply for cod larvae, to the main food supply of sprat larvae and adults, Acartia spp. and Temora longicornis. Salinity, temperature, predation of sprat, herring and mysids and climate in general regulate the zooplankton species as they all have their specific abiotic preferences. Through trophic cascades large sprat stock also lead to higher phytoplankton biomass and algal blooms during summer. Algae growth promotes further anoxia. A sprat-dominated food web has been suggested to stabilize the cod stock by sprat predating on cod eggs and larvae, and through sprat competing with young cod for zooplankton resources. Changed abundance of sprat may have even been reflected to the top levels of the Baltic food web: the condition of Common Murre (Uria aalge) chicks seem to increase and decrease in relation to sprat stock. This way human exploitation combined to natural changes caused variations in several trophic levels, which altered the ecosystem functioning as the interaction between species changed.

 

Impacts on ecosystem services and human well-being

The main ecosystem services associated with the cod-dominated regime were commercially viable, high value cod stocks, recreational value of large cod stocks and a sustainable small-scale fishing sector favoring regional development. The regime was possibly related to high water quality stimulating tourism development. Cod provide the Baltic Sea region with provisioning services: Cod is commercially the most important species in the Baltic Sea for a large number of fishermen. In the sprat-dominated region, the economic value of the catch for human consumption decreases due to the relative composition of the fish species. Being a predator at the top of the food chain, cod provides the Baltic Sea with regulating ecosystem services: cod reduces sprat, which prey on zooplankton and early life stages of cod. The high summer levels of phytoplankton could partly be a result of the sprat predation-induced decrease in total zooplankton biomass. The decay of increased algae leads to oxygen deficit and thereby causes damage to the biodiversity. The regulating role of cod may also be reflected to the top levels of the Baltic food web, the sea birds. The sprat-dominated regime is dominated by low value fish used for reduction fisheries and international fish meal and fish oil markets. These large-scale fisheries are mainly based outside the Baltic Sea region, which makes the regime less advantageous for the local development. The sprat-dominated regime may be associated with cascading effects on water quality as the low biomass of summer zooplankton may increase the probability for cyanobacterial blooms.

Low cod biomass makes industrial fishing and businesses associated with recreational fishing less profitable. Increased occurrence of algal blooms makes the Baltic Sea less attractive for tourists and recreation. From the socioeconomic perspective, tourist industry is more important than fishing industry in for example Sweden. The Baltic Sea environment and its cultural fishing surroundings are important tourist attractions. The toxic blooms and low water quality are nuisance for coastal property owners, local enterprises, bathers and others seeking for creation on the coasts. 

Management options

The goal for managing the regime shift is to maintain the resilience of the Baltic Sea ecosystem by targeting eutrophication and recovery of the cod stock. The management actions to reduce nutrient pollution began in the 1970s, when Helsinki Commission (HELCOM) adopted several recommendations for all sectors (industry, agriculture, wastewater treatment). Since the 1980s, HELCOM has worked with the 50% reduction targets for nutrients and discharges. Several countries have recently agreed to substantially reduce fertilizer use in the region (Baltic Sea Action Plan). In 1990s, it became obvious that the important Baltic Sea fish stocks were in a poor state and the fisheries were not under satisfactory control. The International Baltic Sea Fishery Commission (IBSFC) reacted with several resolutions to reduce fishing mortality and improve selectivity for cod. The main initiatives were to improve control and enforcement to assure adherence to TACs, set TACs based on target fishing mortalities, introduce technical measures to improve selectivity, and seasonal closures of areas to protect the spawning stock. However, the overexploitation of cod resources continued: the scientific advice was disregarded when setting quotas and the quotas restricting exploitation were not enforced.

In 1999, a Long-Term Management Strategy for Cod Stocks in the Baltic Sea was made including e.g. efforts to maintain a minimum spawning-stock biomass. The Recovery Plan for Baltic Sea Cod was developed in 2001 requiring a.o. seasonal closures and ban on fishing on the cod spawning grounds. Still, the problems remained and in 2004 it was acknowledged that the state of the cod stock had not improved, requiring determined action based on scientific advice. The EU agreed a plan for the Baltic Sea cod in 2007. In 2009 and 2010, The European Council Regulation for the Baltic TAC involved reductions in the number of fishing days per year. The cod fisheries are regulated by a seasonal closure to protect spawning fish. A year-round area closure for all fisheries in specific parts of the Bornholm Deep, the Gotland Basin and the Gdansk Deep was introduced in 2005.

High-grading has been prohibited since 2010 in all Baltic fisheries. In 2003, the minimum landing size was raised from 35 cm to 38 cm to protect the juvenile cods, which have not had a chance to reproduce yet. Additionally, fishing nets with exit windows have been introduced. To combat illegal fishing EU Commission has made inspections on randomly selected vessels and concluded that illegal fishing is substantial and practiced by many Baltic Sea countries. 

Key References

  1. Alheit J, Möllman C, Dutz J, Kornilovs G, Loewe P, Mohrholz V, Wasmund N. 2005. Synchronous ecological regime shifts in the Central Baltic and the North Sea in the late 1980s. ICES Journal of Marine Sciences 62, 1205-1215.
  2. Aps R, Lassen H. 2010. Recovery of depleted Baltic Sea fish stocks: a review. ICES Journal of Marine Science 67, 1856–1860.
  3. Cardinale, M, Svedäng H. 2011. The beauty of simplicity in science: Baltic cod stock improves rapidly in a "cod hostile" ecosystem state. Marine Ecology Progress Series 425, 297-301.
  4. Casini M, Hjelm J, Molinero JC, Lovgren J et al. 2009. Trophic cascades promote threshold-like shifts in pelagic marine ecosystems. Proc Natl Acad Sci USA 106, 197–202.
  5. Casini M, Lovgren J, Hjelm J, Cardinale M, Molinero JC, Kornilovs G. 2008. Multi-level Trophic Cascades in a Heavily Expoited Open Marine Ecosystem. Proc R Soc B Biol Sci 275, 1793-1801
  6. Döring R, Egelkraut TM. 2007. Investing in natural capital as management strategy in fisheries: the case of the Baltic Sea cod fishery. Ecological Economics 64, 634-642.
  7. Hanninen J, Vourinen I, Hjelt P. 2000. Climatic factors in the Atlantic control of the oceanographic and ecological changes in the Baltic Sea. Limnology and Oceanography 45, 703-710.
  8. Heikinheimo, O. 2011. Interactions Between Cod, Herring and Sprat in The Changing Environment of The Baltic Sea: A Dynamic Model Analysis. Ecological Modeling 222, 1731 – 1742.
  9. Lindegren M, Diekmann R, Möllmann C. 2010. Regime Shifts, resilience and recovery of a cod stock. Marine Ecology Progress Series 402, 249 – 253.
  10. Möllmann C, Diekmann R, Müller-Karulis B, Kornilovs G, Plikshs M, Axe P. 2009. Reorganization of a large marine ecosystem due to atmospheric and anthropogenic pressure: a discontinuous regime shift in the Central Baltic Sea. Glob Change Biol 15, 1377–1393.
  11. Möllmann C, Müller-Karulis B, Kornilovs G, St. John MA. 2008. Effects of climate and overfishing on zooplankton dynamics and ecosystem structure: regime shifts, trophic cascade, and feedback loops in a simple ecosystem. ICES J Mar Sci 65, 302–310.
  12. Österblom H, Gårdmark A, Bergström L, Müller-Karulis B et al. 2010. Making the ecosystem approach operational: can regime shifts in ecological and governance systems facilitate the transition? Mar Pol 34, 1290–1299.
  13. Waldo S, Paulrud A, Jonsson A. 2010. A note on the economics of Swedish Baltic Sea fisheries. Marine Policy 34, 716-719.

Citation

Henrik Österblom, Johanna Yletyinen, Jonas Hentati-Sundberg, Thorsten Blenckner. Baltic Sea - pelagic food web. In: Regime Shifts Database, www.regimeshifts.org. Last revised 2012-03-19 12:58:03 GMT.
Thursday, 03 March 2011 12:39

Makanya catchment, Tanzania

Written by Johnny Musumbu

Makanya catchment, Tanzania

Main Contributors:

Johnny Musumbu Tshimpanga

Other Contributors:

Reinette (Oonsie) Biggs

Summary

The Makanya agro-ecological system as most of smallholder agro-ecosystems in dry-land environments has been conceptualised as a system that exhibits two alternative stability basins of attractions referred to respectively as productive and degraded regimes. The productive domains resulted from a distinctive kind of management both at field and landscape levels that involved extended fallow periods practices aimed at naturally regenerating soils fertility coupled with strong laws local together with rules and norms for natural resources management . Consequently, the system developed along a trajectory where plentiful and easily accessible of on- as well as off-farm provisioning ecosystem services was generated to support a relatively low population living in the system over time. Early 1980s, the agro-ecosystem underwent dramatic changes that happened concomitantly and pushed the system into the degraded regime. These changes encompass increasing dry-spell frequencies, rapid institutional changes, and population growth that triggered a spiral of mutually enforcing feedbacks, involving increased cropping intensity, cultivation of more marginal lands, yields declines, soil fertility decline and loss of provisioning ecosystem services generated by the catchment. That situation has inexorably set the system on a development path where food and other ecosystem services are not generated fast enough to support local population over time. As a result, local populations appear to be caught into a persistent poverty conditions referred to as poverty traps. There is, however, a window of opportunity which is conducive to sustainably dealing with these highly complex challenges. These include a mix of small water system technologies that bear high prospects for stabilising even increasing agro-ecological productivity, and efficient and enforceable institutional mechanisms that guarantee a successful resource base management.

Type of regime shift

  • Bio-productivity shift in dry-land agro-ecosystems

Ecosystem type

  • Drylands & deserts (below ~500mm rainfall/year)

Land uses

  • Small-scale subsistence crop cultivation

Spatial scale of the case study

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

Continent or Ocean

  • Africa

Region

  • Eastern Africa

Countries

  • Tanzania

Locate with Google Map

Alternate regimes

The cod-dominated regime

The cod-dominated regime was characterized by abundant cod stocks, not only in the southern part of the Baltic Sea, but also further north and closer to shore. Cod predation regulated the number of sprat and herring. Pseudocalanus spp. dominated the zooplankton community. This regime was observed primarily during the early- to mid-1980s. 

Sprat-dominated regime

The sprat-dominated regime came into effect in 1989. A lower cod stock, an increased number of sprat and favorable conditions for sprat recruitment characterize the regime. In zooplankton community, Acartia spp. and Temora longicornis are more abundant than Psedocalanus spp. It is suggested that sprat's high predation on zooplankton lead to algal growth and declining oxygen content in deep waters. The high fishing pressure on cod is preventing the recovery of the stock and allowing the sprat to control the zooplankton. 

Drivers and causes of the regime shift

The key drivers for the Central Baltic cod-dominated regime to shift to a sprat-dominated regime are suggested to be poor cod recruitment conditions and too high fishing pressure caused by eutrophication, altered deep water conditions, infrequent inflows of North Sea saline waters and international fishing policies.

Climate functions as an indirect driver through changes in the physical environment and altered food supply for early stages. Decreased salinity, increased temperature and high sprat-predation pressure might have caused the regime subshift from Pseudocalanus spp. to Acartia spp. and Temora longicornis. Low salinity and oxygen conditions decrease the amount of the main prey of cod larvae. Higher temperatures support sprat recruitment by improving egg survival and food supply as Acartia spp. and Temora longicornis increase. 

How the regime shift worked

Cod is the main predator of sprat. It has been suggested that the large cod stock was able to control the sprat stock in the cod-dominated regime. Anthropogenic eutrophication and infrequent inflows of saline water from the North Sea contributed to increased anoxia and lowered salinity in the Central Baltic. Due to low salinity and oxygen content in the spawning areas, cod reproduction rates have remained low since the early 1980s. Deep water anoxia is a chronic stress for the survival of the cod eggs. Baltic cod needs salinity for the eggs to float in the water. If the required salinity is in anoxic conditions, eggs die.

Anoxia is one of the effects of the Baltic Sea eutrophication, but it can be temporarily reduced by inflows of North Sea saline waters, which replenish the deep-water layers of the Baltic Sea with saline and well-oxygenated water. Major Baltic Inflows decreased frequently in the early 1980s and there was a stagnation period until the early 1990s. Although the cod stock decreased due to cod recruitment decline caused by degraded environmental conditions, the fishing effort remained high. Unfavorable cod recruitment conditions and high fishing pressure caused a remarkable drop in cod biomass. As the Central Baltic Sea is characterized by simple food web with low species diversity, cod decrease allowed its' prey sprat to increase. Cod fishing further reduced the stock, making cod even more sensitive to adverse environmental conditions. International fishing quotas have been set to limit the cod fishing but they have not always been followed. The quotas have consistently been greater than the scientific recommendations.

Studies suggest that the large increase of the sprat stock has changed the system from mainly bottom-up to top-down trophic control. A trophic cascade occurred as the sprat stock dramatically increased. High sprat abundance changed the quantity and quality of zooplankton, which feeds on phytoplankton. A sub-shift in zooplankton species can be observed to have happened until the end of the 1980s: a shift in dominance occurred from Pseudocalanus spp., the main food supply for cod larvae, to the main food supply of sprat larvae and adults, Acartia spp. and Temora longicornis. Salinity, temperature, predation of sprat, herring and mysids and climate in general regulate the zooplankton species as they all have their specific abiotic preferences. Through trophic cascades large sprat stock also lead to higher phytoplankton biomass and algal blooms during summer. Algae growth promotes further anoxia. A sprat-dominated food web has been suggested to stabilize the cod stock by sprat predating on cod eggs and larvae, and through sprat competing with young cod for zooplankton resources. Changed abundance of sprat may have even been reflected to the top levels of the Baltic food web: the condition of Common Murre (Uria aalge) chicks seem to increase and decrease in relation to sprat stock. This way human exploitation combined to natural changes caused variations in several trophic levels, which altered the ecosystem functioning as the interaction between species changed.

 

Impacts on ecosystem services and human well-being

The main ecosystem services associated with the cod-dominated regime were commercially viable, high value cod stocks, recreational value of large cod stocks and a sustainable small-scale fishing sector favoring regional development. The regime was possibly related to high water quality stimulating tourism development. Cod provide the Baltic Sea region with provisioning services: Cod is commercially the most important species in the Baltic Sea for a large number of fishermen. In the sprat-dominated region, the economic value of the catch for human consumption decreases due to the relative composition of the fish species. Being a predator at the top of the food chain, cod provides the Baltic Sea with regulating ecosystem services: cod reduces sprat, which prey on zooplankton and early life stages of cod. The high summer levels of phytoplankton could partly be a result of the sprat predation-induced decrease in total zooplankton biomass. The decay of increased algae leads to oxygen deficit and thereby causes damage to the biodiversity. The regulating role of cod may also be reflected to the top levels of the Baltic food web, the sea birds. The sprat-dominated regime is dominated by low value fish used for reduction fisheries and international fish meal and fish oil markets. These large-scale fisheries are mainly based outside the Baltic Sea region, which makes the regime less advantageous for the local development. The sprat-dominated regime may be associated with cascading effects on water quality as the low biomass of summer zooplankton may increase the probability for cyanobacterial blooms.

Low cod biomass makes industrial fishing and businesses associated with recreational fishing less profitable. Increased occurrence of algal blooms makes the Baltic Sea less attractive for tourists and recreation. From the socioeconomic perspective, tourist industry is more important than fishing industry in for example Sweden. The Baltic Sea environment and its cultural fishing surroundings are important tourist attractions. The toxic blooms and low water quality are nuisance for coastal property owners, local enterprises, bathers and others seeking for creation on the coasts. 

Management options

The goal for managing the regime shift is to maintain the resilience of the Baltic Sea ecosystem by targeting eutrophication and recovery of the cod stock. The management actions to reduce nutrient pollution began in the 1970s, when Helsinki Commission (HELCOM) adopted several recommendations for all sectors (industry, agriculture, wastewater treatment). Since the 1980s, HELCOM has worked with the 50% reduction targets for nutrients and discharges. Several countries have recently agreed to substantially reduce fertilizer use in the region (Baltic Sea Action Plan). In 1990s, it became obvious that the important Baltic Sea fish stocks were in a poor state and the fisheries were not under satisfactory control. The International Baltic Sea Fishery Commission (IBSFC) reacted with several resolutions to reduce fishing mortality and improve selectivity for cod. The main initiatives were to improve control and enforcement to assure adherence to TACs, set TACs based on target fishing mortalities, introduce technical measures to improve selectivity, and seasonal closures of areas to protect the spawning stock. However, the overexploitation of cod resources continued: the scientific advice was disregarded when setting quotas and the quotas restricting exploitation were not enforced.

In 1999, a Long-Term Management Strategy for Cod Stocks in the Baltic Sea was made including e.g. efforts to maintain a minimum spawning-stock biomass. The Recovery Plan for Baltic Sea Cod was developed in 2001 requiring a.o. seasonal closures and ban on fishing on the cod spawning grounds. Still, the problems remained and in 2004 it was acknowledged that the state of the cod stock had not improved, requiring determined action based on scientific advice. The EU agreed a plan for the Baltic Sea cod in 2007. In 2009 and 2010, The European Council Regulation for the Baltic TAC involved reductions in the number of fishing days per year. The cod fisheries are regulated by a seasonal closure to protect spawning fish. A year-round area closure for all fisheries in specific parts of the Bornholm Deep, the Gotland Basin and the Gdansk Deep was introduced in 2005.

High-grading has been prohibited since 2010 in all Baltic fisheries. In 2003, the minimum landing size was raised from 35 cm to 38 cm to protect the juvenile cods, which have not had a chance to reproduce yet. Additionally, fishing nets with exit windows have been introduced. To combat illegal fishing EU Commission has made inspections on randomly selected vessels and concluded that illegal fishing is substantial and practiced by many Baltic Sea countries. 

Key References

  1. Coulson A. 1982. Tanzania: A Political Economy. Oxford University Press: Oxford.
  2. Enfors I, Gordon L. 2007. Analysing Resilience In Dryland Agro-Ecosystems: A case study of the Makanya Catchment In Tanzania Over The Past 50 Years. Land Degrad. Develop. 18: 680-696 (2007).
  3. Enfors, I. 2009. Traps andTransformations: Exploring the potential of Water System Innovations in Dry-land sub-Saharan Africa. Doctoral thesis in natural resource management. ISBN 978-91-7155-863-3 pp. 1-56, US-AB, Stockholm
  4. Kikula I. 1998. Policy Implications on the environment: The Case of villagization in Tanzania. Nordiska Afrikainstitutet: Uppsala
  5. Kimambo IN. 1996. Environmental control and hunger in the mountains and plains of nineteenth-century north-eastern Tanzania. In custodians of the land :Ecology and culture in the history of Tanzania, Maddox G, Giblin J, Kimambo I (eds). James Currey: London.
  6. Koning N, Smaling E. 2005. Environmental crisis or ‘lie of the hand’? The debate on soil degradation in Africa. Land Use Policy 22: 3-11.
  7. Koponen J. 1996. Population: A dependent variable. In Custodians of the land: Ecology and culture in the history of Tanzania, Maddox G, Giblin J, Kimambo I (eds). James Currey: London
  8. Liu, FM.,Y. Q. Wu, H.L. Xiao, and Q.Z. Gao. 2005. Rainwater harvesting agriculture and water-use efficiency in semi-arid regions in Gansu province, China. Outlook on agriculture 34:159-165
  9. Makurika, H., H. H. G. Savenije, S. Uhlenbrook, J. Rockstorm, and A. Senzanje. 2009. Investigating the water balance of on-farm techniques for improved crop productivity in rainfed -systems: A case study of the Makanya catchment, Tanzania. Physics and Chemistry of the Earth 34:93-98
  10. Makurika, H., H. H. G. Savenije, S. Uhlenbrook, J. Rocstrom, and A. Senzanje. 2007b. Towards a better understanding of water partitioning processes for improved smallholder rainfed -agricultural systems: A case study of the Makanya catchment, Tanzania. Physics and Chemistry of the Earth 32:1082-1089
  11. Mazvimavi, K. And S. Twomlow. In Press. Socioeconomic and institutional factors influencing adoption of conservation farming by vulnerable households in Zimbabwe Agricultural systems In press-corrected proof
  12. Rockström , J. 2003. Resilience building and water demand management for drought mitigation. Physics and Chemistry of the Earth 28: 869-877
  13. Rockström, J. 2003b. Water for food and nature in drought-prone tropics: vapour shift in rain-fed agriculture. Philosophical Transitions of the Royal Society of London 358: 1997-2009
  14. Rockström, J., P. Kaumbuto, J. Mwalley, A. W. Nzabi, M. Temesgen, L. Mawenya, J. Barron, J. Mutua, and S. Damgaard-Larsen. 2009. Conservation Farming Strategies in East and Southern Africa: Yields and Rain Water Productivity from On-Farm Action Research. Soil and Tillage Research 103: 23-32
  15. Rocström, J., J. Barron, and P. Fox. 2002. Rainwater management for increased productivity among small-holder farmers in drought-prone environments. Physics and Chemistry of the Earth 27: 949-959
  16. Shao J. 1986. The villagization program and the disruption of the ecological balance in Tanzania. Canadian Journal of African Studies-Revue Canadienne des Etudes Africaines
  17. UNEP/SEI. 2009. Rainwater harvesting: a lifeline for human well-being. UNEP, Nairobi
  18. Vohland, K. and B. Barry. 2009. A review of in situ rainwater harvesting ( RWH ) practices modifying landscape functions in African drylands. Agriculture, Ecosystems & Environment 131:119-127.

Citation

Johnny Musumbu Tshimpanga, Reinette (Oonsie) Biggs. Makanya catchment, Tanzania. In: Regime Shifts Database, www.regimeshifts.org. Last revised 2011-12-19 16:44:09 GMT.
Monday, 28 February 2011 20:39

Aldabra atoll, Seychelles

Written by Albert

Aldabra atoll, Seychelles

Main Contributors:

Albert Norström

Other Contributors:

Summary

The Aldabra atoll in the southern Seychelles has undergone a shift from scleractinian to softcoral dominance. Following mass-bleaching in 1997-1998, the Aldabra reef suffered large-scale mortality, as did most shallow reef communities in the western Indian Ocean. Prior to the mass-bleaching event of 1998, soft corals comprised only 3 % of the reef. Annual monitoring of the Aldabra atoll reefs since 1998 indicate no signs of recovery of hard corals. The only organism group that has been exhibiting significant changes in abundance are soft corals. Soft corals become the dominant benthic category (28 % cover) in the shallow coral communities by 2004. An interesting aspect of this regime shift is that Aldabra atoll has escaped most direct human impacts, due to its isolated geographic position and its status as a UNESCO world heritage site.

Type of regime shift

Ecosystem type

  • Marine & coastal

Land uses

  • Conservation

Spatial scale of the case study

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

Continent or Ocean

  • Indian Ocean

Region

  • Indian Ocean

Countries

  • Seychelles

Locate with Google Map

Alternate regimes

The cod-dominated regime

The cod-dominated regime was characterized by abundant cod stocks, not only in the southern part of the Baltic Sea, but also further north and closer to shore. Cod predation regulated the number of sprat and herring. Pseudocalanus spp. dominated the zooplankton community. This regime was observed primarily during the early- to mid-1980s. 

Sprat-dominated regime

The sprat-dominated regime came into effect in 1989. A lower cod stock, an increased number of sprat and favorable conditions for sprat recruitment characterize the regime. In zooplankton community, Acartia spp. and Temora longicornis are more abundant than Psedocalanus spp. It is suggested that sprat's high predation on zooplankton lead to algal growth and declining oxygen content in deep waters. The high fishing pressure on cod is preventing the recovery of the stock and allowing the sprat to control the zooplankton. 

Drivers and causes of the regime shift

The key drivers for the Central Baltic cod-dominated regime to shift to a sprat-dominated regime are suggested to be poor cod recruitment conditions and too high fishing pressure caused by eutrophication, altered deep water conditions, infrequent inflows of North Sea saline waters and international fishing policies.

Climate functions as an indirect driver through changes in the physical environment and altered food supply for early stages. Decreased salinity, increased temperature and high sprat-predation pressure might have caused the regime subshift from Pseudocalanus spp. to Acartia spp. and Temora longicornis. Low salinity and oxygen conditions decrease the amount of the main prey of cod larvae. Higher temperatures support sprat recruitment by improving egg survival and food supply as Acartia spp. and Temora longicornis increase. 

How the regime shift worked

Cod is the main predator of sprat. It has been suggested that the large cod stock was able to control the sprat stock in the cod-dominated regime. Anthropogenic eutrophication and infrequent inflows of saline water from the North Sea contributed to increased anoxia and lowered salinity in the Central Baltic. Due to low salinity and oxygen content in the spawning areas, cod reproduction rates have remained low since the early 1980s. Deep water anoxia is a chronic stress for the survival of the cod eggs. Baltic cod needs salinity for the eggs to float in the water. If the required salinity is in anoxic conditions, eggs die.

Anoxia is one of the effects of the Baltic Sea eutrophication, but it can be temporarily reduced by inflows of North Sea saline waters, which replenish the deep-water layers of the Baltic Sea with saline and well-oxygenated water. Major Baltic Inflows decreased frequently in the early 1980s and there was a stagnation period until the early 1990s. Although the cod stock decreased due to cod recruitment decline caused by degraded environmental conditions, the fishing effort remained high. Unfavorable cod recruitment conditions and high fishing pressure caused a remarkable drop in cod biomass. As the Central Baltic Sea is characterized by simple food web with low species diversity, cod decrease allowed its' prey sprat to increase. Cod fishing further reduced the stock, making cod even more sensitive to adverse environmental conditions. International fishing quotas have been set to limit the cod fishing but they have not always been followed. The quotas have consistently been greater than the scientific recommendations.

Studies suggest that the large increase of the sprat stock has changed the system from mainly bottom-up to top-down trophic control. A trophic cascade occurred as the sprat stock dramatically increased. High sprat abundance changed the quantity and quality of zooplankton, which feeds on phytoplankton. A sub-shift in zooplankton species can be observed to have happened until the end of the 1980s: a shift in dominance occurred from Pseudocalanus spp., the main food supply for cod larvae, to the main food supply of sprat larvae and adults, Acartia spp. and Temora longicornis. Salinity, temperature, predation of sprat, herring and mysids and climate in general regulate the zooplankton species as they all have their specific abiotic preferences. Through trophic cascades large sprat stock also lead to higher phytoplankton biomass and algal blooms during summer. Algae growth promotes further anoxia. A sprat-dominated food web has been suggested to stabilize the cod stock by sprat predating on cod eggs and larvae, and through sprat competing with young cod for zooplankton resources. Changed abundance of sprat may have even been reflected to the top levels of the Baltic food web: the condition of Common Murre (Uria aalge) chicks seem to increase and decrease in relation to sprat stock. This way human exploitation combined to natural changes caused variations in several trophic levels, which altered the ecosystem functioning as the interaction between species changed.

 

Impacts on ecosystem services and human well-being

The main ecosystem services associated with the cod-dominated regime were commercially viable, high value cod stocks, recreational value of large cod stocks and a sustainable small-scale fishing sector favoring regional development. The regime was possibly related to high water quality stimulating tourism development. Cod provide the Baltic Sea region with provisioning services: Cod is commercially the most important species in the Baltic Sea for a large number of fishermen. In the sprat-dominated region, the economic value of the catch for human consumption decreases due to the relative composition of the fish species. Being a predator at the top of the food chain, cod provides the Baltic Sea with regulating ecosystem services: cod reduces sprat, which prey on zooplankton and early life stages of cod. The high summer levels of phytoplankton could partly be a result of the sprat predation-induced decrease in total zooplankton biomass. The decay of increased algae leads to oxygen deficit and thereby causes damage to the biodiversity. The regulating role of cod may also be reflected to the top levels of the Baltic food web, the sea birds. The sprat-dominated regime is dominated by low value fish used for reduction fisheries and international fish meal and fish oil markets. These large-scale fisheries are mainly based outside the Baltic Sea region, which makes the regime less advantageous for the local development. The sprat-dominated regime may be associated with cascading effects on water quality as the low biomass of summer zooplankton may increase the probability for cyanobacterial blooms.

Low cod biomass makes industrial fishing and businesses associated with recreational fishing less profitable. Increased occurrence of algal blooms makes the Baltic Sea less attractive for tourists and recreation. From the socioeconomic perspective, tourist industry is more important than fishing industry in for example Sweden. The Baltic Sea environment and its cultural fishing surroundings are important tourist attractions. The toxic blooms and low water quality are nuisance for coastal property owners, local enterprises, bathers and others seeking for creation on the coasts. 

Management options

The goal for managing the regime shift is to maintain the resilience of the Baltic Sea ecosystem by targeting eutrophication and recovery of the cod stock. The management actions to reduce nutrient pollution began in the 1970s, when Helsinki Commission (HELCOM) adopted several recommendations for all sectors (industry, agriculture, wastewater treatment). Since the 1980s, HELCOM has worked with the 50% reduction targets for nutrients and discharges. Several countries have recently agreed to substantially reduce fertilizer use in the region (Baltic Sea Action Plan). In 1990s, it became obvious that the important Baltic Sea fish stocks were in a poor state and the fisheries were not under satisfactory control. The International Baltic Sea Fishery Commission (IBSFC) reacted with several resolutions to reduce fishing mortality and improve selectivity for cod. The main initiatives were to improve control and enforcement to assure adherence to TACs, set TACs based on target fishing mortalities, introduce technical measures to improve selectivity, and seasonal closures of areas to protect the spawning stock. However, the overexploitation of cod resources continued: the scientific advice was disregarded when setting quotas and the quotas restricting exploitation were not enforced.

In 1999, a Long-Term Management Strategy for Cod Stocks in the Baltic Sea was made including e.g. efforts to maintain a minimum spawning-stock biomass. The Recovery Plan for Baltic Sea Cod was developed in 2001 requiring a.o. seasonal closures and ban on fishing on the cod spawning grounds. Still, the problems remained and in 2004 it was acknowledged that the state of the cod stock had not improved, requiring determined action based on scientific advice. The EU agreed a plan for the Baltic Sea cod in 2007. In 2009 and 2010, The European Council Regulation for the Baltic TAC involved reductions in the number of fishing days per year. The cod fisheries are regulated by a seasonal closure to protect spawning fish. A year-round area closure for all fisheries in specific parts of the Bornholm Deep, the Gotland Basin and the Gdansk Deep was introduced in 2005.

High-grading has been prohibited since 2010 in all Baltic fisheries. In 2003, the minimum landing size was raised from 35 cm to 38 cm to protect the juvenile cods, which have not had a chance to reproduce yet. Additionally, fishing nets with exit windows have been introduced. To combat illegal fishing EU Commission has made inspections on randomly selected vessels and concluded that illegal fishing is substantial and practiced by many Baltic Sea countries. 

Key References

  1. Norström AV, Nyström M, Lokrantz J, Folke C. 2009. Alternative states on coral reefs: beyond coral-macroalgal phase shifts. Marine Ecology-Progress Series 376, 295-306
  2. Stobart B, Teleki K, Buckley R, Downing N, Callow M. 2005. Coral recovery at Aldabra Atoll, Seychelles: five years after the 1998 bleaching event. Philosophical Transactions of the Royal Society B 363, 251-255

Citation

Albert Norström. Aldabra atoll, Seychelles. In: Regime Shifts Database, www.regimeshifts.org. Last revised 2011-03-03 10:12:00 GMT.
Monday, 28 February 2011 20:08

Jamaican coral reefs

Written by Albert

Jamaican coral reefs

Main Contributors:

Albert Norström

Other Contributors:

Summary

The archetypical example of a coral reef regime shift is the dramatic transition from coral dominance (52% coral cover, 4% algal cover) to macroalgal dominance (2% coral cover, 92% algal cover) which occurred on Jamaican reefs in the 1980s as a result of the synergistic impacts of overfishing, hurricane damage and disease. Similar examples of coral-macroalgae shifts have been observed across the Caribbean region, throughout the Eastern-Pacific, Indian Ocean and on the Great Barrier Reef.

Type of regime shift

Ecosystem type

  • Marine & coastal

Land uses

  • Large-scale commercial crop cultivation
  • Fisheries
  • Mining
  • Tourism

Spatial scale of the case study

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

Continent or Ocean

  • North America

Region

  • Caribbean

Countries

  • Jamaica

Locate with Google Map

Alternate regimes

The cod-dominated regime

The cod-dominated regime was characterized by abundant cod stocks, not only in the southern part of the Baltic Sea, but also further north and closer to shore. Cod predation regulated the number of sprat and herring. Pseudocalanus spp. dominated the zooplankton community. This regime was observed primarily during the early- to mid-1980s. 

Sprat-dominated regime

The sprat-dominated regime came into effect in 1989. A lower cod stock, an increased number of sprat and favorable conditions for sprat recruitment characterize the regime. In zooplankton community, Acartia spp. and Temora longicornis are more abundant than Psedocalanus spp. It is suggested that sprat's high predation on zooplankton lead to algal growth and declining oxygen content in deep waters. The high fishing pressure on cod is preventing the recovery of the stock and allowing the sprat to control the zooplankton. 

Drivers and causes of the regime shift

The key drivers for the Central Baltic cod-dominated regime to shift to a sprat-dominated regime are suggested to be poor cod recruitment conditions and too high fishing pressure caused by eutrophication, altered deep water conditions, infrequent inflows of North Sea saline waters and international fishing policies.

Climate functions as an indirect driver through changes in the physical environment and altered food supply for early stages. Decreased salinity, increased temperature and high sprat-predation pressure might have caused the regime subshift from Pseudocalanus spp. to Acartia spp. and Temora longicornis. Low salinity and oxygen conditions decrease the amount of the main prey of cod larvae. Higher temperatures support sprat recruitment by improving egg survival and food supply as Acartia spp. and Temora longicornis increase. 

How the regime shift worked

Cod is the main predator of sprat. It has been suggested that the large cod stock was able to control the sprat stock in the cod-dominated regime. Anthropogenic eutrophication and infrequent inflows of saline water from the North Sea contributed to increased anoxia and lowered salinity in the Central Baltic. Due to low salinity and oxygen content in the spawning areas, cod reproduction rates have remained low since the early 1980s. Deep water anoxia is a chronic stress for the survival of the cod eggs. Baltic cod needs salinity for the eggs to float in the water. If the required salinity is in anoxic conditions, eggs die.

Anoxia is one of the effects of the Baltic Sea eutrophication, but it can be temporarily reduced by inflows of North Sea saline waters, which replenish the deep-water layers of the Baltic Sea with saline and well-oxygenated water. Major Baltic Inflows decreased frequently in the early 1980s and there was a stagnation period until the early 1990s. Although the cod stock decreased due to cod recruitment decline caused by degraded environmental conditions, the fishing effort remained high. Unfavorable cod recruitment conditions and high fishing pressure caused a remarkable drop in cod biomass. As the Central Baltic Sea is characterized by simple food web with low species diversity, cod decrease allowed its' prey sprat to increase. Cod fishing further reduced the stock, making cod even more sensitive to adverse environmental conditions. International fishing quotas have been set to limit the cod fishing but they have not always been followed. The quotas have consistently been greater than the scientific recommendations.

Studies suggest that the large increase of the sprat stock has changed the system from mainly bottom-up to top-down trophic control. A trophic cascade occurred as the sprat stock dramatically increased. High sprat abundance changed the quantity and quality of zooplankton, which feeds on phytoplankton. A sub-shift in zooplankton species can be observed to have happened until the end of the 1980s: a shift in dominance occurred from Pseudocalanus spp., the main food supply for cod larvae, to the main food supply of sprat larvae and adults, Acartia spp. and Temora longicornis. Salinity, temperature, predation of sprat, herring and mysids and climate in general regulate the zooplankton species as they all have their specific abiotic preferences. Through trophic cascades large sprat stock also lead to higher phytoplankton biomass and algal blooms during summer. Algae growth promotes further anoxia. A sprat-dominated food web has been suggested to stabilize the cod stock by sprat predating on cod eggs and larvae, and through sprat competing with young cod for zooplankton resources. Changed abundance of sprat may have even been reflected to the top levels of the Baltic food web: the condition of Common Murre (Uria aalge) chicks seem to increase and decrease in relation to sprat stock. This way human exploitation combined to natural changes caused variations in several trophic levels, which altered the ecosystem functioning as the interaction between species changed.

 

Impacts on ecosystem services and human well-being

The main ecosystem services associated with the cod-dominated regime were commercially viable, high value cod stocks, recreational value of large cod stocks and a sustainable small-scale fishing sector favoring regional development. The regime was possibly related to high water quality stimulating tourism development. Cod provide the Baltic Sea region with provisioning services: Cod is commercially the most important species in the Baltic Sea for a large number of fishermen. In the sprat-dominated region, the economic value of the catch for human consumption decreases due to the relative composition of the fish species. Being a predator at the top of the food chain, cod provides the Baltic Sea with regulating ecosystem services: cod reduces sprat, which prey on zooplankton and early life stages of cod. The high summer levels of phytoplankton could partly be a result of the sprat predation-induced decrease in total zooplankton biomass. The decay of increased algae leads to oxygen deficit and thereby causes damage to the biodiversity. The regulating role of cod may also be reflected to the top levels of the Baltic food web, the sea birds. The sprat-dominated regime is dominated by low value fish used for reduction fisheries and international fish meal and fish oil markets. These large-scale fisheries are mainly based outside the Baltic Sea region, which makes the regime less advantageous for the local development. The sprat-dominated regime may be associated with cascading effects on water quality as the low biomass of summer zooplankton may increase the probability for cyanobacterial blooms.

Low cod biomass makes industrial fishing and businesses associated with recreational fishing less profitable. Increased occurrence of algal blooms makes the Baltic Sea less attractive for tourists and recreation. From the socioeconomic perspective, tourist industry is more important than fishing industry in for example Sweden. The Baltic Sea environment and its cultural fishing surroundings are important tourist attractions. The toxic blooms and low water quality are nuisance for coastal property owners, local enterprises, bathers and others seeking for creation on the coasts. 

Management options

The goal for managing the regime shift is to maintain the resilience of the Baltic Sea ecosystem by targeting eutrophication and recovery of the cod stock. The management actions to reduce nutrient pollution began in the 1970s, when Helsinki Commission (HELCOM) adopted several recommendations for all sectors (industry, agriculture, wastewater treatment). Since the 1980s, HELCOM has worked with the 50% reduction targets for nutrients and discharges. Several countries have recently agreed to substantially reduce fertilizer use in the region (Baltic Sea Action Plan). In 1990s, it became obvious that the important Baltic Sea fish stocks were in a poor state and the fisheries were not under satisfactory control. The International Baltic Sea Fishery Commission (IBSFC) reacted with several resolutions to reduce fishing mortality and improve selectivity for cod. The main initiatives were to improve control and enforcement to assure adherence to TACs, set TACs based on target fishing mortalities, introduce technical measures to improve selectivity, and seasonal closures of areas to protect the spawning stock. However, the overexploitation of cod resources continued: the scientific advice was disregarded when setting quotas and the quotas restricting exploitation were not enforced.

In 1999, a Long-Term Management Strategy for Cod Stocks in the Baltic Sea was made including e.g. efforts to maintain a minimum spawning-stock biomass. The Recovery Plan for Baltic Sea Cod was developed in 2001 requiring a.o. seasonal closures and ban on fishing on the cod spawning grounds. Still, the problems remained and in 2004 it was acknowledged that the state of the cod stock had not improved, requiring determined action based on scientific advice. The EU agreed a plan for the Baltic Sea cod in 2007. In 2009 and 2010, The European Council Regulation for the Baltic TAC involved reductions in the number of fishing days per year. The cod fisheries are regulated by a seasonal closure to protect spawning fish. A year-round area closure for all fisheries in specific parts of the Bornholm Deep, the Gotland Basin and the Gdansk Deep was introduced in 2005.

High-grading has been prohibited since 2010 in all Baltic fisheries. In 2003, the minimum landing size was raised from 35 cm to 38 cm to protect the juvenile cods, which have not had a chance to reproduce yet. Additionally, fishing nets with exit windows have been introduced. To combat illegal fishing EU Commission has made inspections on randomly selected vessels and concluded that illegal fishing is substantial and practiced by many Baltic Sea countries. 

Key References

  1. Hughes TP. 1994. Catastrophes, phase-shifts, and large-scale degradation of a Caribbean coral reef. Science 265, 1547-1551.

Citation

Albert Norström. Jamaican coral reefs. In: Regime Shifts Database, www.regimeshifts.org. Last revised 2011-03-03 10:08:25 GMT.
Saturday, 26 February 2011 11:15

Lake Mendota, Wisconsin, USA

Written by Reinette (Oonsie) Biggs

Lake Mendota, Wisconsin, USA

Main Contributors:

Reinette (Oonsie) Biggs

Other Contributors:

Summary

Lake Mendota is located in south central Wisconsin in the Upper Rock Watershed. It has been called the most studied lake in the world and has been studied since the 1880’s. Cyanobacterial blooms have been reported on Lake Mendota as early as 1976 with a very severe bloom in the spring of 1990. Many efforts have been made to reduce the frequency of harmful algal blooms on Lake Mendota.

Type of regime shift

Ecosystem type

  • Freshwater lakes & rivers

Land uses

  • Urban
  • Large-scale commercial crop cultivation

Spatial scale of the case study

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

Continent or Ocean

  • North America

Region

  • Wisconsin

Countries

  • United States

Locate with Google Map

Alternate regimes

The cod-dominated regime

The cod-dominated regime was characterized by abundant cod stocks, not only in the southern part of the Baltic Sea, but also further north and closer to shore. Cod predation regulated the number of sprat and herring. Pseudocalanus spp. dominated the zooplankton community. This regime was observed primarily during the early- to mid-1980s. 

Sprat-dominated regime

The sprat-dominated regime came into effect in 1989. A lower cod stock, an increased number of sprat and favorable conditions for sprat recruitment characterize the regime. In zooplankton community, Acartia spp. and Temora longicornis are more abundant than Psedocalanus spp. It is suggested that sprat's high predation on zooplankton lead to algal growth and declining oxygen content in deep waters. The high fishing pressure on cod is preventing the recovery of the stock and allowing the sprat to control the zooplankton. 

Drivers and causes of the regime shift

The key drivers for the Central Baltic cod-dominated regime to shift to a sprat-dominated regime are suggested to be poor cod recruitment conditions and too high fishing pressure caused by eutrophication, altered deep water conditions, infrequent inflows of North Sea saline waters and international fishing policies.

Climate functions as an indirect driver through changes in the physical environment and altered food supply for early stages. Decreased salinity, increased temperature and high sprat-predation pressure might have caused the regime subshift from Pseudocalanus spp. to Acartia spp. and Temora longicornis. Low salinity and oxygen conditions decrease the amount of the main prey of cod larvae. Higher temperatures support sprat recruitment by improving egg survival and food supply as Acartia spp. and Temora longicornis increase. 

How the regime shift worked

Cod is the main predator of sprat. It has been suggested that the large cod stock was able to control the sprat stock in the cod-dominated regime. Anthropogenic eutrophication and infrequent inflows of saline water from the North Sea contributed to increased anoxia and lowered salinity in the Central Baltic. Due to low salinity and oxygen content in the spawning areas, cod reproduction rates have remained low since the early 1980s. Deep water anoxia is a chronic stress for the survival of the cod eggs. Baltic cod needs salinity for the eggs to float in the water. If the required salinity is in anoxic conditions, eggs die.

Anoxia is one of the effects of the Baltic Sea eutrophication, but it can be temporarily reduced by inflows of North Sea saline waters, which replenish the deep-water layers of the Baltic Sea with saline and well-oxygenated water. Major Baltic Inflows decreased frequently in the early 1980s and there was a stagnation period until the early 1990s. Although the cod stock decreased due to cod recruitment decline caused by degraded environmental conditions, the fishing effort remained high. Unfavorable cod recruitment conditions and high fishing pressure caused a remarkable drop in cod biomass. As the Central Baltic Sea is characterized by simple food web with low species diversity, cod decrease allowed its' prey sprat to increase. Cod fishing further reduced the stock, making cod even more sensitive to adverse environmental conditions. International fishing quotas have been set to limit the cod fishing but they have not always been followed. The quotas have consistently been greater than the scientific recommendations.

Studies suggest that the large increase of the sprat stock has changed the system from mainly bottom-up to top-down trophic control. A trophic cascade occurred as the sprat stock dramatically increased. High sprat abundance changed the quantity and quality of zooplankton, which feeds on phytoplankton. A sub-shift in zooplankton species can be observed to have happened until the end of the 1980s: a shift in dominance occurred from Pseudocalanus spp., the main food supply for cod larvae, to the main food supply of sprat larvae and adults, Acartia spp. and Temora longicornis. Salinity, temperature, predation of sprat, herring and mysids and climate in general regulate the zooplankton species as they all have their specific abiotic preferences. Through trophic cascades large sprat stock also lead to higher phytoplankton biomass and algal blooms during summer. Algae growth promotes further anoxia. A sprat-dominated food web has been suggested to stabilize the cod stock by sprat predating on cod eggs and larvae, and through sprat competing with young cod for zooplankton resources. Changed abundance of sprat may have even been reflected to the top levels of the Baltic food web: the condition of Common Murre (Uria aalge) chicks seem to increase and decrease in relation to sprat stock. This way human exploitation combined to natural changes caused variations in several trophic levels, which altered the ecosystem functioning as the interaction between species changed.

 

Impacts on ecosystem services and human well-being

The main ecosystem services associated with the cod-dominated regime were commercially viable, high value cod stocks, recreational value of large cod stocks and a sustainable small-scale fishing sector favoring regional development. The regime was possibly related to high water quality stimulating tourism development. Cod provide the Baltic Sea region with provisioning services: Cod is commercially the most important species in the Baltic Sea for a large number of fishermen. In the sprat-dominated region, the economic value of the catch for human consumption decreases due to the relative composition of the fish species. Being a predator at the top of the food chain, cod provides the Baltic Sea with regulating ecosystem services: cod reduces sprat, which prey on zooplankton and early life stages of cod. The high summer levels of phytoplankton could partly be a result of the sprat predation-induced decrease in total zooplankton biomass. The decay of increased algae leads to oxygen deficit and thereby causes damage to the biodiversity. The regulating role of cod may also be reflected to the top levels of the Baltic food web, the sea birds. The sprat-dominated regime is dominated by low value fish used for reduction fisheries and international fish meal and fish oil markets. These large-scale fisheries are mainly based outside the Baltic Sea region, which makes the regime less advantageous for the local development. The sprat-dominated regime may be associated with cascading effects on water quality as the low biomass of summer zooplankton may increase the probability for cyanobacterial blooms.

Low cod biomass makes industrial fishing and businesses associated with recreational fishing less profitable. Increased occurrence of algal blooms makes the Baltic Sea less attractive for tourists and recreation. From the socioeconomic perspective, tourist industry is more important than fishing industry in for example Sweden. The Baltic Sea environment and its cultural fishing surroundings are important tourist attractions. The toxic blooms and low water quality are nuisance for coastal property owners, local enterprises, bathers and others seeking for creation on the coasts. 

Management options

The goal for managing the regime shift is to maintain the resilience of the Baltic Sea ecosystem by targeting eutrophication and recovery of the cod stock. The management actions to reduce nutrient pollution began in the 1970s, when Helsinki Commission (HELCOM) adopted several recommendations for all sectors (industry, agriculture, wastewater treatment). Since the 1980s, HELCOM has worked with the 50% reduction targets for nutrients and discharges. Several countries have recently agreed to substantially reduce fertilizer use in the region (Baltic Sea Action Plan). In 1990s, it became obvious that the important Baltic Sea fish stocks were in a poor state and the fisheries were not under satisfactory control. The International Baltic Sea Fishery Commission (IBSFC) reacted with several resolutions to reduce fishing mortality and improve selectivity for cod. The main initiatives were to improve control and enforcement to assure adherence to TACs, set TACs based on target fishing mortalities, introduce technical measures to improve selectivity, and seasonal closures of areas to protect the spawning stock. However, the overexploitation of cod resources continued: the scientific advice was disregarded when setting quotas and the quotas restricting exploitation were not enforced.

In 1999, a Long-Term Management Strategy for Cod Stocks in the Baltic Sea was made including e.g. efforts to maintain a minimum spawning-stock biomass. The Recovery Plan for Baltic Sea Cod was developed in 2001 requiring a.o. seasonal closures and ban on fishing on the cod spawning grounds. Still, the problems remained and in 2004 it was acknowledged that the state of the cod stock had not improved, requiring determined action based on scientific advice. The EU agreed a plan for the Baltic Sea cod in 2007. In 2009 and 2010, The European Council Regulation for the Baltic TAC involved reductions in the number of fishing days per year. The cod fisheries are regulated by a seasonal closure to protect spawning fish. A year-round area closure for all fisheries in specific parts of the Bornholm Deep, the Gotland Basin and the Gdansk Deep was introduced in 2005.

High-grading has been prohibited since 2010 in all Baltic fisheries. In 2003, the minimum landing size was raised from 35 cm to 38 cm to protect the juvenile cods, which have not had a chance to reproduce yet. Additionally, fishing nets with exit windows have been introduced. To combat illegal fishing EU Commission has made inspections on randomly selected vessels and concluded that illegal fishing is substantial and practiced by many Baltic Sea countries. 

Key References

  1. Carpenter SR, et al. 2006. Understanding regional change: comparison of two lake districts. BioScience
  2. Carpenter SR, Lathrop RC, Nowak P, Bennett EM, Reed T, Soranno PA. 2006b. The ongoing experiment: Restoration of Lake Mendota and its watershed. In Magnuson JJ, Kratz TK, Benson BJ, eds. Long-term dynamics of lakes in the landscape: Long-term ecological research on north temperate lakes. Oxford, UK: Oxford University Press.
  3. Carpenter SR. 2003. Regime shifts in lake ecosystems: pattern and variation. Oldendorf/Luhe, Germany: International Ecology Institute.
  4. http://lakemendota.uwcfl.org/lake-mendota/

Citation

Reinette (Oonsie) Biggs. Lake Mendota, Wisconsin, USA. In: Regime Shifts Database, www.regimeshifts.org. Last revised 2012-03-17 19:16:32 GMT.
Friday, 25 February 2011 09:45

Balinese rice production

Written by Daniel

Balinese rice production

Main Contributors:

Caroline Schill, Ylva Ran, Daniel Ospina

Other Contributors:

Reinette (Oonsie) Biggs, -1

Summary

As described by Lansing (1991 and others) for roughly a thousand years, rice farming in southern Bali (Indonesia) has operated through a religious and water-irrigation institutional arrangement of Subaks and Water Temples, which coordinate water use and generate landscape-level pest control. During the 1970s, the Indonesian government decided to carry-out a Green Revolution to face the challenge of an increasing internal population demanding more food. Several changes at different levels where introduced: high-yielding varieties of rice were distributed among the farmers, together with a tech-package of pesticides and fertilizers; and the water temples were restricted from regulating water distribution. After a couple of decades of successful increase in production, problems regarding water distribution and pest outbreaks, lead to the recognition of the functional role of Subaks and Water Temples in managing these two factors, so the Indonesian government withdrew the restriction. However, an important percentage of farmers decided to continue using the high-yielding rice varieties, together with pesticides and fertilizers. Given that this agricultural tech-package costs money, the ‘rice production – cash income’ feedback gained strength over ‘rice production – subsistence’, which dominated before the Green Revolution, and was sustained by a variety of agricultural practices that articulated in a more complex form. Cultural and economic dimensions of globalization set the context for this shift, with an increasing importance of money in mediating local social relations, and a slow change in world-views, beliefs and values. Possible negative effects of this farm-level shift in agricultural practices are a fast degradation of soil quality and an increased input of phosphorus to the sea by runoff.

Type of regime shift

  • Unknown

Ecosystem type

  • Tropical Forests

Land uses

  • Small-scale subsistence crop cultivation
  • Tourism

Spatial scale of the case study

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

Continent or Ocean

  • Indian Ocean

Region

  • Southern Bali

Countries

  • Indonesia

Locate with Google Map

Drivers

Key direct drivers

  • Harvest and resource consumption
  • External inputs (eg fertilizers)
  • Species introduction or removal

Impacts

Ecosystem type

  • Marine & coastal

Key Ecosystem Processes

  • Nutrient cycling
  • Water cycling

Biodiversity

  • Biodiversity

Provisioning services

  • Fisheries

Regulating services

  • Water purification

Cultural services

  • Recreation
  • Aesthetic values

Human Well-being

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

Key Attributes

Spatial scale of RS

  • Sub-continental/regional

Time scale of RS

  • Years
  • Decades

Reversibility

  • Unknown

Evidence

  • Models
  • Contemporary observations
  • Experiments

Confidence: Existence of RS

  • Contested – Reasonable evidence both for and against the existence of RS

Confidence: Mechanism underlying RS

  • Contested – Multiple proposed mechanisms, reasonable evidence both for and against different mechanisms

Alternate regimes

The cod-dominated regime

The cod-dominated regime was characterized by abundant cod stocks, not only in the southern part of the Baltic Sea, but also further north and closer to shore. Cod predation regulated the number of sprat and herring. Pseudocalanus spp. dominated the zooplankton community. This regime was observed primarily during the early- to mid-1980s. 

Sprat-dominated regime

The sprat-dominated regime came into effect in 1989. A lower cod stock, an increased number of sprat and favorable conditions for sprat recruitment characterize the regime. In zooplankton community, Acartia spp. and Temora longicornis are more abundant than Psedocalanus spp. It is suggested that sprat's high predation on zooplankton lead to algal growth and declining oxygen content in deep waters. The high fishing pressure on cod is preventing the recovery of the stock and allowing the sprat to control the zooplankton. 

Drivers and causes of the regime shift

The key drivers for the Central Baltic cod-dominated regime to shift to a sprat-dominated regime are suggested to be poor cod recruitment conditions and too high fishing pressure caused by eutrophication, altered deep water conditions, infrequent inflows of North Sea saline waters and international fishing policies.

Climate functions as an indirect driver through changes in the physical environment and altered food supply for early stages. Decreased salinity, increased temperature and high sprat-predation pressure might have caused the regime subshift from Pseudocalanus spp. to Acartia spp. and Temora longicornis. Low salinity and oxygen conditions decrease the amount of the main prey of cod larvae. Higher temperatures support sprat recruitment by improving egg survival and food supply as Acartia spp. and Temora longicornis increase. 

How the regime shift worked

Cod is the main predator of sprat. It has been suggested that the large cod stock was able to control the sprat stock in the cod-dominated regime. Anthropogenic eutrophication and infrequent inflows of saline water from the North Sea contributed to increased anoxia and lowered salinity in the Central Baltic. Due to low salinity and oxygen content in the spawning areas, cod reproduction rates have remained low since the early 1980s. Deep water anoxia is a chronic stress for the survival of the cod eggs. Baltic cod needs salinity for the eggs to float in the water. If the required salinity is in anoxic conditions, eggs die.

Anoxia is one of the effects of the Baltic Sea eutrophication, but it can be temporarily reduced by inflows of North Sea saline waters, which replenish the deep-water layers of the Baltic Sea with saline and well-oxygenated water. Major Baltic Inflows decreased frequently in the early 1980s and there was a stagnation period until the early 1990s. Although the cod stock decreased due to cod recruitment decline caused by degraded environmental conditions, the fishing effort remained high. Unfavorable cod recruitment conditions and high fishing pressure caused a remarkable drop in cod biomass. As the Central Baltic Sea is characterized by simple food web with low species diversity, cod decrease allowed its' prey sprat to increase. Cod fishing further reduced the stock, making cod even more sensitive to adverse environmental conditions. International fishing quotas have been set to limit the cod fishing but they have not always been followed. The quotas have consistently been greater than the scientific recommendations.

Studies suggest that the large increase of the sprat stock has changed the system from mainly bottom-up to top-down trophic control. A trophic cascade occurred as the sprat stock dramatically increased. High sprat abundance changed the quantity and quality of zooplankton, which feeds on phytoplankton. A sub-shift in zooplankton species can be observed to have happened until the end of the 1980s: a shift in dominance occurred from Pseudocalanus spp., the main food supply for cod larvae, to the main food supply of sprat larvae and adults, Acartia spp. and Temora longicornis. Salinity, temperature, predation of sprat, herring and mysids and climate in general regulate the zooplankton species as they all have their specific abiotic preferences. Through trophic cascades large sprat stock also lead to higher phytoplankton biomass and algal blooms during summer. Algae growth promotes further anoxia. A sprat-dominated food web has been suggested to stabilize the cod stock by sprat predating on cod eggs and larvae, and through sprat competing with young cod for zooplankton resources. Changed abundance of sprat may have even been reflected to the top levels of the Baltic food web: the condition of Common Murre (Uria aalge) chicks seem to increase and decrease in relation to sprat stock. This way human exploitation combined to natural changes caused variations in several trophic levels, which altered the ecosystem functioning as the interaction between species changed.

 

Impacts on ecosystem services and human well-being

The main ecosystem services associated with the cod-dominated regime were commercially viable, high value cod stocks, recreational value of large cod stocks and a sustainable small-scale fishing sector favoring regional development. The regime was possibly related to high water quality stimulating tourism development. Cod provide the Baltic Sea region with provisioning services: Cod is commercially the most important species in the Baltic Sea for a large number of fishermen. In the sprat-dominated region, the economic value of the catch for human consumption decreases due to the relative composition of the fish species. Being a predator at the top of the food chain, cod provides the Baltic Sea with regulating ecosystem services: cod reduces sprat, which prey on zooplankton and early life stages of cod. The high summer levels of phytoplankton could partly be a result of the sprat predation-induced decrease in total zooplankton biomass. The decay of increased algae leads to oxygen deficit and thereby causes damage to the biodiversity. The regulating role of cod may also be reflected to the top levels of the Baltic food web, the sea birds. The sprat-dominated regime is dominated by low value fish used for reduction fisheries and international fish meal and fish oil markets. These large-scale fisheries are mainly based outside the Baltic Sea region, which makes the regime less advantageous for the local development. The sprat-dominated regime may be associated with cascading effects on water quality as the low biomass of summer zooplankton may increase the probability for cyanobacterial blooms.

Low cod biomass makes industrial fishing and businesses associated with recreational fishing less profitable. Increased occurrence of algal blooms makes the Baltic Sea less attractive for tourists and recreation. From the socioeconomic perspective, tourist industry is more important than fishing industry in for example Sweden. The Baltic Sea environment and its cultural fishing surroundings are important tourist attractions. The toxic blooms and low water quality are nuisance for coastal property owners, local enterprises, bathers and others seeking for creation on the coasts. 

Management options

The goal for managing the regime shift is to maintain the resilience of the Baltic Sea ecosystem by targeting eutrophication and recovery of the cod stock. The management actions to reduce nutrient pollution began in the 1970s, when Helsinki Commission (HELCOM) adopted several recommendations for all sectors (industry, agriculture, wastewater treatment). Since the 1980s, HELCOM has worked with the 50% reduction targets for nutrients and discharges. Several countries have recently agreed to substantially reduce fertilizer use in the region (Baltic Sea Action Plan). In 1990s, it became obvious that the important Baltic Sea fish stocks were in a poor state and the fisheries were not under satisfactory control. The International Baltic Sea Fishery Commission (IBSFC) reacted with several resolutions to reduce fishing mortality and improve selectivity for cod. The main initiatives were to improve control and enforcement to assure adherence to TACs, set TACs based on target fishing mortalities, introduce technical measures to improve selectivity, and seasonal closures of areas to protect the spawning stock. However, the overexploitation of cod resources continued: the scientific advice was disregarded when setting quotas and the quotas restricting exploitation were not enforced.

In 1999, a Long-Term Management Strategy for Cod Stocks in the Baltic Sea was made including e.g. efforts to maintain a minimum spawning-stock biomass. The Recovery Plan for Baltic Sea Cod was developed in 2001 requiring a.o. seasonal closures and ban on fishing on the cod spawning grounds. Still, the problems remained and in 2004 it was acknowledged that the state of the cod stock had not improved, requiring determined action based on scientific advice. The EU agreed a plan for the Baltic Sea cod in 2007. In 2009 and 2010, The European Council Regulation for the Baltic TAC involved reductions in the number of fishing days per year. The cod fisheries are regulated by a seasonal closure to protect spawning fish. A year-round area closure for all fisheries in specific parts of the Bornholm Deep, the Gotland Basin and the Gdansk Deep was introduced in 2005.

High-grading has been prohibited since 2010 in all Baltic fisheries. In 2003, the minimum landing size was raised from 35 cm to 38 cm to protect the juvenile cods, which have not had a chance to reproduce yet. Additionally, fishing nets with exit windows have been introduced. To combat illegal fishing EU Commission has made inspections on randomly selected vessels and concluded that illegal fishing is substantial and practiced by many Baltic Sea countries. 

Alternate regimes

The cod-dominated regime

The cod-dominated regime was characterized by abundant cod stocks, not only in the southern part of the Baltic Sea, but also further north and closer to shore. Cod predation regulated the number of sprat and herring. Pseudocalanus spp. dominated the zooplankton community. This regime was observed primarily during the early- to mid-1980s. 

Sprat-dominated regime

The sprat-dominated regime came into effect in 1989. A lower cod stock, an increased number of sprat and favorable conditions for sprat recruitment characterize the regime. In zooplankton community, Acartia spp. and Temora longicornis are more abundant than Psedocalanus spp. It is suggested that sprat's high predation on zooplankton lead to algal growth and declining oxygen content in deep waters. The high fishing pressure on cod is preventing the recovery of the stock and allowing the sprat to control the zooplankton. 

Drivers and causes of the regime shift

The key drivers for the Central Baltic cod-dominated regime to shift to a sprat-dominated regime are suggested to be poor cod recruitment conditions and too high fishing pressure caused by eutrophication, altered deep water conditions, infrequent inflows of North Sea saline waters and international fishing policies.

Climate functions as an indirect driver through changes in the physical environment and altered food supply for early stages. Decreased salinity, increased temperature and high sprat-predation pressure might have caused the regime subshift from Pseudocalanus spp. to Acartia spp. and Temora longicornis. Low salinity and oxygen conditions decrease the amount of the main prey of cod larvae. Higher temperatures support sprat recruitment by improving egg survival and food supply as Acartia spp. and Temora longicornis increase. 

How the regime shift worked

Cod is the main predator of sprat. It has been suggested that the large cod stock was able to control the sprat stock in the cod-dominated regime. Anthropogenic eutrophication and infrequent inflows of saline water from the North Sea contributed to increased anoxia and lowered salinity in the Central Baltic. Due to low salinity and oxygen content in the spawning areas, cod reproduction rates have remained low since the early 1980s. Deep water anoxia is a chronic stress for the survival of the cod eggs. Baltic cod needs salinity for the eggs to float in the water. If the required salinity is in anoxic conditions, eggs die.

Anoxia is one of the effects of the Baltic Sea eutrophication, but it can be temporarily reduced by inflows of North Sea saline waters, which replenish the deep-water layers of the Baltic Sea with saline and well-oxygenated water. Major Baltic Inflows decreased frequently in the early 1980s and there was a stagnation period until the early 1990s. Although the cod stock decreased due to cod recruitment decline caused by degraded environmental conditions, the fishing effort remained high. Unfavorable cod recruitment conditions and high fishing pressure caused a remarkable drop in cod biomass. As the Central Baltic Sea is characterized by simple food web with low species diversity, cod decrease allowed its' prey sprat to increase. Cod fishing further reduced the stock, making cod even more sensitive to adverse environmental conditions. International fishing quotas have been set to limit the cod fishing but they have not always been followed. The quotas have consistently been greater than the scientific recommendations.

Studies suggest that the large increase of the sprat stock has changed the system from mainly bottom-up to top-down trophic control. A trophic cascade occurred as the sprat stock dramatically increased. High sprat abundance changed the quantity and quality of zooplankton, which feeds on phytoplankton. A sub-shift in zooplankton species can be observed to have happened until the end of the 1980s: a shift in dominance occurred from Pseudocalanus spp., the main food supply for cod larvae, to the main food supply of sprat larvae and adults, Acartia spp. and Temora longicornis. Salinity, temperature, predation of sprat, herring and mysids and climate in general regulate the zooplankton species as they all have their specific abiotic preferences. Through trophic cascades large sprat stock also lead to higher phytoplankton biomass and algal blooms during summer. Algae growth promotes further anoxia. A sprat-dominated food web has been suggested to stabilize the cod stock by sprat predating on cod eggs and larvae, and through sprat competing with young cod for zooplankton resources. Changed abundance of sprat may have even been reflected to the top levels of the Baltic food web: the condition of Common Murre (Uria aalge) chicks seem to increase and decrease in relation to sprat stock. This way human exploitation combined to natural changes caused variations in several trophic levels, which altered the ecosystem functioning as the interaction between species changed.

 

Impacts on ecosystem services and human well-being

The main ecosystem services associated with the cod-dominated regime were commercially viable, high value cod stocks, recreational value of large cod stocks and a sustainable small-scale fishing sector favoring regional development. The regime was possibly related to high water quality stimulating tourism development. Cod provide the Baltic Sea region with provisioning services: Cod is commercially the most important species in the Baltic Sea for a large number of fishermen. In the sprat-dominated region, the economic value of the catch for human consumption decreases due to the relative composition of the fish species. Being a predator at the top of the food chain, cod provides the Baltic Sea with regulating ecosystem services: cod reduces sprat, which prey on zooplankton and early life stages of cod. The high summer levels of phytoplankton could partly be a result of the sprat predation-induced decrease in total zooplankton biomass. The decay of increased algae leads to oxygen deficit and thereby causes damage to the biodiversity. The regulating role of cod may also be reflected to the top levels of the Baltic food web, the sea birds. The sprat-dominated regime is dominated by low value fish used for reduction fisheries and international fish meal and fish oil markets. These large-scale fisheries are mainly based outside the Baltic Sea region, which makes the regime less advantageous for the local development. The sprat-dominated regime may be associated with cascading effects on water quality as the low biomass of summer zooplankton may increase the probability for cyanobacterial blooms.

Low cod biomass makes industrial fishing and businesses associated with recreational fishing less profitable. Increased occurrence of algal blooms makes the Baltic Sea less attractive for tourists and recreation. From the socioeconomic perspective, tourist industry is more important than fishing industry in for example Sweden. The Baltic Sea environment and its cultural fishing surroundings are important tourist attractions. The toxic blooms and low water quality are nuisance for coastal property owners, local enterprises, bathers and others seeking for creation on the coasts. 

Management options

The goal for managing the regime shift is to maintain the resilience of the Baltic Sea ecosystem by targeting eutrophication and recovery of the cod stock. The management actions to reduce nutrient pollution began in the 1970s, when Helsinki Commission (HELCOM) adopted several recommendations for all sectors (industry, agriculture, wastewater treatment). Since the 1980s, HELCOM has worked with the 50% reduction targets for nutrients and discharges. Several countries have recently agreed to substantially reduce fertilizer use in the region (Baltic Sea Action Plan). In 1990s, it became obvious that the important Baltic Sea fish stocks were in a poor state and the fisheries were not under satisfactory control. The International Baltic Sea Fishery Commission (IBSFC) reacted with several resolutions to reduce fishing mortality and improve selectivity for cod. The main initiatives were to improve control and enforcement to assure adherence to TACs, set TACs based on target fishing mortalities, introduce technical measures to improve selectivity, and seasonal closures of areas to protect the spawning stock. However, the overexploitation of cod resources continued: the scientific advice was disregarded when setting quotas and the quotas restricting exploitation were not enforced.

In 1999, a Long-Term Management Strategy for Cod Stocks in the Baltic Sea was made including e.g. efforts to maintain a minimum spawning-stock biomass. The Recovery Plan for Baltic Sea Cod was developed in 2001 requiring a.o. seasonal closures and ban on fishing on the cod spawning grounds. Still, the problems remained and in 2004 it was acknowledged that the state of the cod stock had not improved, requiring determined action based on scientific advice. The EU agreed a plan for the Baltic Sea cod in 2007. In 2009 and 2010, The European Council Regulation for the Baltic TAC involved reductions in the number of fishing days per year. The cod fisheries are regulated by a seasonal closure to protect spawning fish. A year-round area closure for all fisheries in specific parts of the Bornholm Deep, the Gotland Basin and the Gdansk Deep was introduced in 2005.

High-grading has been prohibited since 2010 in all Baltic fisheries. In 2003, the minimum landing size was raised from 35 cm to 38 cm to protect the juvenile cods, which have not had a chance to reproduce yet. Additionally, fishing nets with exit windows have been introduced. To combat illegal fishing EU Commission has made inspections on randomly selected vessels and concluded that illegal fishing is substantial and practiced by many Baltic Sea countries. 

Key References

  1. Booth, A. 2002. The Changing Role of Non-Farm Activities in Agricultural Households in Indonesia: Some Insights From the Agricultural Censuses. Bulletin of Indonesian Economic Studies 38, 179-200.
  2. Janssen MA. 2007. Coordination in irrigation systems: An analysis of the Lansing–Kremer model of Bali. Agricultural Systems 93(1-3), 170–190.
  3. Lansing JS, Kremer JN, Gerhart V, Kremer P, Arthawiguna A, Surata SKP, Suryawan SIB, Arsana G, Scarborough VL, Schoenfelder J, Mikita K. 2001. Volcanic fertilization of Balinese rice paddies. Ecological Economics 38, 383–390.
  4. Lansing JS, Miller JH. 2005. Cooperation, games, and ecological feedback: Some insights from Bali. Current Anthropology 46(2), 328–334.
  5. Lansing JS. 1987. Lansing Balinese "Water Temples" and the management of irrigation. American Anthropologist 89, 326–341.
  6. Lansing JS. 1991. Priests and programmers: Technologies of power in the engineered landscape of Bali. Princeton University Press, Princeton.
  7. Lansing, JS, Downey SS, Jannsen M, Schoenfelder J. 2009. A Robust Budding Model of Balinese Water Temple Networks. World Archaeology 41(1), 112–133.
  8. Lietaer B, Meulenaere SD. 2003. Sustaining cultural vitality in a globalizing world: the Balinese example. International Journal of Social Economics 30, 967-984.
  9. Lorenzen RP, Lorenzen S. 2010. Changing realities, perspectives on Balinese rice cultivation. Human Ecology [http://dx.doi.org/10.1007/s10745-010-9345-z]
  10. Lorenzen S, Lorenzen RP. 2008. Institutionalizing the Informal: Irrigation and government intervention in Bali. Development 51, 77-82.
  11. Marion GS, Dunbar RB, Mucciarone DA, Kremer JN, Lansing JS, Arthawiguna A. 2005. Coral skeletal delta(15)N reveals isotopic traces of an agricultural revolution. Marine pollution bulletin 50, 931-44.
  12. Pesticide action network, Asia and the Pacific (PANAP). 2010. Rice country profile for Indonesia. http:// www.panap.net/en/r/post/rice/273
  13. Poffenberger M, Zurbuchen MS. 1980. The economics of village Bali: three perspectives. Economic development and cultural change 29(1),91-133.
  14. Roche F. 1994. The Technical and Price Efficiency of Fertiliser use in Irrigated Rice Production. Bulletin of Indonesian Economic Studies 30, 59-83.
  15. Scarborough VL, Schoenfelder JW, Lansing JS. 1999. Early statecraft on Bali: the water temple complex and the decentralization of the political economy. Research in Economic Anthropology 20, 299-330.
  16. Scarborough VL, Schoenfelder JW, Lansing JS. 2000. Ancient water management and landscape transformation at Sebatu, Bali. Bulletin of the Indo-Pacific Prehistory Associaton 20, 79-92.
  17. Schmuki A. 2007. The Role of a Global Organization in Triggering Social Learning - Insights from a Case Study of a World Heritage Cultural Landscape Nomination in Bali. Governance An International Journal Of Policy And Administration.
  18. Schoenfelder JW. 2000. The co-evolution of agricultural and sociopolitical systems in Bali. IndoPacific Prehistory Association Bulletin 4, 35-46.

Citation

Caroline Schill, Ylva Ran, Daniel Ospina, Reinette (Oonsie) Biggs, -1. Balinese rice production. In: Regime Shifts Database, www.regimeshifts.org. Last revised 2017-02-07 11:26:51 GMT.
Wednesday, 23 February 2011 22:19

Tropical lowland forests (economic use), Colombia

Written by Daniel

Tropical lowland forests (economic use), Colombia

Main Contributors:

Daniel Ospina

Other Contributors:

-1

Summary

This case is a ‘natural resource-use system’ of afro-descendant communities living in a collectively-own tropical forest territory, in the Chocó biogeographic region. This system flipped from a regime characterized by a diversified use of ecosystems, oriented mainly to subsistence and based on cooperative institutions (regime 1), to one centred on timber extraction, oriented mainly to the market and based of remunerated labour (regime 2). Regime 1 was in place for more than two centuries, not just for that population, but for virtually all the afrodescendant groups in de Colombian and Ecuadorian Pacific coast. However, in the last decades a change in the way these communities relate with the environment, as a result from the interventions from the State and big companies, has been documented. In this particular case, the shift seems to have occurred around the 1970s, after a series of biophysical and economic shocks that affected an already stressed system. One key driver was population growth, while two proposed external drivers of change were 1) the many social and production programmes designed by the national government that portrayed the local ways as inefficient and tried to replace them; and 2) the presence of big timber companies influencing a change in way ‘labour’ was viewed. The main feedback loop locking the system in this new regime is the one that links ‘timber extraction’, monetary income’ and ‘satisfaction of basic needs and desires’, and that now dominates over the one that links ‘agriculture’, ‘goods’ and ‘satisfaction of basic needs and desires’. This is further amplified by the almost complete disappearance of cooperative forms of labour, that where replaced by remunerated ones. The impact on the ecosystem is an increasing rate of timber extraction, and related with this, a change in the edapho-hydric conditions, that could in time lead to a change in the composition of these forests. Human well-being has been affected negatively as the current situation is of high dependence on timber prices and reduced food autonomy.

Type of regime shift

  • socio-economic

Ecosystem type

  • Marine & coastal
  • Tropical Forests

Land uses

  • Timber production

Spatial scale of the case study

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

Continent or Ocean

  • South America

Region

  • Chocó biogeographic region

Countries

  • Colombia

Locate with Google Map

Alternate regimes

The cod-dominated regime

The cod-dominated regime was characterized by abundant cod stocks, not only in the southern part of the Baltic Sea, but also further north and closer to shore. Cod predation regulated the number of sprat and herring. Pseudocalanus spp. dominated the zooplankton community. This regime was observed primarily during the early- to mid-1980s. 

Sprat-dominated regime

The sprat-dominated regime came into effect in 1989. A lower cod stock, an increased number of sprat and favorable conditions for sprat recruitment characterize the regime. In zooplankton community, Acartia spp. and Temora longicornis are more abundant than Psedocalanus spp. It is suggested that sprat's high predation on zooplankton lead to algal growth and declining oxygen content in deep waters. The high fishing pressure on cod is preventing the recovery of the stock and allowing the sprat to control the zooplankton. 

Drivers and causes of the regime shift

The key drivers for the Central Baltic cod-dominated regime to shift to a sprat-dominated regime are suggested to be poor cod recruitment conditions and too high fishing pressure caused by eutrophication, altered deep water conditions, infrequent inflows of North Sea saline waters and international fishing policies.

Climate functions as an indirect driver through changes in the physical environment and altered food supply for early stages. Decreased salinity, increased temperature and high sprat-predation pressure might have caused the regime subshift from Pseudocalanus spp. to Acartia spp. and Temora longicornis. Low salinity and oxygen conditions decrease the amount of the main prey of cod larvae. Higher temperatures support sprat recruitment by improving egg survival and food supply as Acartia spp. and Temora longicornis increase. 

How the regime shift worked

Cod is the main predator of sprat. It has been suggested that the large cod stock was able to control the sprat stock in the cod-dominated regime. Anthropogenic eutrophication and infrequent inflows of saline water from the North Sea contributed to increased anoxia and lowered salinity in the Central Baltic. Due to low salinity and oxygen content in the spawning areas, cod reproduction rates have remained low since the early 1980s. Deep water anoxia is a chronic stress for the survival of the cod eggs. Baltic cod needs salinity for the eggs to float in the water. If the required salinity is in anoxic conditions, eggs die.

Anoxia is one of the effects of the Baltic Sea eutrophication, but it can be temporarily reduced by inflows of North Sea saline waters, which replenish the deep-water layers of the Baltic Sea with saline and well-oxygenated water. Major Baltic Inflows decreased frequently in the early 1980s and there was a stagnation period until the early 1990s. Although the cod stock decreased due to cod recruitment decline caused by degraded environmental conditions, the fishing effort remained high. Unfavorable cod recruitment conditions and high fishing pressure caused a remarkable drop in cod biomass. As the Central Baltic Sea is characterized by simple food web with low species diversity, cod decrease allowed its' prey sprat to increase. Cod fishing further reduced the stock, making cod even more sensitive to adverse environmental conditions. International fishing quotas have been set to limit the cod fishing but they have not always been followed. The quotas have consistently been greater than the scientific recommendations.

Studies suggest that the large increase of the sprat stock has changed the system from mainly bottom-up to top-down trophic control. A trophic cascade occurred as the sprat stock dramatically increased. High sprat abundance changed the quantity and quality of zooplankton, which feeds on phytoplankton. A sub-shift in zooplankton species can be observed to have happened until the end of the 1980s: a shift in dominance occurred from Pseudocalanus spp., the main food supply for cod larvae, to the main food supply of sprat larvae and adults, Acartia spp. and Temora longicornis. Salinity, temperature, predation of sprat, herring and mysids and climate in general regulate the zooplankton species as they all have their specific abiotic preferences. Through trophic cascades large sprat stock also lead to higher phytoplankton biomass and algal blooms during summer. Algae growth promotes further anoxia. A sprat-dominated food web has been suggested to stabilize the cod stock by sprat predating on cod eggs and larvae, and through sprat competing with young cod for zooplankton resources. Changed abundance of sprat may have even been reflected to the top levels of the Baltic food web: the condition of Common Murre (Uria aalge) chicks seem to increase and decrease in relation to sprat stock. This way human exploitation combined to natural changes caused variations in several trophic levels, which altered the ecosystem functioning as the interaction between species changed.

 

Impacts on ecosystem services and human well-being

The main ecosystem services associated with the cod-dominated regime were commercially viable, high value cod stocks, recreational value of large cod stocks and a sustainable small-scale fishing sector favoring regional development. The regime was possibly related to high water quality stimulating tourism development. Cod provide the Baltic Sea region with provisioning services: Cod is commercially the most important species in the Baltic Sea for a large number of fishermen. In the sprat-dominated region, the economic value of the catch for human consumption decreases due to the relative composition of the fish species. Being a predator at the top of the food chain, cod provides the Baltic Sea with regulating ecosystem services: cod reduces sprat, which prey on zooplankton and early life stages of cod. The high summer levels of phytoplankton could partly be a result of the sprat predation-induced decrease in total zooplankton biomass. The decay of increased algae leads to oxygen deficit and thereby causes damage to the biodiversity. The regulating role of cod may also be reflected to the top levels of the Baltic food web, the sea birds. The sprat-dominated regime is dominated by low value fish used for reduction fisheries and international fish meal and fish oil markets. These large-scale fisheries are mainly based outside the Baltic Sea region, which makes the regime less advantageous for the local development. The sprat-dominated regime may be associated with cascading effects on water quality as the low biomass of summer zooplankton may increase the probability for cyanobacterial blooms.

Low cod biomass makes industrial fishing and businesses associated with recreational fishing less profitable. Increased occurrence of algal blooms makes the Baltic Sea less attractive for tourists and recreation. From the socioeconomic perspective, tourist industry is more important than fishing industry in for example Sweden. The Baltic Sea environment and its cultural fishing surroundings are important tourist attractions. The toxic blooms and low water quality are nuisance for coastal property owners, local enterprises, bathers and others seeking for creation on the coasts. 

Management options

The goal for managing the regime shift is to maintain the resilience of the Baltic Sea ecosystem by targeting eutrophication and recovery of the cod stock. The management actions to reduce nutrient pollution began in the 1970s, when Helsinki Commission (HELCOM) adopted several recommendations for all sectors (industry, agriculture, wastewater treatment). Since the 1980s, HELCOM has worked with the 50% reduction targets for nutrients and discharges. Several countries have recently agreed to substantially reduce fertilizer use in the region (Baltic Sea Action Plan). In 1990s, it became obvious that the important Baltic Sea fish stocks were in a poor state and the fisheries were not under satisfactory control. The International Baltic Sea Fishery Commission (IBSFC) reacted with several resolutions to reduce fishing mortality and improve selectivity for cod. The main initiatives were to improve control and enforcement to assure adherence to TACs, set TACs based on target fishing mortalities, introduce technical measures to improve selectivity, and seasonal closures of areas to protect the spawning stock. However, the overexploitation of cod resources continued: the scientific advice was disregarded when setting quotas and the quotas restricting exploitation were not enforced.

In 1999, a Long-Term Management Strategy for Cod Stocks in the Baltic Sea was made including e.g. efforts to maintain a minimum spawning-stock biomass. The Recovery Plan for Baltic Sea Cod was developed in 2001 requiring a.o. seasonal closures and ban on fishing on the cod spawning grounds. Still, the problems remained and in 2004 it was acknowledged that the state of the cod stock had not improved, requiring determined action based on scientific advice. The EU agreed a plan for the Baltic Sea cod in 2007. In 2009 and 2010, The European Council Regulation for the Baltic TAC involved reductions in the number of fishing days per year. The cod fisheries are regulated by a seasonal closure to protect spawning fish. A year-round area closure for all fisheries in specific parts of the Bornholm Deep, the Gotland Basin and the Gdansk Deep was introduced in 2005.

High-grading has been prohibited since 2010 in all Baltic fisheries. In 2003, the minimum landing size was raised from 35 cm to 38 cm to protect the juvenile cods, which have not had a chance to reproduce yet. Additionally, fishing nets with exit windows have been introduced. To combat illegal fishing EU Commission has made inspections on randomly selected vessels and concluded that illegal fishing is substantial and practiced by many Baltic Sea countries. 

Alternate regimes

The cod-dominated regime

The cod-dominated regime was characterized by abundant cod stocks, not only in the southern part of the Baltic Sea, but also further north and closer to shore. Cod predation regulated the number of sprat and herring. Pseudocalanus spp. dominated the zooplankton community. This regime was observed primarily during the early- to mid-1980s. 

Sprat-dominated regime

The sprat-dominated regime came into effect in 1989. A lower cod stock, an increased number of sprat and favorable conditions for sprat recruitment characterize the regime. In zooplankton community, Acartia spp. and Temora longicornis are more abundant than Psedocalanus spp. It is suggested that sprat's high predation on zooplankton lead to algal growth and declining oxygen content in deep waters. The high fishing pressure on cod is preventing the recovery of the stock and allowing the sprat to control the zooplankton. 

Drivers and causes of the regime shift

The key drivers for the Central Baltic cod-dominated regime to shift to a sprat-dominated regime are suggested to be poor cod recruitment conditions and too high fishing pressure caused by eutrophication, altered deep water conditions, infrequent inflows of North Sea saline waters and international fishing policies.

Climate functions as an indirect driver through changes in the physical environment and altered food supply for early stages. Decreased salinity, increased temperature and high sprat-predation pressure might have caused the regime subshift from Pseudocalanus spp. to Acartia spp. and Temora longicornis. Low salinity and oxygen conditions decrease the amount of the main prey of cod larvae. Higher temperatures support sprat recruitment by improving egg survival and food supply as Acartia spp. and Temora longicornis increase. 

How the regime shift worked

Cod is the main predator of sprat. It has been suggested that the large cod stock was able to control the sprat stock in the cod-dominated regime. Anthropogenic eutrophication and infrequent inflows of saline water from the North Sea contributed to increased anoxia and lowered salinity in the Central Baltic. Due to low salinity and oxygen content in the spawning areas, cod reproduction rates have remained low since the early 1980s. Deep water anoxia is a chronic stress for the survival of the cod eggs. Baltic cod needs salinity for the eggs to float in the water. If the required salinity is in anoxic conditions, eggs die.

Anoxia is one of the effects of the Baltic Sea eutrophication, but it can be temporarily reduced by inflows of North Sea saline waters, which replenish the deep-water layers of the Baltic Sea with saline and well-oxygenated water. Major Baltic Inflows decreased frequently in the early 1980s and there was a stagnation period until the early 1990s. Although the cod stock decreased due to cod recruitment decline caused by degraded environmental conditions, the fishing effort remained high. Unfavorable cod recruitment conditions and high fishing pressure caused a remarkable drop in cod biomass. As the Central Baltic Sea is characterized by simple food web with low species diversity, cod decrease allowed its' prey sprat to increase. Cod fishing further reduced the stock, making cod even more sensitive to adverse environmental conditions. International fishing quotas have been set to limit the cod fishing but they have not always been followed. The quotas have consistently been greater than the scientific recommendations.

Studies suggest that the large increase of the sprat stock has changed the system from mainly bottom-up to top-down trophic control. A trophic cascade occurred as the sprat stock dramatically increased. High sprat abundance changed the quantity and quality of zooplankton, which feeds on phytoplankton. A sub-shift in zooplankton species can be observed to have happened until the end of the 1980s: a shift in dominance occurred from Pseudocalanus spp., the main food supply for cod larvae, to the main food supply of sprat larvae and adults, Acartia spp. and Temora longicornis. Salinity, temperature, predation of sprat, herring and mysids and climate in general regulate the zooplankton species as they all have their specific abiotic preferences. Through trophic cascades large sprat stock also lead to higher phytoplankton biomass and algal blooms during summer. Algae growth promotes further anoxia. A sprat-dominated food web has been suggested to stabilize the cod stock by sprat predating on cod eggs and larvae, and through sprat competing with young cod for zooplankton resources. Changed abundance of sprat may have even been reflected to the top levels of the Baltic food web: the condition of Common Murre (Uria aalge) chicks seem to increase and decrease in relation to sprat stock. This way human exploitation combined to natural changes caused variations in several trophic levels, which altered the ecosystem functioning as the interaction between species changed.

 

Impacts on ecosystem services and human well-being

The main ecosystem services associated with the cod-dominated regime were commercially viable, high value cod stocks, recreational value of large cod stocks and a sustainable small-scale fishing sector favoring regional development. The regime was possibly related to high water quality stimulating tourism development. Cod provide the Baltic Sea region with provisioning services: Cod is commercially the most important species in the Baltic Sea for a large number of fishermen. In the sprat-dominated region, the economic value of the catch for human consumption decreases due to the relative composition of the fish species. Being a predator at the top of the food chain, cod provides the Baltic Sea with regulating ecosystem services: cod reduces sprat, which prey on zooplankton and early life stages of cod. The high summer levels of phytoplankton could partly be a result of the sprat predation-induced decrease in total zooplankton biomass. The decay of increased algae leads to oxygen deficit and thereby causes damage to the biodiversity. The regulating role of cod may also be reflected to the top levels of the Baltic food web, the sea birds. The sprat-dominated regime is dominated by low value fish used for reduction fisheries and international fish meal and fish oil markets. These large-scale fisheries are mainly based outside the Baltic Sea region, which makes the regime less advantageous for the local development. The sprat-dominated regime may be associated with cascading effects on water quality as the low biomass of summer zooplankton may increase the probability for cyanobacterial blooms.

Low cod biomass makes industrial fishing and businesses associated with recreational fishing less profitable. Increased occurrence of algal blooms makes the Baltic Sea less attractive for tourists and recreation. From the socioeconomic perspective, tourist industry is more important than fishing industry in for example Sweden. The Baltic Sea environment and its cultural fishing surroundings are important tourist attractions. The toxic blooms and low water quality are nuisance for coastal property owners, local enterprises, bathers and others seeking for creation on the coasts. 

Management options

The goal for managing the regime shift is to maintain the resilience of the Baltic Sea ecosystem by targeting eutrophication and recovery of the cod stock. The management actions to reduce nutrient pollution began in the 1970s, when Helsinki Commission (HELCOM) adopted several recommendations for all sectors (industry, agriculture, wastewater treatment). Since the 1980s, HELCOM has worked with the 50% reduction targets for nutrients and discharges. Several countries have recently agreed to substantially reduce fertilizer use in the region (Baltic Sea Action Plan). In 1990s, it became obvious that the important Baltic Sea fish stocks were in a poor state and the fisheries were not under satisfactory control. The International Baltic Sea Fishery Commission (IBSFC) reacted with several resolutions to reduce fishing mortality and improve selectivity for cod. The main initiatives were to improve control and enforcement to assure adherence to TACs, set TACs based on target fishing mortalities, introduce technical measures to improve selectivity, and seasonal closures of areas to protect the spawning stock. However, the overexploitation of cod resources continued: the scientific advice was disregarded when setting quotas and the quotas restricting exploitation were not enforced.

In 1999, a Long-Term Management Strategy for Cod Stocks in the Baltic Sea was made including e.g. efforts to maintain a minimum spawning-stock biomass. The Recovery Plan for Baltic Sea Cod was developed in 2001 requiring a.o. seasonal closures and ban on fishing on the cod spawning grounds. Still, the problems remained and in 2004 it was acknowledged that the state of the cod stock had not improved, requiring determined action based on scientific advice. The EU agreed a plan for the Baltic Sea cod in 2007. In 2009 and 2010, The European Council Regulation for the Baltic TAC involved reductions in the number of fishing days per year. The cod fisheries are regulated by a seasonal closure to protect spawning fish. A year-round area closure for all fisheries in specific parts of the Bornholm Deep, the Gotland Basin and the Gdansk Deep was introduced in 2005.

High-grading has been prohibited since 2010 in all Baltic fisheries. In 2003, the minimum landing size was raised from 35 cm to 38 cm to protect the juvenile cods, which have not had a chance to reproduce yet. Additionally, fishing nets with exit windows have been introduced. To combat illegal fishing EU Commission has made inspections on randomly selected vessels and concluded that illegal fishing is substantial and practiced by many Baltic Sea countries. 

Key References

  1. Del Valle JI & Restrepo E. (eds) 1996. Renacientes del guandal. “grupos negros” de los ríos Satinga y Sanquianga. UN–PBP, Bogotá DC.
  2. Escobar A & Pedrosa A. (eds) 1996. Pacífico ¿desarrollo o diversidad? Estado, capital y movimientos sociales en el Pacífico colombiano. CEREC-Ecofondo, Bogotá DC.
  3. Leal C & Restrepo E. 2003. Unos bosques sembrados de aserríos: historia de la extracción maderera en el Pacífico colombiano. ICANH–UN–Universidad de Antioquia, Medellín.
  4. Proyecto Biopacífico. 1994. Economías de las comunidades rurales en el Pacífico colombiano (Memorias del foro Las economías rurales indígenas, negras y mestizas en el Pacífico colombiano, Sena-Codechoco-PBP, Octubre 19-21 de 1994, Quibdó). MMA-PNUD-GEF, Bogotá DC.
  5. West RC. 1957. The Pacific lowlands of Colombia: A negroid area of the American tropics. Louisiana State University Press, Baton Rough.
  6. Whitten NE Jr. 1986. Black Frontiersmen: Afro-Hispanic Culture of Ecuador and Colombia. Waveland Press, Prospect Heights.

Citation

Daniel Ospina, -1. Tropical lowland forests (economic use), Colombia. In: Regime Shifts Database, www.regimeshifts.org. Last revised 2013-08-25 21:53:08 GMT.
Tuesday, 15 February 2011 11:54

Maradi Agro-ecosystem

Written by Reinette (Oonsie) Biggs

Maradi Agro-ecosystem

Main Contributors:

Johnny Musumbu Tshimpanga

Other Contributors:

Garry Peterson, Reinette (Oonsie) Biggs, Elin Enfors

Summary

Niger’s landscapes in general, particularly in Maradi have undergone a regime shift from a highly productive to a desert-dominated regime. The productive regime was maintained by land use characterized by scattered rural populations cultivating small fields amidst surrounding bush. Yields were sufficient and there were abundant supplies of forest products made possible by wet climatic conditions. The implementation of a new land law established the national government as the owner of all trees and provided disincentives for farmers to care for their land. This led to the exposure of soils to the Sahara winds resulting in erosion and accelerating desertification. This resulted in hunger and destitute among many people. Key institutional changes with regards to land tenure and tree growth were put in place along with simple soil and water conservation techniques, rock lining, improved versions of traditional planting pits or tasa, and demi-lunes which have reversed desertification. This process has reduced erosion and increased fertility and crop production, income, food security, and self-reliance to impoverished rural producers.

Type of regime shift

  • Desertification

Ecosystem type

  • Drylands & deserts (below ~500mm rainfall/year)

Land uses

  • Small-scale subsistence crop cultivation
  • Extensive livestock production (natural rangelands)

Spatial scale of the case study

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

Continent or Ocean

  • Africa

Region

  • Sahel

Countries

  • Niger

Locate with Google Map

Drivers

Key direct drivers

  • Harvest and resource consumption
  • External inputs (eg fertilizers)
  • Species introduction or removal

Impacts

Ecosystem type

  • Marine & coastal

Key Ecosystem Processes

  • Nutrient cycling
  • Water cycling

Biodiversity

  • Biodiversity

Provisioning services

  • Fisheries

Regulating services

  • Water purification

Cultural services

  • Recreation
  • Aesthetic values

Human Well-being

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

Key Attributes

Spatial scale of RS

  • Sub-continental/regional

Time scale of RS

  • Years
  • Decades

Reversibility

  • Unknown

Evidence

  • Models
  • Contemporary observations
  • Experiments

Confidence: Existence of RS

  • Contested – Reasonable evidence both for and against the existence of RS

Confidence: Mechanism underlying RS

  • Contested – Multiple proposed mechanisms, reasonable evidence both for and against different mechanisms

Alternate regimes

The cod-dominated regime

The cod-dominated regime was characterized by abundant cod stocks, not only in the southern part of the Baltic Sea, but also further north and closer to shore. Cod predation regulated the number of sprat and herring. Pseudocalanus spp. dominated the zooplankton community. This regime was observed primarily during the early- to mid-1980s. 

Sprat-dominated regime

The sprat-dominated regime came into effect in 1989. A lower cod stock, an increased number of sprat and favorable conditions for sprat recruitment characterize the regime. In zooplankton community, Acartia spp. and Temora longicornis are more abundant than Psedocalanus spp. It is suggested that sprat's high predation on zooplankton lead to algal growth and declining oxygen content in deep waters. The high fishing pressure on cod is preventing the recovery of the stock and allowing the sprat to control the zooplankton. 

Drivers and causes of the regime shift

The key drivers for the Central Baltic cod-dominated regime to shift to a sprat-dominated regime are suggested to be poor cod recruitment conditions and too high fishing pressure caused by eutrophication, altered deep water conditions, infrequent inflows of North Sea saline waters and international fishing policies.

Climate functions as an indirect driver through changes in the physical environment and altered food supply for early stages. Decreased salinity, increased temperature and high sprat-predation pressure might have caused the regime subshift from Pseudocalanus spp. to Acartia spp. and Temora longicornis. Low salinity and oxygen conditions decrease the amount of the main prey of cod larvae. Higher temperatures support sprat recruitment by improving egg survival and food supply as Acartia spp. and Temora longicornis increase. 

How the regime shift worked

Cod is the main predator of sprat. It has been suggested that the large cod stock was able to control the sprat stock in the cod-dominated regime. Anthropogenic eutrophication and infrequent inflows of saline water from the North Sea contributed to increased anoxia and lowered salinity in the Central Baltic. Due to low salinity and oxygen content in the spawning areas, cod reproduction rates have remained low since the early 1980s. Deep water anoxia is a chronic stress for the survival of the cod eggs. Baltic cod needs salinity for the eggs to float in the water. If the required salinity is in anoxic conditions, eggs die.

Anoxia is one of the effects of the Baltic Sea eutrophication, but it can be temporarily reduced by inflows of North Sea saline waters, which replenish the deep-water layers of the Baltic Sea with saline and well-oxygenated water. Major Baltic Inflows decreased frequently in the early 1980s and there was a stagnation period until the early 1990s. Although the cod stock decreased due to cod recruitment decline caused by degraded environmental conditions, the fishing effort remained high. Unfavorable cod recruitment conditions and high fishing pressure caused a remarkable drop in cod biomass. As the Central Baltic Sea is characterized by simple food web with low species diversity, cod decrease allowed its' prey sprat to increase. Cod fishing further reduced the stock, making cod even more sensitive to adverse environmental conditions. International fishing quotas have been set to limit the cod fishing but they have not always been followed. The quotas have consistently been greater than the scientific recommendations.

Studies suggest that the large increase of the sprat stock has changed the system from mainly bottom-up to top-down trophic control. A trophic cascade occurred as the sprat stock dramatically increased. High sprat abundance changed the quantity and quality of zooplankton, which feeds on phytoplankton. A sub-shift in zooplankton species can be observed to have happened until the end of the 1980s: a shift in dominance occurred from Pseudocalanus spp., the main food supply for cod larvae, to the main food supply of sprat larvae and adults, Acartia spp. and Temora longicornis. Salinity, temperature, predation of sprat, herring and mysids and climate in general regulate the zooplankton species as they all have their specific abiotic preferences. Through trophic cascades large sprat stock also lead to higher phytoplankton biomass and algal blooms during summer. Algae growth promotes further anoxia. A sprat-dominated food web has been suggested to stabilize the cod stock by sprat predating on cod eggs and larvae, and through sprat competing with young cod for zooplankton resources. Changed abundance of sprat may have even been reflected to the top levels of the Baltic food web: the condition of Common Murre (Uria aalge) chicks seem to increase and decrease in relation to sprat stock. This way human exploitation combined to natural changes caused variations in several trophic levels, which altered the ecosystem functioning as the interaction between species changed.

 

Impacts on ecosystem services and human well-being

The main ecosystem services associated with the cod-dominated regime were commercially viable, high value cod stocks, recreational value of large cod stocks and a sustainable small-scale fishing sector favoring regional development. The regime was possibly related to high water quality stimulating tourism development. Cod provide the Baltic Sea region with provisioning services: Cod is commercially the most important species in the Baltic Sea for a large number of fishermen. In the sprat-dominated region, the economic value of the catch for human consumption decreases due to the relative composition of the fish species. Being a predator at the top of the food chain, cod provides the Baltic Sea with regulating ecosystem services: cod reduces sprat, which prey on zooplankton and early life stages of cod. The high summer levels of phytoplankton could partly be a result of the sprat predation-induced decrease in total zooplankton biomass. The decay of increased algae leads to oxygen deficit and thereby causes damage to the biodiversity. The regulating role of cod may also be reflected to the top levels of the Baltic food web, the sea birds. The sprat-dominated regime is dominated by low value fish used for reduction fisheries and international fish meal and fish oil markets. These large-scale fisheries are mainly based outside the Baltic Sea region, which makes the regime less advantageous for the local development. The sprat-dominated regime may be associated with cascading effects on water quality as the low biomass of summer zooplankton may increase the probability for cyanobacterial blooms.

Low cod biomass makes industrial fishing and businesses associated with recreational fishing less profitable. Increased occurrence of algal blooms makes the Baltic Sea less attractive for tourists and recreation. From the socioeconomic perspective, tourist industry is more important than fishing industry in for example Sweden. The Baltic Sea environment and its cultural fishing surroundings are important tourist attractions. The toxic blooms and low water quality are nuisance for coastal property owners, local enterprises, bathers and others seeking for creation on the coasts. 

Management options

The goal for managing the regime shift is to maintain the resilience of the Baltic Sea ecosystem by targeting eutrophication and recovery of the cod stock. The management actions to reduce nutrient pollution began in the 1970s, when Helsinki Commission (HELCOM) adopted several recommendations for all sectors (industry, agriculture, wastewater treatment). Since the 1980s, HELCOM has worked with the 50% reduction targets for nutrients and discharges. Several countries have recently agreed to substantially reduce fertilizer use in the region (Baltic Sea Action Plan). In 1990s, it became obvious that the important Baltic Sea fish stocks were in a poor state and the fisheries were not under satisfactory control. The International Baltic Sea Fishery Commission (IBSFC) reacted with several resolutions to reduce fishing mortality and improve selectivity for cod. The main initiatives were to improve control and enforcement to assure adherence to TACs, set TACs based on target fishing mortalities, introduce technical measures to improve selectivity, and seasonal closures of areas to protect the spawning stock. However, the overexploitation of cod resources continued: the scientific advice was disregarded when setting quotas and the quotas restricting exploitation were not enforced.

In 1999, a Long-Term Management Strategy for Cod Stocks in the Baltic Sea was made including e.g. efforts to maintain a minimum spawning-stock biomass. The Recovery Plan for Baltic Sea Cod was developed in 2001 requiring a.o. seasonal closures and ban on fishing on the cod spawning grounds. Still, the problems remained and in 2004 it was acknowledged that the state of the cod stock had not improved, requiring determined action based on scientific advice. The EU agreed a plan for the Baltic Sea cod in 2007. In 2009 and 2010, The European Council Regulation for the Baltic TAC involved reductions in the number of fishing days per year. The cod fisheries are regulated by a seasonal closure to protect spawning fish. A year-round area closure for all fisheries in specific parts of the Bornholm Deep, the Gotland Basin and the Gdansk Deep was introduced in 2005.

High-grading has been prohibited since 2010 in all Baltic fisheries. In 2003, the minimum landing size was raised from 35 cm to 38 cm to protect the juvenile cods, which have not had a chance to reproduce yet. Additionally, fishing nets with exit windows have been introduced. To combat illegal fishing EU Commission has made inspections on randomly selected vessels and concluded that illegal fishing is substantial and practiced by many Baltic Sea countries. 

Alternate regimes

The cod-dominated regime

The cod-dominated regime was characterized by abundant cod stocks, not only in the southern part of the Baltic Sea, but also further north and closer to shore. Cod predation regulated the number of sprat and herring. Pseudocalanus spp. dominated the zooplankton community. This regime was observed primarily during the early- to mid-1980s. 

Sprat-dominated regime

The sprat-dominated regime came into effect in 1989. A lower cod stock, an increased number of sprat and favorable conditions for sprat recruitment characterize the regime. In zooplankton community, Acartia spp. and Temora longicornis are more abundant than Psedocalanus spp. It is suggested that sprat's high predation on zooplankton lead to algal growth and declining oxygen content in deep waters. The high fishing pressure on cod is preventing the recovery of the stock and allowing the sprat to control the zooplankton. 

Drivers and causes of the regime shift

The key drivers for the Central Baltic cod-dominated regime to shift to a sprat-dominated regime are suggested to be poor cod recruitment conditions and too high fishing pressure caused by eutrophication, altered deep water conditions, infrequent inflows of North Sea saline waters and international fishing policies.

Climate functions as an indirect driver through changes in the physical environment and altered food supply for early stages. Decreased salinity, increased temperature and high sprat-predation pressure might have caused the regime subshift from Pseudocalanus spp. to Acartia spp. and Temora longicornis. Low salinity and oxygen conditions decrease the amount of the main prey of cod larvae. Higher temperatures support sprat recruitment by improving egg survival and food supply as Acartia spp. and Temora longicornis increase. 

How the regime shift worked

Cod is the main predator of sprat. It has been suggested that the large cod stock was able to control the sprat stock in the cod-dominated regime. Anthropogenic eutrophication and infrequent inflows of saline water from the North Sea contributed to increased anoxia and lowered salinity in the Central Baltic. Due to low salinity and oxygen content in the spawning areas, cod reproduction rates have remained low since the early 1980s. Deep water anoxia is a chronic stress for the survival of the cod eggs. Baltic cod needs salinity for the eggs to float in the water. If the required salinity is in anoxic conditions, eggs die.

Anoxia is one of the effects of the Baltic Sea eutrophication, but it can be temporarily reduced by inflows of North Sea saline waters, which replenish the deep-water layers of the Baltic Sea with saline and well-oxygenated water. Major Baltic Inflows decreased frequently in the early 1980s and there was a stagnation period until the early 1990s. Although the cod stock decreased due to cod recruitment decline caused by degraded environmental conditions, the fishing effort remained high. Unfavorable cod recruitment conditions and high fishing pressure caused a remarkable drop in cod biomass. As the Central Baltic Sea is characterized by simple food web with low species diversity, cod decrease allowed its' prey sprat to increase. Cod fishing further reduced the stock, making cod even more sensitive to adverse environmental conditions. International fishing quotas have been set to limit the cod fishing but they have not always been followed. The quotas have consistently been greater than the scientific recommendations.

Studies suggest that the large increase of the sprat stock has changed the system from mainly bottom-up to top-down trophic control. A trophic cascade occurred as the sprat stock dramatically increased. High sprat abundance changed the quantity and quality of zooplankton, which feeds on phytoplankton. A sub-shift in zooplankton species can be observed to have happened until the end of the 1980s: a shift in dominance occurred from Pseudocalanus spp., the main food supply for cod larvae, to the main food supply of sprat larvae and adults, Acartia spp. and Temora longicornis. Salinity, temperature, predation of sprat, herring and mysids and climate in general regulate the zooplankton species as they all have their specific abiotic preferences. Through trophic cascades large sprat stock also lead to higher phytoplankton biomass and algal blooms during summer. Algae growth promotes further anoxia. A sprat-dominated food web has been suggested to stabilize the cod stock by sprat predating on cod eggs and larvae, and through sprat competing with young cod for zooplankton resources. Changed abundance of sprat may have even been reflected to the top levels of the Baltic food web: the condition of Common Murre (Uria aalge) chicks seem to increase and decrease in relation to sprat stock. This way human exploitation combined to natural changes caused variations in several trophic levels, which altered the ecosystem functioning as the interaction between species changed.

 

Impacts on ecosystem services and human well-being

The main ecosystem services associated with the cod-dominated regime were commercially viable, high value cod stocks, recreational value of large cod stocks and a sustainable small-scale fishing sector favoring regional development. The regime was possibly related to high water quality stimulating tourism development. Cod provide the Baltic Sea region with provisioning services: Cod is commercially the most important species in the Baltic Sea for a large number of fishermen. In the sprat-dominated region, the economic value of the catch for human consumption decreases due to the relative composition of the fish species. Being a predator at the top of the food chain, cod provides the Baltic Sea with regulating ecosystem services: cod reduces sprat, which prey on zooplankton and early life stages of cod. The high summer levels of phytoplankton could partly be a result of the sprat predation-induced decrease in total zooplankton biomass. The decay of increased algae leads to oxygen deficit and thereby causes damage to the biodiversity. The regulating role of cod may also be reflected to the top levels of the Baltic food web, the sea birds. The sprat-dominated regime is dominated by low value fish used for reduction fisheries and international fish meal and fish oil markets. These large-scale fisheries are mainly based outside the Baltic Sea region, which makes the regime less advantageous for the local development. The sprat-dominated regime may be associated with cascading effects on water quality as the low biomass of summer zooplankton may increase the probability for cyanobacterial blooms.

Low cod biomass makes industrial fishing and businesses associated with recreational fishing less profitable. Increased occurrence of algal blooms makes the Baltic Sea less attractive for tourists and recreation. From the socioeconomic perspective, tourist industry is more important than fishing industry in for example Sweden. The Baltic Sea environment and its cultural fishing surroundings are important tourist attractions. The toxic blooms and low water quality are nuisance for coastal property owners, local enterprises, bathers and others seeking for creation on the coasts. 

Management options

The goal for managing the regime shift is to maintain the resilience of the Baltic Sea ecosystem by targeting eutrophication and recovery of the cod stock. The management actions to reduce nutrient pollution began in the 1970s, when Helsinki Commission (HELCOM) adopted several recommendations for all sectors (industry, agriculture, wastewater treatment). Since the 1980s, HELCOM has worked with the 50% reduction targets for nutrients and discharges. Several countries have recently agreed to substantially reduce fertilizer use in the region (Baltic Sea Action Plan). In 1990s, it became obvious that the important Baltic Sea fish stocks were in a poor state and the fisheries were not under satisfactory control. The International Baltic Sea Fishery Commission (IBSFC) reacted with several resolutions to reduce fishing mortality and improve selectivity for cod. The main initiatives were to improve control and enforcement to assure adherence to TACs, set TACs based on target fishing mortalities, introduce technical measures to improve selectivity, and seasonal closures of areas to protect the spawning stock. However, the overexploitation of cod resources continued: the scientific advice was disregarded when setting quotas and the quotas restricting exploitation were not enforced.

In 1999, a Long-Term Management Strategy for Cod Stocks in the Baltic Sea was made including e.g. efforts to maintain a minimum spawning-stock biomass. The Recovery Plan for Baltic Sea Cod was developed in 2001 requiring a.o. seasonal closures and ban on fishing on the cod spawning grounds. Still, the problems remained and in 2004 it was acknowledged that the state of the cod stock had not improved, requiring determined action based on scientific advice. The EU agreed a plan for the Baltic Sea cod in 2007. In 2009 and 2010, The European Council Regulation for the Baltic TAC involved reductions in the number of fishing days per year. The cod fisheries are regulated by a seasonal closure to protect spawning fish. A year-round area closure for all fisheries in specific parts of the Bornholm Deep, the Gotland Basin and the Gdansk Deep was introduced in 2005.

High-grading has been prohibited since 2010 in all Baltic fisheries. In 2003, the minimum landing size was raised from 35 cm to 38 cm to protect the juvenile cods, which have not had a chance to reproduce yet. Additionally, fishing nets with exit windows have been introduced. To combat illegal fishing EU Commission has made inspections on randomly selected vessels and concluded that illegal fishing is substantial and practiced by many Baltic Sea countries. 

Alternate regimes

The cod-dominated regime

The cod-dominated regime was characterized by abundant cod stocks, not only in the southern part of the Baltic Sea, but also further north and closer to shore. Cod predation regulated the number of sprat and herring. Pseudocalanus spp. dominated the zooplankton community. This regime was observed primarily during the early- to mid-1980s. 

Sprat-dominated regime

The sprat-dominated regime came into effect in 1989. A lower cod stock, an increased number of sprat and favorable conditions for sprat recruitment characterize the regime. In zooplankton community, Acartia spp. and Temora longicornis are more abundant than Psedocalanus spp. It is suggested that sprat's high predation on zooplankton lead to algal growth and declining oxygen content in deep waters. The high fishing pressure on cod is preventing the recovery of the stock and allowing the sprat to control the zooplankton. 

Drivers and causes of the regime shift

The key drivers for the Central Baltic cod-dominated regime to shift to a sprat-dominated regime are suggested to be poor cod recruitment conditions and too high fishing pressure caused by eutrophication, altered deep water conditions, infrequent inflows of North Sea saline waters and international fishing policies.

Climate functions as an indirect driver through changes in the physical environment and altered food supply for early stages. Decreased salinity, increased temperature and high sprat-predation pressure might have caused the regime subshift from Pseudocalanus spp. to Acartia spp. and Temora longicornis. Low salinity and oxygen conditions decrease the amount of the main prey of cod larvae. Higher temperatures support sprat recruitment by improving egg survival and food supply as Acartia spp. and Temora longicornis increase. 

How the regime shift worked

Cod is the main predator of sprat. It has been suggested that the large cod stock was able to control the sprat stock in the cod-dominated regime. Anthropogenic eutrophication and infrequent inflows of saline water from the North Sea contributed to increased anoxia and lowered salinity in the Central Baltic. Due to low salinity and oxygen content in the spawning areas, cod reproduction rates have remained low since the early 1980s. Deep water anoxia is a chronic stress for the survival of the cod eggs. Baltic cod needs salinity for the eggs to float in the water. If the required salinity is in anoxic conditions, eggs die.

Anoxia is one of the effects of the Baltic Sea eutrophication, but it can be temporarily reduced by inflows of North Sea saline waters, which replenish the deep-water layers of the Baltic Sea with saline and well-oxygenated water. Major Baltic Inflows decreased frequently in the early 1980s and there was a stagnation period until the early 1990s. Although the cod stock decreased due to cod recruitment decline caused by degraded environmental conditions, the fishing effort remained high. Unfavorable cod recruitment conditions and high fishing pressure caused a remarkable drop in cod biomass. As the Central Baltic Sea is characterized by simple food web with low species diversity, cod decrease allowed its' prey sprat to increase. Cod fishing further reduced the stock, making cod even more sensitive to adverse environmental conditions. International fishing quotas have been set to limit the cod fishing but they have not always been followed. The quotas have consistently been greater than the scientific recommendations.

Studies suggest that the large increase of the sprat stock has changed the system from mainly bottom-up to top-down trophic control. A trophic cascade occurred as the sprat stock dramatically increased. High sprat abundance changed the quantity and quality of zooplankton, which feeds on phytoplankton. A sub-shift in zooplankton species can be observed to have happened until the end of the 1980s: a shift in dominance occurred from Pseudocalanus spp., the main food supply for cod larvae, to the main food supply of sprat larvae and adults, Acartia spp. and Temora longicornis. Salinity, temperature, predation of sprat, herring and mysids and climate in general regulate the zooplankton species as they all have their specific abiotic preferences. Through trophic cascades large sprat stock also lead to higher phytoplankton biomass and algal blooms during summer. Algae growth promotes further anoxia. A sprat-dominated food web has been suggested to stabilize the cod stock by sprat predating on cod eggs and larvae, and through sprat competing with young cod for zooplankton resources. Changed abundance of sprat may have even been reflected to the top levels of the Baltic food web: the condition of Common Murre (Uria aalge) chicks seem to increase and decrease in relation to sprat stock. This way human exploitation combined to natural changes caused variations in several trophic levels, which altered the ecosystem functioning as the interaction between species changed.

 

Impacts on ecosystem services and human well-being

The main ecosystem services associated with the cod-dominated regime were commercially viable, high value cod stocks, recreational value of large cod stocks and a sustainable small-scale fishing sector favoring regional development. The regime was possibly related to high water quality stimulating tourism development. Cod provide the Baltic Sea region with provisioning services: Cod is commercially the most important species in the Baltic Sea for a large number of fishermen. In the sprat-dominated region, the economic value of the catch for human consumption decreases due to the relative composition of the fish species. Being a predator at the top of the food chain, cod provides the Baltic Sea with regulating ecosystem services: cod reduces sprat, which prey on zooplankton and early life stages of cod. The high summer levels of phytoplankton could partly be a result of the sprat predation-induced decrease in total zooplankton biomass. The decay of increased algae leads to oxygen deficit and thereby causes damage to the biodiversity. The regulating role of cod may also be reflected to the top levels of the Baltic food web, the sea birds. The sprat-dominated regime is dominated by low value fish used for reduction fisheries and international fish meal and fish oil markets. These large-scale fisheries are mainly based outside the Baltic Sea region, which makes the regime less advantageous for the local development. The sprat-dominated regime may be associated with cascading effects on water quality as the low biomass of summer zooplankton may increase the probability for cyanobacterial blooms.

Low cod biomass makes industrial fishing and businesses associated with recreational fishing less profitable. Increased occurrence of algal blooms makes the Baltic Sea less attractive for tourists and recreation. From the socioeconomic perspective, tourist industry is more important than fishing industry in for example Sweden. The Baltic Sea environment and its cultural fishing surroundings are important tourist attractions. The toxic blooms and low water quality are nuisance for coastal property owners, local enterprises, bathers and others seeking for creation on the coasts. 

Management options

The goal for managing the regime shift is to maintain the resilience of the Baltic Sea ecosystem by targeting eutrophication and recovery of the cod stock. The management actions to reduce nutrient pollution began in the 1970s, when Helsinki Commission (HELCOM) adopted several recommendations for all sectors (industry, agriculture, wastewater treatment). Since the 1980s, HELCOM has worked with the 50% reduction targets for nutrients and discharges. Several countries have recently agreed to substantially reduce fertilizer use in the region (Baltic Sea Action Plan). In 1990s, it became obvious that the important Baltic Sea fish stocks were in a poor state and the fisheries were not under satisfactory control. The International Baltic Sea Fishery Commission (IBSFC) reacted with several resolutions to reduce fishing mortality and improve selectivity for cod. The main initiatives were to improve control and enforcement to assure adherence to TACs, set TACs based on target fishing mortalities, introduce technical measures to improve selectivity, and seasonal closures of areas to protect the spawning stock. However, the overexploitation of cod resources continued: the scientific advice was disregarded when setting quotas and the quotas restricting exploitation were not enforced.

In 1999, a Long-Term Management Strategy for Cod Stocks in the Baltic Sea was made including e.g. efforts to maintain a minimum spawning-stock biomass. The Recovery Plan for Baltic Sea Cod was developed in 2001 requiring a.o. seasonal closures and ban on fishing on the cod spawning grounds. Still, the problems remained and in 2004 it was acknowledged that the state of the cod stock had not improved, requiring determined action based on scientific advice. The EU agreed a plan for the Baltic Sea cod in 2007. In 2009 and 2010, The European Council Regulation for the Baltic TAC involved reductions in the number of fishing days per year. The cod fisheries are regulated by a seasonal closure to protect spawning fish. A year-round area closure for all fisheries in specific parts of the Bornholm Deep, the Gotland Basin and the Gdansk Deep was introduced in 2005.

High-grading has been prohibited since 2010 in all Baltic fisheries. In 2003, the minimum landing size was raised from 35 cm to 38 cm to protect the juvenile cods, which have not had a chance to reproduce yet. Additionally, fishing nets with exit windows have been introduced. To combat illegal fishing EU Commission has made inspections on randomly selected vessels and concluded that illegal fishing is substantial and practiced by many Baltic Sea countries. 

Key References

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Citation

Johnny Musumbu Tshimpanga, Garry Peterson, Reinette (Oonsie) Biggs, Elin Enfors. Maradi Agro-ecosystem. In: Regime Shifts Database, www.regimeshifts.org. Last revised 2017-02-07 12:32:20 GMT.
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