Regime Shifts DataBase

Large persistent changes in ecosystem services

Cichlid dominated regime

Cichlid – phytoplankton feedback (balancing, local scale, well established): Many cichlid species are detritivorous and planktivorous and play an important role in the nutrient recycling(Goldschmidt, Witte, and Wanink 1993) of the lake, keeping it in a clear, non-eutrophied state. More of these cichlid species will result in less phytoplankton and thus prevent hypoxia.

Cichlid – Nile perch feedback (reinforcing, local scale, well-established): In a cichlid dominated regimethere is a positive feedback from cichlids feeding on Nile perch larvae and competing with the Nile perch juveniles for feed and space. Hence, in this regime the cichlids supress the Nile perch population.

Nile perch dominated regime

Nile perch – cichlid feedback (reinforcing, local scale, well-established): The cichlids are the preferred feed for Nile perch(Kaufman 1992). Thus the cichlid populations are controlled by the Nile perch when it becomes the dominant species.Algae bloom – cichlid feedback (reinforcing, local scale, well-established): There is a positive feedback between the abundance of native cichlids and algae blooms. Detritivorous and planktivorous cichlids are important for the internal recycling in the lake and thus reduce the occurrence of algae blooms (Balirwa, et al. 2003). When the algae die the oxygen is consumed in the degradation process which leads to hypoxia. This affects the cichlids negatively and only the species adaptable to the new conditions can survive. Although the Nile perch is also sensitive to hypoxic conditions (Kaufman 1992) it has been able to survive since it occupies the pelagic zone. The hypoxia forced species from the benthic zone up to the surface making them a target for the Nile perch (Hecky, et al. 1994).

Turbidity – cichlid feedback (reinforcing, regional scale, well-established): As for the algae blooms, the cichlids have an important role in internal recycling in the lake preventing eutrophication. A low number of cichlids will keep the lake turbid. The turbidity, in turn, highly affects the reproduction of cichlids(Seehausen, et al. 1997).

Nile perch – shrimp feedback (reinforcing, local scale, well-established): An important food source for Nile perch juveniles and adults in the Nile perch dominated regime is the native shrimp Caridina nilotica (Kaufman 1992). This shrimp is an opportunistic species that survives conditions that the native cichlids are not able to survive when the conditions of the lake alter from non-eutrophicated to eutrophicated (Goldschmidt, Witte, and Wanink 1993). This results in an increase of Nile perch even when the cichlids, which are the preferred feed, are gone.

Global market – demand for Nile perch (reinforcing, global scale, well-established): Although not part of the actual regime shift the global market plays an important role in maintaining the Nile perch dominated regime. The export markets are driving the exploitation of Nile perch(Matsuishi, et al. 2006) and management plans are striving for a sustainable fishing to keep this valuable source of income in the lake for future exploitation (ibid.). 

Important shocks:

Rainfall events (regional, proposed): Following heavy rainfalls during the 1960s, extensive beds of littoral vegetation, which had served as important spawning and nursery grounds for many native species, were destroyed (Kaufman 1992). These events were seized by tilapia stocks to establish themselves and compete with cichlids (Geheb 1997). This external shock to the system is likely to have contributed to the weakening of several cichlid species (Kaufman 1992).

Main external direct drivers:

Nutrient input (regional, well-established): The anthropogenic input of nutrients in Lake Victoria lead to an increase in phytoplankton productivity. For a long time the cichlids were able to offset this rise in productivity (Ibid.). However, as they came under more severe pressure, from fishing and Nile perch predation, the balancing feedback became a reinforcing one, causing hypoxia which forced many cichlid species to migrate to shallower water where they were consumed by Nile perches –further weakening the ability of the lake to cope with the eutrophication (Hecky , et al. 1994). The staggering productivity of the lake also created a turbid state negatively affected the reproduction capacity of the cichlids (Seehausen, et al. 1997).

Over-fishing (regional, well-established): From the 1950s to the 1980s, fishing in Lake Victoria shifted towards targeting smaller and smaller taxa to compensate for the overexploitation of larger fish species(Balirwa, et al. 2003). This shift put the cichlids in the centerfold of the fishing activities and severely weakened them. It has been suggested that this made it possible for the Nile perch in certain parts of the lake to break the cichlids' upper-hand in their mutually negative reinforcing feedback(Goudswaard, Witte, and Katunzi 2008).

Main external indirect drivers:

Agriculture (regional, well-established): A major reason why the anthropogenic input of nutrients into Lake Victoria increased was the expansion of agriculture(Balirwa, et al. 2003, Verschuren, et al. 2002) and run-off carrying farm fertilizers and manure.

Deforestation (regional, well-established): Deforestation was another contributor to the amplified nutrient input. The increasing demand for agricultural land, timber, firewood, and habitation resulted in extensive deforestation. This resulted in soil erosion, depositing soil particles and nutrients into the lake (Ibid.).

Population growth (regional, well-established): Between the 1950s and the 2000s the population around Lake Victoria grew from 5 million to 30 million which created a huge demand for the resources of the lake and its surroundings. This population growth is the foremost reason why the overfishing, agricultural expansion and deforestation took off (Balirwa, et al. 2003, Balirwa 2007).

Improved fishing gear (regional, well-established): New fishing technologies, such as nylon nets and outboard motors, introduced during the 1950s, enabled for the fishing to intensify (Kitchell, et al. 1997).

Slow internal system changes:

Phosphorus and nitrogen level (regional, well-established): Increased nutrient levels in Lake Victoria, due to increased nitrogen input and internal loading of phosphorous bound in sediment, reinforce eutrophication, increase population of phytoplankton, and lead to turbid and anoxic conditions.

Cichlid level (local, proposed): In some areas of the lake, the abundance of cichlids started to deteriorate as overfishing became more prevalently focused on the smaller taxa. It has been proposed that these areas experienced a threshold dynamic when the reinforcing relationship between cichlids and Nile perch changed in favor of the latter(Goudswaard, Witte, and Katunzi 2008). From this point the Nile perch was able to step-by-step take over the lake. 

A desirable state for Lake Victoria would not necessarily involve the return to the first regime but to reach a state of both high biodiversity and profitable fishing. The most important points of leverage should focus on managing and improving the lake conditions and to control the Nile perch population (Balirwa, et al. 2003).

Prevent nutrient runoff and input (local and regional scale, well-established): Improved farming methods are important to decrease the nutrient levels in the lake (Swallow 2009).Trees and other vegetation hold the soil and nutrients in place. Improved farming methods can reduce land degradation and the need for fertilizers.Knowledge is an important part of this and there are different actors working with these projects together with local communities in the lake basin, both upstream and downstream. Mentioned by Swallow (2009) is e.g. World agroforestry center and Vi Agroforestry (ibid.).

Investments in sewage treatment and restoration of wetlands would reduce the leakage of nutrients into the lake (Balirwa, et al. 2003). This should emerge from high political levels in the countries around the Lake Victoria. There should also be guidelines forcontrolling nutrient levels (Balirwa, et al. 2003).

Fishing (regional scale, proposed): Putting further pressure on the Nile perch population could provide a window of opportunity for native species to return to the system (Balirwa, et al. 2003). This would keep the Nile perch at low level and give native species a chance to re-emerge.By strictly reinforcing the control of fishing practices (Seehausen, et al. 1997a) cichlids can be protected from the fishing. A previous study bySchindler, Kitchell, and Ogutu-Ohwayo in 1998 showed that by using a minimum mesh size of 5-inches the Nile perch cannibalism and the predation of native species would be reduced by 44% at the same time as the catches of Nile perch only was reduced by 10%.

Reintroduction of cichlids (regional scale, well-established): Reintroduction of cichlid species can boost the abundance of these species and increase the biodiversity. This can be done once the conditions of the lake are somewhat restored.Seehausen, et al. (1997), suggest the construction of ponds for cichlid aquaculture to protect surrounding lakes from new species.

For all these leverage points the incentives should come from high political levels in all concerned countries in the Lake Victoria basin. Regional agreements would involve regional administration, authorities and importantly also local communities both close to the lake and upstream the basins. 

The key ecosystem services impacted by the regime shift are fisheries, freshwater, tourism, and local knowledge. The main user groups being affected are fishermen, other local community members working in the fishery or tourism industry, women, and children.

Fisheries: Fisheries have been the most important ecosystem service provided by Lake Victoria. Prior to the regime shift, they were exploited by small-scale fishermen, and the processing and trading sector was dominated by small-scale operators, most of them women from the local communities (Abila and Jansen 1997). The fish was for local consumption.

After the Nile perch boom and the collapse of the fish diversity, fishermen were at first opposed to the huge Nile perch which destroyed their equipment and was unsuitable for traditional preservation methods (Kaufman 1992). However, the situation changed and the fish became the main target as foreign aid and investors brought refrigerators and processing plants to the lake shore (ibid.), and an international market for the Nile perch developed.  The number of fishermen and people working in the harvesting, processing, and distributing sub-sectors of the fisheries rose immensely: During the 1980s, an additional 180,000 jobs were created (Abila and Jansen 1997).

The revenues generated by the fishery after the regime shift were greater than ever before (ibid.). However, also the distribution of wealth resulting from it differed from the original artisanal fishery. As indicated by many recent studies (Appleton 2000, Béné and Merten 2007, Geheb, et al. 2008), the new export-oriented fishing system was largely taken over by men. Women no longer had direct access to the fishing business, the fish itself, and the income generated by it. Fishermen began to often sell their fish to the exporting fish factories rather than bring it back to their families, re-invest their income into the fishery, or spend it on alcohol or sex workers (Geheb et al. 2008).

Despite the larger fish catches (Figure 2), malnutrition in many communities around the lake increased (ibid.). It had been widely assumed that this was due to the high export of fish protein (Reynold and Gréboval 1989) until more recent studies revealed that rather the socioeconomic gender inequalities have caused especially women and children to suffer from food insecurity. Often women, as the prime caretakers of children, have been forced into prostitution ("fish for sex") to maintain their livelihood (Béné and Merten 2007, Appleton 2000). This in turn has increased the number of HIV/Aids infections in the fishing villages after the regime shift (Appleton 2000).

Freshwater: Even before the Nile perch boom, the lake's ecosystem had already been altered by eutrophication (Kaufman 1992). However, it was able to cope with the alteration due to the high proportion of cichlids which provided tight internal recycling (ibid.). By wiping out the cichlid stocks, the Nile perch ultimately decoupled the recycling capacity of the lake (ibid.). Since drinking water is still often drawn directly from the lake with little or no treatment (Kansiime, Saunders, and Loiselle 2007), all local community members have been affected by this declining ecosystem service.

Tourism: Lake Victoria is increasingly becoming a tourist destination, partly due to sport-fishing (Lung'ayia, Sitoki, and Kenyanya 2001). After the regime shift, fishing tourists have been attracted by the huge Nile perch, the lake got known internationally, and hotels and tourism facilities were established, benefiting the people working in the tourism industry.

Knowledge: For local ecosystem and biodiversity knowledge, it can be assumed that much of the original diversity and complexity of the lake is now unknown to the local communities which would account as a general loss of this service.

Aesthetic values: The rising number of factories along the lake's shore as well as the decreasing water quality had most likely negative effects on the aesthetic values of Lake Victoria. The loss of this service would concern all community members. 

Nile perch is now showing signs of being overexploited and some of the native species that were either diminished or even believed to be extinct are returning (Balirwa et al. 2003). This might raise questions whether the Nile perch regime shift in the 1980s was an actual shift or a mere fluctuation. However, it is firmly established that there were profound changes in feedback mechanisms in Lake Victoria. We presume that the relentless fishing in the Lake is now causing the current Nile perch regime to become less resilient, allowing the cichlids to return. What will happen to the system if this is allowed to continue is uncertain. A possible scenario is that Lake Victoria returns to a regime similar to the cichlid dominated one, albeit with less species.

This raises a further question, namely how desirable such a shift would be. Although the Nile perch regime has inflicted heavy losses on some ecosystem services, the Nile perch boom generated more income from fishing than the previous state. From a socio-economical point of view, the fisheries in Lake Victoria are in a profitable state, although many social problems are associated with this business (Kitchell et al. 1997). Models have been developed to suggest fishing practices that would reduce predation on native species and at the same time make sure the fishing of Nile perch becomes more sustainable (ibid.). Whether such a regime compromise is viable in the long run is uncertain but with more targeted efforts and uniform policies it might be.