Climatic change and declining water quality
Fish in EASLs are very probably highly impacted by the ongoing global climate changes in their shallow saline basins, where they are exposed to increasing temperatures, salinity and high levels of ultraviolet B (UVB) radiation. Fragmentation of the lakes and salinization of habitable sections may result in reduced refuge sites for the fish. This may subsequently lead
to disappearance of the populations. In recent years, soda lakes have been exploited for soda ash extraction, water extraction for agriculture, and geothermal power generation, and have become sites of active development (Stiassny & Getahun 1998; Lemma 2003; Klemperer &
Cash 2007; Yongo et al. 2010; Philip & Mosha 2012). These human-mediated activities are associated with pollution and decline in water quality and pose great challenges to the long-term existence of saline lake fisheries.
Migration and movement
Saline lakes and their fish populations stretch across jurisdictional boundaries; often their occurrence and movement cut across political boundaries. This raises trans-boundary issues of mutual concern among the member states involved. For instance, although the greatest portion of Lake Turkana is found in Kenya, most of its inflow (90%) comes from the Omo River in Ethiopia (Avery 2010; Muška et al. 2012). Similarly, Lake Natron in Tanzania receives its major fresh water inflow from the Ewaso Nyiro River in Kenya. Proposals by the Ethiopian and Kenyan governments to dam the waters of the Rivers Omo (Ojwang et al. 2010) and Ewaso Nyiro, respectively, have raised concerns among conservationists over the effects both projects may have on biodiversity of the respective lakes. Clearly, there is a need for the countries to develop policies that ensure equitable sharing and conservation of the lakes resources. However, history has shown that cooperative management of trans-boundary resources is hindered by lack of common laws among member states. Another challenge to such mutual agreements is the fact that too many institutional players are involved. This complicates the formulation of conservation strategies. Delineation of the movements of fish in EASLs is also important in determining the dispersal ability and distribution ranges of individual species. Such information is in turn useful for conservation purposes and for assessing the effects of various species interactions.
Competing interests
The need to strike a balance between economic development and conservation of wetlands remains a thorny issue among key stakeholders. For a long time, EASLs have sustained the subsistence livelihood of the surrounding communities. In turn, the communities have protected the lakes to ensure a continued supply of their resources. However, in recent years there has been an influx of local and foreign-owned companies into the saline lakes. For instance, there have been concerns that construction of the proposed Gibe 3 hydroelectric dam on the Omo River by the Ethiopian government may alter the seasonal flooding cycle of
Chapter 2 Fish Populations in East African Saline Lakes
the river (Ojwang et al. 2010). This may cause irreversible changes to Lake Turkana, whose major water input comes from River Omo. Dwindling water resources in Lake Turkana have been shown to contribute to conflicts among farmers, pastoralists and fishermen who depend on the lake’s water (Yongo et al. 2010). Lakes Abijata and Magadi are heavily mined for soda ash (Hughes 2008). Recently, there was a proposal to establish a similar mining plant in Lake Natron. Many of the projects are executed following government approvals or by the governments themselves without full consideration of the potential impacts on fish populations or general aquatic ecosystem health. However, drawing lessons from other studies, such projects may result in irreversible destruction of the fish communities through pollution, loss of gene pools, habitat fragmentation and destruction (Roberts 1993; Avery 2010). Perceived benefits from such projects, e.g. employment creation and improved livelihoods, may further contribute to the socioeconomic gap between development and conservation.
Adverse effects of introductions of other fish species into saline lakes
Although saline lakes have been least affected by human-mediated species introductions, several cases of alien species have been reported in some saline lakes. The introduction of Magadi tilapia to Lake Nakuru between 1952 and 1962 to control mosquitoes is probably the most well-known case (Vareschi 1979). The species has also been introduced to Lake Elementaita (Okeyo 2006). Other species introductions have also been reported in Lake Turkana. A good example of the detrimental effects of fish introductions to saline lakes is the case of Lake Chilotes in Ethiopia (Lemma 1994). Lake Chilotes was a typical saline lake until 1990, when a government initiative through the Ministry of Agriculture diverted River Mori into Lake Chilotes in an attempt to increase water for irrigation (Lemma 2003). Consequently, the salinity of the lake started to decrease, favoring the colonization of the lake by three Barbus species from River Mori. The introduced species have since led to a marked decrease of Lake Chilotes’ native O. niloticus species (Lemma 2003). In general, such introductions risk destabilizing existing ecosystems.
Conclusions
The future of saline lakes and their fish populations in East Africa remains uncertain. In some cases, prompt interventions may be required to save the remaining local populations from extinction. This would require extensive surveys to collect data on species composition,
distribution, life history traits and other aspects of individual fish populations. It is hoped, therefore, that the present information will serve as a guide in formulating conservation plans. As it has already been demonstrated in some alkaline lakes (e.g. Lake Turkana), EASLs can support more fish species than they currently contain. Given the challenges and threats associated with introduction of alien fish species in EASLs, we recommend management and conservation strategies aimed at preserving native fish populations. In lakes that have lost their fish populations or have no known fish populations of their own, introduction of fish from localities naturally connected to the lakes in question may be an option. However, caution should be taken to ensure that only species that have high probability of survival and recruitment are introduced to EASLs to maximize colonization success. Other important aspects to consider before such introductions include: the availability of food, disease and vectors, as well as the effects the fish may have on other components of the target lake’s ecosystem. Management and conservation of EASLs and their fish populations requires the commitment of multiple stakeholders including local communities, fisheries managers, scientists, regional and national governments, and the international community at large. In particular, the East African Community should formulate and enforce strict policies and laws to govern utilization, management and conservation of EASLs resources. Strategies aimed at forging a good working relationship among all potential users would be a major step towards a realistic and sustainable conservation framework.
Acknowledgements
This work was supported by various grants. GDK is supported by a collaborative scholarship grant from the Deutscher Akademischer Austausch Dienst (DAAD) and Kenyan Ministry of Education, Science and Technology (MOEST). AM is supported by the University of Konstanz, grants of the Deutsche Forschungsgemeinschaft and the European Research Council. CMW is supported by the Canada Research Chair Program, and grants from the Natural Sciences and Engineering Research Council of Canada (NSERC). We thank Papah Babak, Ora Johannsson, Daniel Msafiri Shayo and Ayub Oduor for useful discussions during the preparation of this manuscript. We appreciate the logistical support by Tata Chemicals Magadi (formerly Magadi Soda Company) during several research expeditions in which some of the observations and data reported in this chapter were collected.