LAKE TURKANA’S FISHERIES: NEW INSIGHTS FROM A CENTURY OF LIMNOLOGICAL RESEARCH

Fish have become an important food resource in East Africa, and the development of African Great Lakes fisheries contributes to nutrition, employment, and livelihood security. Lake Turkana, a transboundary rift valley lake on the border of Kenya and Ethiopia, is an important source of fish for both local consumption and international trade. Lake Turkana’s fisheries have expanded throughout the last century, and fisheries productivity is closely tied to regional climatic variability. Boom-and-bust fishery cycles in Lake Turkana are likely driven by a combination of fishing pressure, fishing practices, and environmental variables. Although Lake Turkana’s fisheries productivity cycles are driven in part by fluctuations in water level, commercial fishing has likely contributed additional destabilizing effects to fish population dynamics and increased susceptibility of stocks to collapse. As fishing is inherently selective, selection pressure from heavy exploitation of fish stocks often drives shifts in fish life history traits including mean length, maximum length, and size at maturity that can serve as indicators of heavy fishing. Over the last century, lake-wide limnology and fisheries surveys have been sporadic but act as important historical snapshots that capture changes in the life histories and trophic dynamics of Lake Turkana’s fish species. Analysis of historical survey data has revealed shifts toward earlier maturation at smaller body sizes in several of Lake Turkana’s commercially targeted fish species. While recognizing that environmental conditions may have played a role in shaping life history traits, the direction and magnitude of the shifts in life history traits are consistent with expected effects of heavy fishing. These shifts may influence not only fisheries productivity but have cascading effects on predator-prey interactions and the lake’s trophic ecology. In understudied regions like Lake Turkana, disentangling the effects of fishing and climate change on fish life history and trophic dynamics is important for the future sustainability of the lake’s fish stocks. For Lake Turkana, the focus of future research should shift toward assessing the combined effects of environmental fluctuations and fishing on the lake’s ecology through the development of long-term limnological and fisheries monitoring programs.