CHIPOLATA - Climate change and harvesting impacts on the pelagic fish community of Lake Tanganyika

The pelagic ecosystem in Lake Tanganyika is of tremendous importance for biological diversity and the local communities around the lake. The nearly 100,000 fishermen catch up to 200,000 tonnes of fish each year. In comparison, only cod and herring have larger catches in the Norwegian fisheries. Most of the catch includes two small fish species, Stolothrissa tanganicae and Limnothrissa miodon, often called "freshwater sardines", along with a larger fish, Lates stappersii. The fishery is nutritionally and economically important for over 10 million people who live around the lake. However, the fish are at risk of decline due to climate change and overfishing. While overexploitation may lead to direct declines, the warming climate may cause stronger stratification of the water layers. This can lead to less plant and animal plankton growth, and thus less food for the fish. The aim of this project is to clarify the effects of climate change and harvesting on the fish stocks of Lake Tanganyika. To do so, we will study how much the fish have changed over the past 30 years by comparing fish collections from 1995 and the present. We will use new genetic methods that can find out if there has been a decline in fish stocks, and that can tell us how the fish are adapting to a changing environment. We will also analyse the fish's feeding habits: has there been changes in their diet? Finally, we will investigate if the three species are growing slower or faster in size than in the past. Together, this will tell us whether the fish's ecological roles have changed over time, and how vulnerable they are to climate change and fishing. We will also analyse which changes in the fish stocks may have consequences for the fishery. Throughout the project, we will collaborate with local researchers, fishermen and authorities to collect fish, analyze the data, and discuss how our findings can improve fisheries management in Lake Tanganyika and elsewhere.

Lake Tanganyika has enormous ecological and economic value. Its biodiversity and the productivity of its pelagic fishery providing food to ~10 million people are astonishing. The three economically most important pelagic species, the freshwater clupeid Stolothrissa tanganicae and Limnothrissa miodon, and the latid perch Lates stappersii represent more than 90 % of annual catches (200 000 tons/year). However, sustainable harvesting of these fishes is threatened by the impacts of climate change and overfishing. To what extent these pressures have affected the pelagic ecosystem and its fish community remains unclear. An understanding of these risks is urgently needed to allow an informed choice between appropriate management strategies. To better understand the resilience of the pelagic fish community, we will use recent and historical collections of fish to study changes in three key aspects of fish biology across a 30-year (1995-2025) time window: stock structure, trophic ecology, and growth. In WP1, we will collect new biological samples of the three fishes across the lake, guided by existing scientific and local knowledge. In WP2, we will generate whole genome sequencing data to investigate changes in lake-wide stock structure and effective population size, an important indicator for the genetic vulnerability of fish stocks. We will also mine these data for genomic signatures of selection. In WP3, we will study changes over time in trophic morphology, diet, and trophic position. In WP4, we will study changes in fish growth dynamics. In WP5, we will compare the magnitude of all biological changes over time and develop biological indicators for stock vulnerability to climate change and harvesting. In WP6, we partner throughout the project with local scientists, fishers, and authorities to make our findings accessible and promote their integration in fisheries management. The project will be managed (WP7) with direct participation of the stakeholders from the start.