An integrated approach for a sustainable clupeid fishery on Lake Tanganyika

The aim of this thesis is to contribute to sustainable fisheries of two species of sardines in Lake Tanganyika (LT). It is the longest (650 km) and second deepest (1430 m) lake in the world. The fisheries of LT are extremely productive with an estimated annual catch of 200,000 tonnes feeding hundreds of thousands of people in the neighbouring countries: Burundi, DRC, Tanzania and Zambia. The main catch is composed of just three endemic pelagic fishes: two species of clupeid fishes (sardines): Stolothrissa tanganicae and Limnothrissa miodon, and a species of Nile perch: Lates stappersii. There is a great uncertainty on the sustainability of the LT fisheries as this appears to be highly sensitive to climate change, decreased primary production and overfishing. The latter is considered, including by authorities in the neighbouring countries, a major threat to biodiversity and sustainable fisheries. Between 2002 and 2014, the number of fishers on the Lake has doubled because of an influx of refugees, while catch rates have declined steadily. Observations at landing sites show evidence of depletion of fish stocks. Although the two species of clupeids have dominated catches for a long time, large knowledge gaps remain regarding their biology and behaviour. For example, do different stocks inhabit the Lake and why and how do fish migrate within the Lake? LT might harbour distinct stocks of both S. tanganicae and L. miodon based on otolith micro-chemistry, but conclusive genetic evidence to support this has yet to be provided, necessitating a genomic approach to increase resolution and the number of markers available. Improved knowledge is essential to avoid a mismatch between biological stock structure and management units. The lack of sufficient knowledge on the biology of the main fish species including genetic diversity and shoal movements (or migration) hinders the development of appropriate management strategies, vital for the future of the LT fishery. In DRC, the country with the longest LT shoreline, the national government mentions lack of knowledge, lack of correct quota, lack of stakeholder involvement and lack of specialists as reasons for uncontrolled and illegal fisheries. The first objective of this thesis is to identify stock structure with phenotypic and genetic methods. Population genomics allows to detect the genetic structure and demographic stability and to measure adaptive potential and resilience to environmental change. Genetic profiling with Single Nucleotide Polymorphisms (SNPs) will reveal population structure, the level of gene flow, and the scale of adaptation to lake-wide environmental gradients. The second objective is to make use of knowledge from key informants, such as fishermen, scientists and policy makers. Using semi-structured interviews, we aim to generate an overview of their state of knowledge, opinions and concerns on clupeid fishes and fisheries. We will survey the perceived decline of clupeid species abundance and the attitude towards catch restrictions and other management strategies, giving us an overview of strategies that would be supported by the community. All research is conducted in close collaboration with our Congolese partner, the CRH in Uvira.

Publication year:2021

Accessibility:Open