Response of fish stocks in Lake Victoria to enforcement of the ban on illegal fishing: Are there lessons for management?

Most small-scale inland fisheries in the Global South prohibit fishing gear with smaller meshes than is legally permitted. Nonetheless, in most instances, this is not strictly enforced. But starting in 2017, Uganda and Tanzania ramped up enforcement on Lake Victoria. We used time series hydro-acoustic data to determine whether the strict enforcement achieved the management goal of increased biomass (t) of commercial species and an increase in the biomass of big Nile perch (>50 cm). The biomass for 2018–2021 (under strict enforcement) was expected to be greater than in 2007–2017 (prior to strict enforcement). The biomass of key species fluctuated annually, but no spatial or temporal differences in biomass associated with strict enforcement were evident. Similarly, the biomass of big Nile perch did not increase. Our findings suggest that mesh sizes may have limited influence on fish biomass dynamics in Lake Victoria, and that high primary productivity of the lake, high turnover rates of fish species, and limited compliance by fishers likely counteract the effects of high fishing effort on biomass and size structure of fish. Therefore, the high cost of strict top-down enforcement and the societal cost of lost lives, jobs, and livelihoods may not be justified.