The Chronology of Overfishing in a Remote West-African Coastal Ecosystem

Classic studies of marine overexploitation traditionally analyze cases of "fishing down the food web": turning to smaller species at lower trophic levels after depleting the larger top predators. Much less documented, however, is the preceding phase in which higher trophic level species, previously not exploited or consumed locally, are increasingly added to the catch. Worldwide, this phase happened centuries ago due to technological developments and thus passed before scientific scrutiny and conservation awareness arose, leaving it largely unstudied. Here, we combine a historical reconstruction of fishery with a relatively recent fishing monitoring program to document this early phase in the Parc National du Banc d'Arguin in Mauritania, a marine protected area in Mauritania, West Africa. Long-term trends in mean trophic level of exploited species and total catches provide evidence for an increasing fishing pressure toward the top of the food web, and suggest that the state of "fishing down the food web" is now happening in this ecosystem. This involves the recent intensive targeting of rays and sharks. We show that their contribution to the local economy is marginal compared with the traditionally fished species.