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International audience; Recently, the abundance of young Atlantic bluefin tuna (Thunnus thynnus) tripled in the northwestern Mediterranean following effective management measures. We investigated whether its predation on sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) could explain their concurrent size and biomass decline, which caused a fishery crisis. Combining the observed diet composition of bluefin tuna, their modelled daily energy requirements, their population size, and the abundance of prey species in the area, we calculated the proportion of the prey populations that were consumed by bluefin tuna annually over 2011-2013. To assess whether tuna could alter the size structure of the three small pelagic fish populations (anchovy, sardine, and sprat (Sprattus sprattus)), the size distributions of the consumed prey species were compared with those of the wild populations. We estimated that the annual consumption of small pelagic fish by bluefin tuna is less than 2% of the abundance of these populations. Furthermore, size selectivity patterns were not observed. We thus concluded that tuna predation is unlikely to be the main cause of major changes in the small pelagic fish populations from this area.

Industrial-scale fisheries are often thought to reduce food availability for top predators. It is essential to estimate the spatial and temporal overlap over a fine scale between fisheries and pre- dators during their breeding season, when their energy demand is greatest and when they are most spatially constrained, in order to understand and manage this potential impact on their populations. In the Benguela upwelling region, 2 endemic vulnerable seabirds, Cape gannets Morus capensis and African penguins Spheniscus demersus, mainly eat anchovy Engraulis encrasicolus and sardine Sardinops sagax, both of which are exploited by the purse-seine fishery. A recent eastward displace- ment of small pelagic fish off the South African coast has reduced fish availability for both birds and fisheries along the west coast. Using GPS-recorders, we studied the foraging dispersal of birds from 8 colonies containing 95% of the global Cape gannet and 60% of the global African penguin popu- lations to assess their overlap with fish catches. Despite the fact that bird data were gathered at very fine spatial and temporal scales (meters and hours), and fisheries data were recorded at much coarser spatial and temporal scales (20 km and months), there was clear overlap in areas used. The main for- aging areas of both species were located where purse-seine fisheries caught most fish, with most catches occurring during the birds' breeding season. As birds and fisheries also overlap in the size of the targeted prey and the depth of exploitation, our study suggests the potential for intense competi- tion between purse-seine fisheries and decreasing seabird populations in the southern Benguela. Long-term protection of these seabird species requires the inclusion of a suitable ecological buffer when setting fishery quotas, and implementing marine protected areas closed to fishing around key breeding sites and foraging hotspots may improve their breeding success.