Overlap between vulnerable top predators and fisheries in the Benguela upwelling system: implications for marine protected areas

Abstract

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 predators 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 displacement 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 populations 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 foraging 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 competition 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.

Breaking the routine: individual Cory's shearwaters shift winter destinations between hemispheres and across ocean basins

“…Finally, Cory's shearwater populations have a wide variety of potential wintering sites from which individuals may choose [28]. It is highly probable that the relative quality of each of these wintering quarters varies temporally as a consequence of physical forcing [30] and top-down processes, for example, fishing pressure [31]. This raises the question of whether Cory's shearwaters have enough plasticity in their migratory behaviour to quickly respond to such changes, which has important implications for their ability to adapt to longer term environmental shifts.…”

Marine no-take zone rapidly benefits endangered penguin

“…Their survival and breeding success are closely tied to the availability of pelagic sardines (Sardinops sagax) and anchovies (Engraulis encrasicolus) within 20-30 km of their breeding sites (Pichegru et al 2009). During their life, these fish can cover large distances (over hundreds of kilometres, Barange et al 1999).…”

Using habitat models for chinstrap penguins Pygoscelis antarctica to advise krill fisheries management during the penguin breeding season

“…Developing reference control sites for comparison with fished sites is now vital for disentangling the confounding effects of climate change, fishing and changes in recovering marine mammal populations. Attempts to experimentally determine how fisheries deplete forage fish stocks and therefore impact dependent species have shown that fishing near-shore can increase the range of foraging trips and impact chick survival, leading to considerable change in population size (Bertrand et al, 2012;Pichegru et al, 2009;Sherley et al, 2015). Additionally, the foraging efficiency of breeding seabirds may be significantly affected by not only the regional quantity, but also the temporal and spatial patterns of prey removals.…”