Albatross overlap with fisheries in the Benguela Upwelling System: implications for conservation and management

Trawl activity on the continental shelf break off South Africa provides large quantities of food in the form of discards for a range of species, including non-breeding black-browed albatrosses Thalassarche melanophrys and white-capped albatrosses T. steadi. As large numbers of both species are killed in collisions with trawl warp cables, mitigation measures have been introduced that include limitation of discards, yet little is known about the consequences of reduced food supply for scavenging birds. We tracked adult and immature albatrosses in the southern Benguela in the austral winters of 2005 and 2006 and examined their distribution in relation to fisheries, bathymetry and remotely sensed oceanography. Kernel analysis revealed that white-capped albatrosses spent most (85.0%) of their time on the southern African trawl grounds, whereas black-browed albatrosses spent only 39.2% of their time in these areas, and the remainder on return oceanic foraging trips, typically of 8.4 d duration and 2540 km (max. 5320 km) in length. While foraging in South African waters, the presence of trawlers was a strong predictor of albatross distribution. While on oceanic foraging trips, black-browed albatrosses moved predictably along the margins of eddies, typically areas of enhanced productivity and high prey concentrations. This study presents evidence that black-browed albatrosses forage to a much greater extent on natural prey than do white-capped albatrosses. Therefore, given the high incidence of albatross collisions with trawl cables, the benefit of a management decision to limit discarding as a mitigation measure is likely to outweigh the disadvantage of reduced food.