Effect of trawling on bird and seal distributions in the southern Benguela region

Abstract

Attendance patterns of seabirds and Cape fur-seals Arctocephalus pusillus pusillus at research trawls in the southern Benguela region during the austral winter are analysed to infer the importance of trawl fisheries to different seabird and seal species. Three specific responses to trawlers are recognized: ( 1 ) species that avoid feeding assemblages at trawlers (jackass penguin Spheniscus demersus, soft-plumaged petrel Pterodroma mollis, Cape cormorant Phalacrocorax capensis); (2) species that cons~stently are attracted to trawlers and whose distributions are influenced by trawlers (black-browed albatross Diomedea melanophris, shy albatross D. cauta, pintado petrel Daption capense, white-chinned petrel Procellaria aequinoctialis); (3) species that only forage at trawlers in deep, offshore waters (Cape gannet Sula capensis, kelp gull Larus dominicanus, Cape fur-seal). Other species lie between these extremes. These variations in response indicate the importance of trawler discards in each species' diet. The divisions do not follow the guild classification used for the region to date. Reported increases in seabird populations as a result of trawling activity should be interpreted with caution.