Seabird bycatch in the demersal longline fishery off southern Africa

Abstract

This study assesses seabird bycatch in the demersal longline hake (Merluccius capensis and M. paradoxus) fishery in the southern Benguela region. Observers collected seabird bycatch data from 2 412 sets (14 million hooks) in the South African fishery, accounting for 6.8% of total effort for the period 2000–2006. Of the 107 seabirds caught, at a rate of 0.008 per 1 000 hooks, 41 were killed (0.003 per 1 000 hooks). There was a significant decrease in catch rate, from 0.033 per 1 000 hooks in 2000 to 0.001 per 1 000 hooks in 2006. An estimated total of 225 (range 220–245) birds were killed per year by the South African fishery. Vessel, area and light conditions were all significant  predictors of seabird bycatch. The white-chinned petrel Procellaria aequinoctialis was the species most commonly caught by the South African fleet, at a rate of 0.0027 per 1 000 hooks. From interviews with 13 observers and six members of the Namibian demersal longline  fishery, seabird bycatch was estimated at 0.05 per 1 000 hooks and 0.13 per 1 000 hooks respectively. Observations were taken during four trips in Namibian waters in November 2006, in which 21 sets (456 000 hooks) were monitored. White-chinned petrels were killed at a rate of 0.14 per 1 000 hooks during these trips. Differences in catch rates between trips were investigated and moon phase, area and gear type  were all found to be significant. All birds were caught using light gear, which sank significantly slower than heavier gear. The South African hake longline fishery has a relatively small impact on pelagic seabird  populations compared with the Namibian fishery.

Keywords: bycatch, demersal longline, Namibia, seabirds, South Africa

African Journal of Marine Science 2009, 31(2): 205–214