Pelagic shark bycatch in the tuna and swordfish directed longline fishery off southern Africa

Petersen S L, Honig MB, Ryan PG, et al (2009) Pelagic shark bycatch in the tuna and swordfish directed longline fishery off southern Africa. African Journal of Marine Science 31:215–225.

Southern African waters are an interesting region to study the viability of shark capture because of the diversity of vulnerable species and the existence of a pelagic longline fleets which catch sharks as a bycatch when targeting tunas or Swordfish. A total of 20 species was caught as bycatch by the South African pelagic longline fleets targeting tuna Thunnus spp. and Swordfish Xiphias gladius, 1998-2005, six of which are considered Vulnerable and one (Scalloped Hammerhead Sphyrna lewini) Endangered. Blue Prionace glauca and Short-finned Mako Isurus oxyrinchus Sharks were the most commonly caught species (69.2% and 17.2% respectively of sharks caught). Swordfish-directed vessels caught more sharks (11.7 Blue Sharks/1000 hooks and 1.4 Short-finned Mako Sharks/1000 hooks) compared with tuna directed vessels (1.8 Blue Sharks/1000 hooks and 0.9 Short-finned Mako Sharks/1000 hooks). The catch per unit effort (CPUE) of Blue Sharks and Short-finned Mako Shark decreased from 2001 and 2000 respectively. This was accompanied by a decrease average in length frequency for both species, 2002–2007. Between 39 000–74 000 (depending on extrapolation technique) sharks are caught as bycatch per year, 1998–2005. The proposed increase in fishing effort to 50 rights holders (targeting tunas and Swordfish), could increase the fishing effort threefold from 6.4 to 20 million hooks per year. If the distribution of fishing effort remains constant shark bycatch could increase to approximately 134 000 or 3 000 t of sharks per year.