Catch, Bycatch of Sharks, and Incidental Catch of Sea Turtles in the Reunion-Based Longline Swordfish Fishery (Southwest Indian Ocean) Between 1997 and 2000

Abstract

Data from voluntary logbooks (5,884 longline sets) collected between 1997 and 2000 were analyzed to assess the potential impact of the Reunionbased longline swordfish fishery (South West Indian Ocean) on sharks and on sea turtle populations. Blue shark (Prionace glauca) represented between 75% and 88% of the total catches of sharks studied. Bycatch discarding varied with species, ranging from low discard (2.6%) for mako shark (Isurus sp.) to high discards for blue shark (86.5%). Estimation of the total catch of sharks (retained and discarded individuals) represented in weight between 7% and 9% of the total catch of the major species caught by the fishery. Of concern is the decline of blue shark CPUE (Catch Per Unit of Effort) from 2.2 to 1.03 sharks per 1,000 hooks between 1998 and 2000. Of the 22,974 hook-timers deployed during cruises onboard commercial, 49% of the blue shark (Prionace glauca) and 41.2% of the oceanic whitetip shark (Carcharhinus longimanus) were retrieved alive. It was assumed that among the 15,250 blue sharks caught during this period, at least 7,099, released alive, could have survived. The observed sea turtle catch rates were low compared with those reported for other longline fisheries. The fishery had47 interactions with Leatherback(Dermochelys coriacea), 30 with Hawksbill turtles (Eretmochelys imbricata), and 16 with Green turtles (Chelonia mydas).