Title: Incidental and bycatches of sharks and turtles in the Reunion Island swordfish longline fishery in the Indian Ocean (1994-2000)
Abstract: The Indian Ocean swordfish longline fishery based in Reunion Island started operating in 1991. Between 1994 and 2000, Ifremer 1 collected data from voluntary logbooks and regular at-sea and port sampling programmes. 5885 longline sets were examined to quantify the catches of five major shark species caught by the domestic longline fleet between 1997 and 2000: blue shark (Prionace glauca), Oceanic whitetip shark (Carcharhinus longimanus), shortfin mako (Isurus oxyrinchus), hammerhead sharks (scalloped hammerhead Sphyrna lewini and smooth hammerhead Sphyrna zygaena combined). Blue shark (Prionace glauca) was dominant in the catch with an average of 180 t per year between 1997 and 2000; this represented between 75% and 88% of the total catch of sharks. Mean catch rates for blue shark, oceanic whitetip shark were significantly higher for the small sized vessels (less than 16 m) operating in the immediate vicinity of the island, during the whole period (Kruskal-Wallis test, p<0.05). Significant decreases of the catch rates were observed for these two species from 1998 to 2000, declining from 2.2 to 1.03 blue sharks per thousand hooks and from 0.13 to 0.07 oceanic whitetip sharks per thousand hooks as the fishing effort of this boat category increased twofold over the same period. Results using hook-timers indicated that 52 % of the blue shark and 59 % of the oceanic whitetip shark were retrieved dead and around 50% died within 6 to 8 hours after being hooked. 6,516 of the 13,325 blue sharks caught were released alive and it is estimated that after four months, 5,558 were still alive (41.5%). These results suggest that only a portion of discarded shark should be when considering species-specific management measures, as species with high survival rates may substantially reduce bycatch mortality. The amount of size data recorded was very low for all the shark species and limits its use; nevertheless for blue shark the size ranged from 64 to 289 cm (FL), this average was 195.5 cm FL and about 40 % of specimens measured were less than the size of sexual maturity (i.e., <185 cm FL). During 1996 and 2000, the fishery recorded 97 interactions with turtles: 51 with leatherback, 30 with hawksbill and 16 with green turtles. The catch status of the turtles (alive or dead) when the gear was retrieved varied depending on the species, but in most of the cases, they were released alive. This study underscores the need to conduct experiments to gain information about long-term survival of released bycatch species.
Publication Year: 2007
Publication Date: 2007-01-01
Language: en
Type: article
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Cited By Count: 3
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