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Spatio-temporal and length distributions of istiophorids in the southwest Indian Ocean inferred from scientific, observer and self-reporting data of the Reunion Island based pelagic longline fishery








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    Assessment of depredation level in Reunion Island pelagic longline fishery based on information from self-reporting data sampling programme 2013
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    Depredation attracts broad intertiol attention during recent decades with worldwide expansion of fishing by passive gears, in particular pelagic and bottom longlines. Presumed steady increase of depredation level from the early years of fisheries to present (IOTC, 2000a, Donoghue et al., 2003, Gilman et al., 2007) and economic losses associated with this type of interaction (IOTC, 1999, 2000a, Bargain, 2000, 2001; Nishida, Tanio, 2001, Rabearisoa, 2012) were major concerns. Depredation is usuall y defined as “the partial or complete removal of hooked fish or bait from fishing gear...” by predators such as cetaceans, sharks, bone fish, birds, squids, crustaceans and others” distinguishing it from predation, i.e. “the taking of free swimming fish (or other organisms)...” (Donoghue et al., 2003; Gilman et al., 2006, 2007). Depredation mostly occur in statiory (passive) gears like pelagic and bottom longlines (Kock et al., 1996; Gilman et al., 2006, 2008), gillnets (Read et al., 2003), trap s, line fisheries (de Stephanis, 2004; Navarro, Bearzi, 2007) and within aquaculture facilities (Stickley et al., 1992; Coon, 1996; Glahn et al., 1999; Fenech et al., 2004; Kloskowski, 2005). However highly mobile fisheries like trolling, trawl and purse seine are also sometimes subject to depredation (often mixed with scavenging) by marine mammals (Zollett, Read, 2006, Zahri et al., 2004), squids (Olson et al., 2006), birds (Baker et al., 2007) or sharks (our unpublished data). Longline fishing operations suffered probably the most from depredation due to its worldwide distribution, statiory ture, long exposure (hours) in the environment, easy access to animal caught and gear fragility. Possible altertion of predators behaviour resulted from interactions with fishing gears was also suggested based on fact of depredation itself and different reaction to fishing gear among populations of the same species (Matkin et al., 2007). If alteration of predators? behaviour is really take place, potential wide impact on ecosystem scale might be envisaged. Depredation occurrence and respective losses of catch are usually not reported in the fisheries statistics and are a source of „cryptic mortality? that is not accounted for in current stock assessment studies, therefore affecting directly fisheries magement decisions and practice (Gilman et al., 2007, Romanov et al., 2007). Economic losses due to catch and gear damage have brought serious concerns to fishermen (Yano, Dahlheim, 1994; Ni shida, Tanio, 2001; Donoghue et al., 2003; Rabearisoa, 2012) while harm to marine megafau either through interactions with fishing gears or with fishermen who attempts to protect their catch (Gulland, 1986; Read, 2008) rises conservation issues. There is an obvious and urgent need for close monitoring of the depredation phenomenon, its quantification, incorporation into the fisheries magement schemes and development of mitigation measures. Here we report prelimiry results of depredation affectin g the local longline fishery operated from Reunion Island, basing on information from self-reporting data collection programme.
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