Characteristics of Shark Bycatch Observed on Pelagic Longlines Off the Southeastern United States, 1992-2000

By Lawrence R. Beerkircher, E. Cortés, Mahmood Shivji. 2002

130 citations recorded by the source corpus.

Data collected by fisheries observers aboard U.S. pelagic longline vessels were examined to quantify and describe elasmobranch bycatch off the southeastern U.S. coast (lat. 22°–35°N, long. 71°–82°W). From 1992 to 2000, 961 individual longline hauls were observed, during which 4,612 elasmobranchs (15% of the total catch) were documented. Of the 22 elasmobranch species observed, silky sharks, Carcharhinus falciformis, were numerically dominant (31.4% of the elasmobranch catch). The catch status of the animals (alive or dead) when the gear was retrieved varied widely depending on the species, with high mortalities seen for the commonly caught silky and night, C. signatus, sharks and low mortalities for rays (Dasyatidae and Mobulidae), blue, Prionace glauca; and tiger, Galeocerdo cuvier; sharks. Discard percentages also varied, ranging from low discards (27.6%) for shortfin mako, Isurus oxyrinchus, to high discards for blue (99.8%), tiger (98.5%), and rays (100%). Mean fork lengths indicated the majority of the observed by-catch — regardless of species — was immature, and significant quarterly variation in fork length was found for several species including silky; dusky, C. obscurus; night; scalloped hammerhead, Sphyrna lewini; oceanic whitetip, C. longimanus; and sandbar, C. plumbeus; sharks. While sex ratios overall were relatively even, blue, tiger, and scalloped hammerhead shark catches were heavily dominated by females. Bootstrap methods were used to generate yearly mean catch rates (catch per unit effort) and 95% confidence limits; catch rates were generally variable for most species, although regression analysis indicated significant trends for night, oceanic whitetip, and sandbar sharks. Analysis of variance indicated significant catch rate differences among quarters for silky, dusky, night, blue, oceanic whitetip, sandbar, and shortfin mako sharks.

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Citations in the corpus

• Shark interactions in pelagic longline fisheries (2008, background): “[33] found that the condition of sharks caught in pelagic longline gear (dead versus alive when hauled to the vessel) varied widely by species, where, for example, blue sharks had a relatively low 12.”
• Inferring shark population trends from generalized linear mixed models of pelagic longline catch and effort data (2010, background): “%) in the fishery each year since (Beerkircher et al., 2004).”
• Vulnerability of oceanic sharks as pelagic longline bycatch (2014, background): “, 2014b) and very low (2%–8%) mortality in pelagic and bottom longlines (Beerkircher et al., 2002; Morgan and Burgess, 2007;Morgan and Carlson, 2010).”
• Small cetacean captures in Peruvian artisanal fisheries: High despite protective legislation (2010, methodology): “Independent onboard observer programs have been widely used as an effective means to quantify bycatch (e.g. Gales et al., 1998; Beerkircher et al., 2002; Carretta et al., 2004; Rogan and Mackey, 2007), and have been specifically recommended in the case of small cetacean captures in Peru (Reeves et a”
• Shark bycatch and depredation in the U.S. Atlantic pelagic longline fishery (2008, background): “These downward trends may reflect shifts in abundance, but could also be indicative of spatial and gear factors that have served to reduce catchability (Beerkircher et al. 2002).”
• Global catches, exploitation rates, and rebuilding options for sharks (2013, unknown): “1 413,873 [59] Swordfish Atlantic Southeast 1998–2005 2.”