Characteristics of Shark Bycatch Observed on Pelagic Longlines off the Southeastern United States, 1992–2000

Beerkircher, Lawrence R. and Cortés, Enric and Shivji, Mahmood (2002) Characteristics of Shark Bycatch Observed on Pelagic Longlines off the Southeastern United States, 1992–2000. Marine Fisheries Review, 64(4), pp. 40-49.

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Official URL: http://spo.nwr.noaa.gov/mfr644/mfr6443.pdf

Abstract

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.

Item Type: Article
Title: Characteristics of Shark Bycatch Observed on Pelagic Longlines off the Southeastern United States, 1992–2000
Personal Creator/Author:
CreatorsEmail
Beerkircher, Lawrence R.
Cortés, Enric
Shivji, Mahmood
Refereed: Yes
Journal or Publication Title: Marine Fisheries Review
Volume: 64
Number: 4
Page Range: pp. 40-49
Date: 2002
ISSN: 0090-1830
Issuing Agency: United States National Marine Fisheries Service
Subjects: Biology
Ecology
Fisheries
Management
Item ID: 9741
Depositing User: Patti M. Marraro
Date Deposited: 16 Aug 2012 13:19
Last Modified: 16 Aug 2012 13:19
URI: http://aquaticcommons.org/id/eprint/9741

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