A cross-taxa assessment of pelagic longline by-catch mitigation measures: conflicts and mutual benefits to elasmobranchs

Gilman, Eric and Chaloupka, Milani and Swimmer, Yonat and Piovano, Susanna (2016) A cross-taxa assessment of pelagic longline by-catch mitigation measures: conflicts and mutual benefits to elasmobranchs. Fish and Fisheries, 17 (3). pp. 748-784. ISSN 1467-2960

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Abstract

Elasmobranch mortality in pelagic longline fisheries poses a risk to some populations,
alters the distribution of abundance between sympatric competitors, changing
ecosystem structure, processes and stability. Individual and synergistic effects on elasmobranch
catch and survival from pelagic longline gear factors, including methods
prescribed to mitigate bycatch of other vulnerable taxa, were determined. Overall
relative risk of higher circle vs. J-shaped hook shark catch rates conditioned on potentially
informative moderators, from 30 studies, was estimated using an inverse-precision
weighted mixed-effects meta-regression modelling approach. Sharks had a 1.20
times (95% CI: 1.03–1.39) significantly higher pooled relative risk of capture on
circle hooks, with two significant moderators. The pooled relative risk estimate of ray
circle hook catch from 15 studies was not significant (RR = 1.22, 95% CI: 0.89–
1.66) with no significant moderators. From a literature review, wire leaders had
higher shark catch and haulback mortality than monofilament. Interacting effects of
hook, bait and leader affect shark catch rates: hook shape and width and bait type
determine hooking position and ability to sever monofilament leaders. Circle hooks
increased elasmobranch catch, but reduced haulback mortality and deep hooking relative
to J-shaped hooks of the same or narrower width. Using fish vs. squid for bait
increased shark catch and deep hooking. Pelagic stingray (Pteroplatytrygon violacea)
catch and mortality were lower on wider hooks. Using circle instead of J-shaped
hooks and fish instead of squid for bait, while benefitting sea turtles, odontocetes and
possibly seabirds, exacerbates elasmobranch catch and injury, therefore warranting
fishery-specific assessments to determine relative risks.

Item Type:	Journal Article
Subjects:	G Geography. Anthropology. Recreation > GE Environmental Sciences S Agriculture > SH Aquaculture. Fisheries. Angling
Divisions:	Faculty of Science, Technology and Environment (FSTE) > School of Marine Studies
Depositing User:	Fulori Nainoca - Waqairagata
Date Deposited:	16 Jun 2017 03:03
Last Modified:	16 Jun 2017 03:03
URI:	https://repository.usp.ac.fj/id/eprint/9967

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