Fish and fisher behaviour influence the vulnerability of groupers (Epinephelidae) to fishing at a multispecies spawning aggregation site

Robinson, Jan, Graham, Nicholas, Cinner, Joshua, Almany, Glenn, and Waldie, Peter (2015) Fish and fisher behaviour influence the vulnerability of groupers (Epinephelidae) to fishing at a multispecies spawning aggregation site. Coral Reefs, 34 (2). pp. 371-382.

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Abstract

Targeted fishing of spawning aggregations is a major contributor to extinction risk in numerous species of grouper (Epinephelidae). Marine reserves are often used to protect spawning aggregation sites, including multispecies sites shared by several species of grouper. However, marine reserves may be biologically, socioeconomically or culturally unviable in some fisheries, and alternative management actions must be explored. Implementing effective management actions that control rather than prohibit fishing requires an improved understanding of how species vary in their vulnerability to fishing gears and respond to changes in fishing effort. To estimate sources of variability in vulnerability to fishing (i.e. catchability), catch-per-unit-effort (CPUE) and other fisheries data were collected in parallel with underwater visual census-derived estimates of aggregation size at a multispecies spawning site of Epinephelus fuscoguttatus and E. polyphekadion. Despite having similar abundances, E. polyphekadion was eightfold more vulnerable to capture by hook-and-line gear, clearly outcompeting its congener for bait. Contrasting with the common assumption of a proportional relationship, the CPUE of both species was unrelated to the size of their respective aggregations. Moreover, the CPUE of each species was unrelated to hook size and depth fished. However, E. polyphekadion CPUE declined as the density of fishing effort increased at the site, with gear saturation identified as the likely mechanism for this effect. E. fuscoguttatus CPUE was negatively related to the size of aggregations formed by its congener, stemming from the superior competitiveness and therefore higher selectivity of the gear for E. polyphekadion. Our findings demonstrate that CPUE is an unreliable indicator of spawning aggregation status. The other sources of variation in CPUE that we identify have implications for gear-based management, which must be based on understanding of gear selectivity for aggregating species, and fishing effort controls, which must consider the potential for effort-dependent patterns in catchability.

Item ID: 37011
Item Type: Article (Research - C1)
ISSN: 1432-0975
Keywords: spawning aggregations, catch-per-iunit-effort (CPUE), catchability, fisheries management, conservation
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A version of this publication was included as Appendix II of the following PhD thesis: Waldie, Peter Anthony (2016) Investigating spatial aspects of the community-based management of a small-scale artisanal grouper fishery. PhD thesis, James Cook University, which is available Open Access in ResearchOnline@JCU. Please see the Related URLs for access.

Funders: Australian Research Council (ARC)
Research Data: http://dx.doi.org/10.4225/28/571EB75A4DE5F
Date Deposited: 26 Apr 2016 00:55
FoR Codes: 07 AGRICULTURAL AND VETERINARY SCIENCES > 0704 Fisheries Sciences > 070403 Fisheries Management @ 100%
SEO Codes: 83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8302 Fisheries - Wild Caught > 830204 Wild Caught Fin Fish (excl. Tuna) @ 100%
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