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The Effect of Terminal Gear Modifications on the Total Mortality of the Shortfin Mako, Isurus oxyrinchus
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2021
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Series: PIFSC working paper ; WP-21-004
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Description:Due to the overfished status of the North Atlantic shortfin mako, Isurus oxyrinchus, ICCAT has identified the need to better understand the effect of terminal gear modification as a mitigation measure in longline fisheries. Here we update two meta-analyses as one of the referenced studies was found to have a confounding variable that resulted in interpreting a bait effect as a hook effect. In both cases, significant differences in catchability are lost between hook types. For at-haulback mortality, the cited sources from the two meta-analyses were combined to maximize sample size; an updated model demonstrates a significant reduction of 10% in at-haulback mortality due to circle hook use relative to J-hook use. In review of additional publications, shortfin mako caught with circle hooks vs. J-hooks were twice as likely to be mouth hooked vs. foul or gut hooked, with the latter two being at least 4.5 times more lethal than mouth hooking. Overall, our paper demonstrates circle hook use is effective for reducing total mortality of the species and improves the probability of survival of shortfin mako incidentally captured in longlining fishing operations.
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Rights Information:Public Domain
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Compliance:Submitted
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