Replacing unintended cross-taxa conflicts with intentional tradeoffs by moving from piecemeal to integrated fisheries bycatch management
Bycatch in fisheries can have profound effects on the abundance of species with relatively low resilience to increased mortality, can alter the evolutionary characteristics and concomitant fitness of affected populations through heritable trait-based selective removals, and can affect ecosystem functions, structure and services through food web trophic links. Current piecemeal bycatch management may reduce the mortality of one taxon of conservation concern at the unintended expense of others. Bycatch mitigation measures may also reduce intraspecific genetic diversity. Examples of broadly prescribed ‘best practice’ bycatch mitigation methods that result in unintended cross-taxa conflicts are drawn from pelagic longline, tuna purse seine, gillnet and trawl fisheries. Priority improvements in data quality and in understanding ecological effects of bycatch fishing mortality to support holistic semi-quantitative and model-based ecological risk assessments of the effects of bycatch removals are identified. A transition to integrated bycatch assessment and management that comprehensively consider biodiversity across its hierarchical manifestations is needed, where relative risks and conflicts from alternative bycatch management measures are evaluated and accounted for in fisheries decision-making processes. This would enable managers to select measures with intentional and acceptable tradeoffs to best meet objectives, when conflicts are unavoidable.
Blog on Safina Center website: http://safinacenter.org/2016/03/efforts-to-save-sea-turtles-may-kill-sharks/
Program for 27 May 2018 SFP/TNC workshop on assessing and managing bycatch in longline fisheries: CLICK HERE
Presentation at FAO Regional Office for Asia and the Pacific, IATTC Bycatch Working Group, NGO Tuna Forum and SFP/TNC bycatch workshop: CLICK HERE (request presentation file with notes from EGilman@utas.edu.au)
2016. A cross-taxa assessment of pelagic longline bycatch mitigation measures: Conflicts and mutual benefits to elasmobranchs. Fish & Fisheries 17: 748-784.
Reprint of journal article: DOWNLOAD
Presentation on key findings: DOWNLOAD
TALKING POINTS
Fisheries targeting tunas and other species with high reproductive rates can have large impacts on incidentally caught bycatch species that are less productive, including seabirds, sea turtles, marine mammals, sharks and rays. Changes in gear designs and fishing practices, and other methods, can mitigate problematic bycatch. Tjere's been a lack of holistic management of fisheries bycatch to account for methods that result in tradeoffs between different at-risk species groups. As a result, bycatch measures prescribed to reduce impacts on one at-risk group - sea turtles, for example - may inadvertently exacerbate catch and mortality of another group - such as sharks.
The study presents results from a meta-analysis and literature review of the effects of pelagic longline gear elements on the catch and at-vessel survival of sharks and rays. Main findings follow:
- 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. Fishery-specific assessments are therefore warranted in order to determine relative risks.
- Interacting effects of hook, bait and leader affect shark catch rates: hook shape, hook width and bait type affect hooking position and the concomitant ability of a shark to sever monofilament leaders, when used. Because sharks caught on j-shaped hooks or fish bait tend to be hooked deeply, when monofilament nylon leaders are used, this may enable the shark to bite through the relatively weak leader and escape. When caught on circle hooks or squid bait, which tend to result in mouth hookings, sharks are unable to bite through monofilament leaders.
- Wire leaders had higher shark catch rates than monofilament leaders. This finding is timely given recent wire leader bans by some tuna RFMOs and domestic management authorities. However, leader material effect on shark fishing mortality rates is unclear. The effect of recent bans on wire leaders on shark fishing mortality rates requires improved understanding of gear factors that affect hooking position, and estimates of each component of fishing mortality (pre-catch, at-vessel, post-release) for various combinations of leader, hook and bait types.
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 modeling 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.
Media coverage
http://www.eurekalert.org/pub_releases/2016-01/w-ret012716.php
http://www.alphagalileo.org/ViewItem.aspx?ItemId=160442&CultureCode=en
http://www.wiley.com/WileyCDA/PressRelease/pressReleaseId-123124.html
ISSF blog: May 2016 on tradeoffs resulting from fisheries bycatch mitigation DOWNLOAD
March 2017, IFREMER, Sete, France http://tinyurl.com/IFREMER-Gilman