False killer whales are the most frequently-recorded bycaught cetacean in the Hawai‘i-based deep-set longline fishery. Observer coverage averaged ~20% from 2000-2019, and mortality and serious injury (M&SI) rates calculated from observed interactions (i.e., hooking or entanglement) are extrapolated to unobserved effort to determine overall bycatch estimates. These estimates routinely exceed the Potential Biological Removal level for the Hawai‘i pelagic stock, and in 2010 a Take Reduction Team (TRT) was established. A Take Reduction Plan (TRP) in 2013 included both gear changes (i.e., “weak” circle hooks (≤4.5mm wire diameter) and “strong” branchlines (≥2.0mm diameter)) and handling guidelines, to put tension on the gear to straighten hooks and release individuals alive without gear attached. Since 2013, overall effort has increased, as have interaction rates and overall bycatch estimates. Based on observed trips, crew often fail to put tension on gear, and in 75.3% of cases branchlines break or are cut, releasing hooked animals with trailing gear, typically classified as “serious injuries” (i.e., having a >50% likelihood of mortality). In 2023 the industry voluntarily began distributing a “fighting line device” meant to improve handling of hooked individuals for the purposes of removing gear, although no cases of its use with false killer whales have yet been reported. Observer coverage in the fishery declined to 15% in 2023 and is expected to decline to 13% in 2024. Given the potential for an observer effect, on unobserved trips handling guidelines are less likely to be followed, invalidating extrapolation of observed M&SI rates to unobserved effort. Electronic monitoring (EM) in 100% of the fishery would both help incentivize crew to follow handling guidelines, and provide a basis for assessing effectiveness and compliance. In March 2023, there was a consensus recommendation from the TRT that EM be implemented fleet-wide, but to date no action has been taken.
Citation:
Baird, R.W. 2024. The Perils of Relying on Handling Techniques to Reduce Bycatch in a Partially Observed Fishery: A Fatal Flaw in the U.S. False Killer Whale Take Reduction Plan. Document SC/69B/SM/11 submitted to the International Whaling Commission Scientific Committee, Bled, Slovenia.
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