Two devices for mitigating odontocete bycatch and depredation at the hook in tropical pelagic longline fisheries

摘要: Odontocete bycatch on and depredation from tropical pelagic longlines is globally widespread, having negative impacts the economic viability of affected fisheries conservation odontocete populations. Reports by fishers that depredating odontocetes avoid gear tangles has underpinned development simulated structures to physically deter odontocetes. This study assessed efficacy two such devices developed mitigate associated bycatch. Of particular interest was their impact (i) soak depth (ii) sink rate using truncated trials, before determining under full operational conditions rates (iii) catch five most economically important fish, (iv) bycatch, changes in (v) fish survival size, (vi) setting hauling speed. The results indicated inclusion had negligible depth, thus were unlikely suite specifically targeted caught. slowed, perhaps drag, trapped air, or propeller wash, although addition weight might remedy this if be used areas where seabird could occur. Most importantly, trials conducted Australian Fijian waters pooled (i.e. albacore, yellowfin, bigeye, mahi mahi, wahoo) increased presence devices, possibly because more attracted them depredators deterred. Catch control next with attached higher than distant gear, suggesting influences may have extended adjacent branchlines. size caught mostly unaffected, yellowfin bigeye significantly devices. Hauling slowed use need for an extra crewmember during hauling, which cost prohibitive some fisheries, especially benefits are not obvious. Despite small sample only occurred unprotected fishing all individuals released alive, fate uncertain; there evidence injuries sustained event. outcomes positive should motivate stakeholders view as a potentially effective tool mitigating similar longline fisheries. Future efforts focus improving integration reducing implementation costs encourage voluntary uptake non-compliance costly monitoring. technology bring about marked improvements situation populations