Traplines may cut sea turtle bycatch in swordfish longlines

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A newly published paper in Animals adds early evidence that traplines, a hookless modification to pelagic longline gear, may substantially reduce sea turtle bycatch in swordfish fisheries. In 23 sets conducted by a single vessel in the central Mediterranean, the researchers reported that traplines nearly eliminated turtle bycatch relative to conventional J-hooks, while still producing meaningful swordfish catch. The authors describe the results as preliminary, but the conservation signal is hard to ignore. (mdpi.com)

The study lands in a fishery management landscape that has spent years trying to make longlines less harmful to turtles rather than removing the interaction risk altogether. NOAA says pelagic longlines can injure turtles in the mouth, head, neck, flippers, or digestive tract, and entanglement can lead to lacerations, infection, drowning, or delayed death. Existing mitigation strategies, including circle hooks, finfish bait, soak-time management, and careful release tools, have reduced harm in several fisheries, but bycatch remains a persistent global problem. (fisheries.noaa.gov)

That broader context is important because traplines would represent a different kind of intervention. In Atlantic U.S. pelagic longline fisheries, federal rules already require specific sea turtle mitigation measures, including circle-hook standards, bait restrictions in some areas, and onboard handling and release guidance. In the western and central Pacific, shallow-set swordfish longline vessels are likewise required to use large circle hooks, whole finfish bait, or another approved equivalent mitigation measure. In other words, regulators already accept gear-based mitigation as a core strategy, which could make traplines a plausible candidate for future testing if stronger evidence emerges. (law.cornell.edu)

The new Animals paper is not the only recent signal in favor of the concept. An ICCAT working paper assessing trapline use in the western Mediterranean reported lower catches of endangered, threatened, and protected species in trapline sets than in traditional hook sets, while recommending expanded experimental trials under scientific monitoring. That analysis also flagged open questions, including whether traplines work best when attached directly to the mainline or incorporated into branchlines, and how they affect selectivity and gear performance across conditions. (iccat.int)

The larger bycatch literature suggests why fisheries scientists may pay attention. NOAA and WCPFC both point to strong evidence that large circle hooks and finfish bait can significantly reduce turtle hooking, and prior studies in the Atlantic, Azores, Sicily, and Hawaii have reported meaningful reductions in turtle bycatch with those modifications. But those measures still involve baited hooks. Traplines are drawing interest because, at least in these early reports, they may reduce the chance of a turtle being hooked in the first place, which is a more direct welfare and survival gain. (fisheries.noaa.gov)

Why it matters: For veterinarians working in marine wildlife medicine, rehabilitation, and population health, this is a prevention story as much as a fisheries story. Longline-caught turtles often require triage for penetrating trauma, entanglement injuries, aspiration risk, stress, and post-release uncertainty. A gear change that reduces capture events upstream could lower caseloads, improve survival odds, and reduce the clinical burden associated with dehooking, imaging, surgery, wound care, and long rehabilitation stays. It also aligns with a One Health-style view of conservation medicine, where better fishery design can be as important as better treatment protocols once an animal is already injured. (fisheries.noaa.gov)

There are still reasons to be cautious. The Animals study was based on a small number of sets and one vessel, and the ICCAT paper suggests traplines may change catch composition and size selectivity in ways that need closer evaluation. Wider adoption will likely depend on whether larger trials can confirm turtle benefits without unacceptable losses in target catch, operational efficiency, or safety. Expert reaction in formal commentary appears limited so far, but the direction of travel in the literature is consistent: promising small-scale bycatch innovations need robust field validation before they can move into policy or fleet-wide recommendations. (mdpi.com)

What to watch: The next step is more monitored, multi-vessel testing, especially in fisheries where turtle bycatch remains high and regulators already recognize equivalent gear-based mitigation pathways. If the early Mediterranean results hold up, traplines could move from an intriguing niche modification to a serious candidate in future bycatch policy discussions. (iccat.int)