Watson Jordan T, Bigelow Keith A
Joint Institute for Marine and Atmospheric Research, University of Hawaii, 1000 Pope Road, Honolulu, HI 96822, U.S.A.; University of Alaska Fairbanks, School of Fisheries and Ocean Sciences, 17109 Pt Lena Loop Road, Juneau, AK 99801, U.S.A..
Conserv Biol. 2014 Aug;28(4):1012-22. doi: 10.1111/cobi.12268. Epub 2014 Mar 14.
The interspecific preferences of fishes for different depths and habitats suggest fishers could avoid unwanted catches of some species while still effectively targeting other species. In pelagic longline fisheries, albacore (Thunnus alalunga) are often caught in relatively cooler, deeper water (>100 m) than many species of conservation concern (e.g., sea turtles, billfishes, and some sharks) that are caught in shallower water (<100 m). From 2007 to 2011, we examined the depth distributions of hooks for 1154 longline sets (3,406,946 hooks) and recorded captures by hook position on 2642 sets (7,829,498 hooks) in the American Samoa longline fishery. Twenty-three percent of hooks had a settled depth <100 m. Individuals captured in the 3 shallowest hook positions accounted for 18.3% of all bycatch. We analyzed hypothetical impacts for 25 of the most abundant species caught in the fishery by eliminating the 3 shallowest hook positions under scenarios with and without redistribution of these hooks to deeper depths. Distributions varied by species: 45.5% (n = 10) of green sea turtle (Chelonia mydas), 59.5% (n = 626) of shortbill spearfish (Tetrapturus angustirostris), 37.3% (n = 435) of silky shark (Carcharhinus falciformis), and 42.6% (n = 150) of oceanic whitetip shark (C. longimanus) were caught on the 3 shallowest hooks. Eleven percent (n = 20,435) of all tuna and 8.5% (n = 10,374) of albacore were caught on the 3 shallowest hooks. Hook elimination reduced landed value by 1.6-9.2%, and redistribution of hooks increased average annual landed value relative to the status quo by 5-11.7%. Based on these scenarios, redistribution of hooks to deeper depths may provide an economically feasible modification to longline gear that could substantially reduce bycatch for a suite of vulnerable species. Our results suggest that this method may be applicable to deep-set pelagic longline fisheries worldwide.
鱼类对不同深度和栖息地的种间偏好表明，渔民可以避免意外捕获某些物种，同时仍能有效地捕获其他物种。在远洋延绳钓渔业中，长鳍金枪鱼（Thunnus alalunga）通常被捕捞于相对较冷、较深的水域（>100米），而许多受保护的物种（如海龟、旗鱼和一些鲨鱼）则被捕捞于较浅的水域（<100米）。2007年至2011年期间，我们在美国萨摩亚延绳钓渔业中，检查了1154组延绳钓（3406946个鱼钩）的鱼钩深度分布，并记录了2642组（7829498个鱼钩）上钩位置的捕获情况。23%的鱼钩沉降深度<100米。在最浅的3个鱼钩位置捕获的个体占所有兼捕渔获物的18.3%。我们分析了在有和没有将这些鱼钩重新分配到更深深度的情况下，消除最浅的3个鱼钩位置对该渔业中捕获量最大的25个物种的假设影响。分布因物种而异：绿海龟（Chelonia mydas）的45.5%（n = 10）、尖吻四鳍旗鱼（Tetrapturus angustirostris）的59.5%（n = 626）、丝鲨（Carcharhinus falciformis）的37.3%（n = 435）和远洋白鳍鲨（C. longimanus）的42.6%（n = 150）是在最浅的3个鱼钩上捕获的。所有金枪鱼的11%（n = 20435）和长鳍金枪鱼的8.5%（n = 10374）是在最浅的3个鱼钩上捕获的。消除鱼钩使上岸价值降低了1.6 - 9.2%，将鱼钩重新分配相对于现状使平均年上岸价值提高了5 - 11.7%。基于这些情况，将鱼钩重新分配到更深深度可能为延绳钓渔具提供一种经济上可行的改进方法，从而可以大幅减少一系列易危物种的兼捕渔获量。我们的结果表明，这种方法可能适用于全球的深海远洋延绳钓渔业。
