School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, WA 98195-5020, USA.
Conserv Biol. 2009 Jun;23(3):626-35. doi: 10.1111/j.1523-1739.2008.01121.x. Epub 2008 Nov 18.
Bycatch--the incidental catch of nontarget species--is a principal concern in marine conservation and fisheries management. In the eastern Pacific Ocean tuna fishery, a large fraction of nonmammal bycatch is captured by purse-seine gear when nets are deployed around floating objects. We examined the spatial distribution of a dominant species in this fishery's bycatch, the apex predator silky shark (Carcharhinus falciformis), from 1994 to 2005 to determine whether spatial closures, areas where fishing is prohibited, might effectively reduce the bycatch of this species. We then identified candidate locations for fishery closures that specifically considered the trade-off between bycatch reduction and the loss of tuna catch and evaluated ancillary conservation benefits to less commonly captured taxa. Smoothed spatial distributions of silky shark bycatch did not indicate persistent small areas of especially high bycatch for any size class of shark over the 12-year period. Nevertheless, bycatch of small silky sharks (<90 cm total length) was consistently higher north of the equator during all years. On the basis of this distribution, we evaluated nearly 100 candidate closure areas between 5°N and 15°N that could have reduced, by as much as 33%, the total silky shark bycatch while compromising only 12% of the tuna catch. Although silky sharks are the predominant species of elasmobranchs caught as bycatch in this fishery, closures also suggested reductions in the bycatch of other vulnerable taxa, including other shark species and turtles. Our technique provides an effective method with which to balance the costs and benefits of conservation in fisheries management. Spatial closures are a viable management tool, but implementation should be preceded by careful consideration of the consequences of fishing reallocation.
副渔获物——即非目标物种的意外捕获物——是海洋保护和渔业管理的主要关注点。在东太平洋金枪鱼渔业中，当渔网围绕漂浮物部署时，大量非哺乳动物副渔获物被围网渔具捕获。我们研究了该渔业副渔获物中占主导地位的物种——顶级掠食者丝鲨（Carcharhinus falciformis）的空间分布，以确定空间关闭（即禁止捕鱼的区域）是否可以有效减少该物种的副渔获物。然后，我们确定了渔业关闭的候选地点，这些地点特别考虑了减少副渔获物与金枪鱼捕捞损失之间的权衡，并评估了对不太常见捕捞类群的附带保护益处。在 12 年的时间里，丝鲨副渔获物的平滑空间分布并未表明任何大小类别的鲨鱼存在特别高的副渔获物的持久小区域。尽管如此，在所有年份中，赤道以北的小丝鲨（全长<90 厘米）的副渔获物始终较高。基于这种分布，我们评估了近 100 个候选关闭区域，这些区域位于 5°N 至 15°N 之间，可以将总丝鲨副渔获物减少多达 33%，而仅影响 12%的金枪鱼捕捞量。虽然丝鲨是该渔业中被副渔获的主要软骨鱼类，但关闭区域也表明了其他脆弱类群（包括其他鲨鱼物种和海龟）的副渔获物减少。我们的技术提供了一种在渔业管理中平衡保护成本和收益的有效方法。空间关闭是一种可行的管理工具，但在实施之前，应仔细考虑重新分配捕捞的后果。
