Terra Daily: Fish and marine species are among the most threatened wildlife on earth, due partly to over exploitation by fishing fleets. Yet there are differences in assessing trends in worldwide fishing stocks which, researchers writing in Conservation Biology argue, stem from inappropriate use of time trends in catches."Estimates of fishery status based on catches suggest that around 30% of fisheries are collapsed and 70% are overexploited or collapsed," said lead author Dr Trevor Branch from the University of Washington in Seattle. "Our assessment shows that the data are seriously biased, and that instead we should be looking at biomass data."
Biomass data from scientific stock assessments indicated a much smaller proportion in these categories (12% collapsed, 26% overexploited or collapsed), and that status trends are stable. Dr Branch's analysis suggests that in most regions fisheries management has led to stabilization, and even recovery, of fished populations.
"Species which are targeted by fishing fleets are divided into stocks, a division of species into units based on political boundaries, genetic divergence, and biological characteristics," said Branch. "The depletion of these stocks has important implications for ecosystem biodiversity; however methods of measuring depletion vary greatly."
Dr Branch's team considered stocks being "collapsed" or "overexploited" on the basis of catch and biomass data. Collapse is defined as biomass of less than 10% of unfished levels while over exploitation is defined by the governments of the United States and Australia as biomass below 50% of biomass that would produce maximum sustained catches. These reference points are widely used in fisheries management, either as management targets or as limits not to be exceeded….
Fish in net, shot by Joseolgon, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license
No comments:
Post a Comment