Alaska red king crab: A relatively intractable target in a multispecies trawl survey of the eastern Bering Sea

Abstract

The success with which Alaska's groundfish stocks have been managed is not matched by management of its crab stocks, several of which have been declared overfished. It is unlikely that all species will be sampled equally well in a generic, multispecies trawl survey with a uniform distribution of sampling effort. We evaluated the relative sampling tractability of six species targeted by the eastern Bering Sea stock assessment survey conducted annually by the U.S. National Marine Fisheries Service to see if there were differences that might explain the dichotomy in management success observed for groundfish and crabs. Using relative niche breadth, Green's Index of spatial patchiness, heterogeneity of variance and abundance-estimate precision, we analyzed 22 years of survey data to conclude that three major crab species, red king crab ( Paralithodes camtschaticus), snow crab ( Chionoecetes opilio) and Tanner crab ( Chionoecetes bairdi), were less tractable than three major fish species, walleye pollock ( Theragra chalcogramma), Pacific cod ( Gadus macrocephalus) and yellowfin sole ( Pleuronectes asper). In particular, our analysis established red king crab as the species for which abundance-estimate precision, niche breadth and sampling efficiency were lowest, patchiness was highest and heterogeneity of variance was the most severe. As a consequence, Bering Sea multispecies sampling is not likely to achieve the same degree of abundance-estimation success for red king crab as it might for other crab or fish species.