Recruitment patterns of Alaskan crabs in relation to decadal shifts in climate and physical oceanography

Abstract

Crabs in Alaska support large fisheries that have been unstable because of wide fluctuations in recruitment. Data from bottom-trawl and pot surveys and commercial fisheries were used directly to derive relative recruitment series for 15 stocks of red king (Paralithodes camtschaticus), blue king (P. platypus), Tanner (Chionoecetes bairdi), and snow (C. opilio) crabs in the Gulf of Alaska, along the Aleutian Islands, and in the Bering Sea. Recruitment to most stocks is periodic and strongly autocorrelated. Year-class strength of red king crab stocks in Bristol Bay, in the northern Gulf of Alaska, and along the Aleutian Islands has similar trends and has been weak since the mid-1970s; year-class strength of Tanner crab stocks in the northern Gulf of Alaska has been weak since the early 1980s. Tanner crab recruitment patterns differ between the Bering Sea and Gulf of Alaska stocks. Recruitment trends in 7 of 15 crab stocks appear to be related to decadal climate shifts, periods of strong winter Aleutian Lows coinciding with periods of weak recruitment. Strong vertical mixing and an unstable water column associated with a strong Aleutian Low inhibits growth of Thalassiosira spp., diatoms that provide high-quality nutrition to early zoeal stages of crab larvae. Recruitment of many crab stocks may also be influenced by local conditions not indexed by the Aleutian Low. (C) 2000 International Council for the Exploration of the Sea.