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AFSC-Industry Cooperative Survey of Red King Crab in Nearshore Areas of Bristol Bay

red king crab
Figure 1.  Elizabeth Chilton and Dave Somerton sampling red king crab aboard the American Eagle.

RACE Division scientists Elizabeth Chilton and Dave Somerton (Fig. 1) participated in a special assessment of red king crab in the nearshore areas of Bristol Bay in cooperation with Alaska Department of Fish and Game (ADF&G) scientists Stacy Johnson-Mestre and Trent Hartill and with Scott Goodman of Natural Resources Consultants, Inc., representing the Bering Sea Fisheries Research Foundation (BSFRF).

This study, funded by the BSFRF and the NMFS National Cooperative Research Program, was motivated by the observation that Bristol Bay red king crab distribution is correlated with water temperatures in the eastern Bering Sea, with crabs migrating from cold water areas of the Bristol Bay shelf into nearshore areas with warmer waters. One potential explanation for this phenomenon is that red king crab females perform an offshore migration to release larvae and find mates, which is delayed during years with colder water temperatures due to a delay in the crab larvae development. The result would be that some portion of the mature crabs remains near shore and outside of the established survey area, affecting the availability of these crabs to the standard bottom trawl survey.

figure 2, see caption
Figure 2.  Locations of the AFSC eastern Bering Sea survey stations and stations sampled as part of the cooperative nearshore red king crab survey. The standard and nearshore survey stations included in the cooperative nearshore research area are outlined in black.

The survey was conducted aboard the chartered commercial fishing vessel American Eagle working in conjunction with the 2011 AFSC eastern Bering Sea (EBS) bottom trawl survey. The BSFRF trawl operations were of shorter duration tows (5-8 minutes) at established survey stations using a Nephrops trawl (designed to capture nearly all epibenthos in its path) for comparison to 30-minute tows with the standard 83-112 eastern otter trawl used on the EBS survey. Nine nearshore stations along the Alaska Peninsula were added to the standard EBS survey in depths ranging from 25 to 35 m while the American Eagle completed 93 tows in areas shallower than those sampled by the EBS bottom trawl survey (Fig. 2).

The sampling objectives of this research project were met by successfully coordinating the completion of bottom tows using the Nephrops trawl gear in the nearshore area of Bristol Bay as well as in the standard EBS survey area, sampling both juvenile and adult red king crab with both types of trawl gear. The final objective of comparing red king crab population abundance and distribution estimated from this survey to the red king crab abundance and distribution estimated from the AFSC standard bottom trawl survey are currently being conducted.

By Elizabeth Chilton and David Somerton

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