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Shellfish Assessment Program - Kodiak Laboratory

Annual Eastern Bering Sea Continental Shelf Bottom Trawl Survey: Crab

measuring crab
Figure 1.  Scientists (Joel Webb, Duane Stevenson, Nancy Roberson, Claire Armistead, Jay Clark, Jason Conner) measuring crab caught in a Tanner and red king crab hot spot tow.  Photo courtesy of Nick Malahovsky.
 
 

The 2008 eastern Bering Sea bottom trawl survey conducted by the Groundfish and Shellfish Assessment Programs took place from 4 June to 24 July aboard the chartered fishing vessels Aldebaran and Arcturus (Fig. 1). Three hundred seventy-five standard stations were sampled starting from Bristol Bay and moving west past St. Matthew Island on the Bering Sea shelf. In addition, three extra stations were sampled after encountering a Paralithodes camtschaticus (red king crab) and Chionoecetes bairdi (Tanner crab) “hot spot,” defined as 100 or more legal-sized males.

Over 50,000 individual crab of five commercially important species, including red king crab, P. platypus (blue king crab), C. opilio (snow crab), Tanner crab and Erimacrus isenbeckii (hair crab) were measured, and other biometric data such as shell and egg condition, weight, chela height, and presence of parasitism were recorded. Several special studies were conducted in addition to the assessment, including reproductive potential of snow and red king crab, hemolymph collections from Chionoecetes spp. to monitor bitter crab syndrome, and population genetics studies of Paralithodes spp.

For the third time in as many years, after the majority of the standard stations were completed, one of the vessels returned to Bristol Bay to resample predetermined stations for red king crab. (See EBS groundfish survey summary, page 13.) Many of the mature female red king crab caught at the beginning of the survey had not extruded new clutches of eggs due to cold water temperatures. Because spawning stock assessment models rely upon future recruitment and mating success, the delay of the new clutches necessitated the return to Bristol Bay. At the time of the resampling, 99% of mature females had completed the mating and molting cycle and extruded new clutches.

Station locations and numbers of legal male red king crab, Tanner crab, and snow crab caught per square nautical mile are distributed in Bristol Bay and along the Bering Sea shelf. Due to low stock abundance, the fishery for blue king crab in the Pribilof District has been closed since 1999 and in the St. Matthew District since 1998. The red king crab fishery in the Pribilof District has also remained closed due to blue king crab bycatch concerns. Historically there was a fishery for hair crab, although there has not been one since 2000.


Table 1.  The 2007 and 2008 abundance estimates (± 95% confidence interval) for legal and preferred sized males (millions of crab) of commercial crab stocks in the eastern Bering Sea.
 
Stock 2008 2007
Bristol Bay District red king crab 10.5 ± 3.1 13.3 ± 5.3
Pribilof District red king crab 1.2 ± 1.1 1.6 ± 1.3
Pribilof District blue king crab 0.02 ± 0.04 0.11 ± 0.08
St. Matthew Island Section blue king crab 1.7 ± 0.9 1.4 ± 0.9
Tanner crab, all districts 13.2 ± 7.4 12.1 ± 6.8
Snow crab, all districts 368.6 ± 75.9 495.2 ± 134.8
Snow crab, all districts > 4.0 inches 119.7 ± 27.5 150.9 ± 61.6
Hair crab, all districts 2.3 ± 1.1 2.0 ± 0.8


The 2008 abundance estimates for the five commercial crab species relative to the 2007 survey results showed a decrease in survey abundance in many stocks (Table 1 above). The 2008 abundance estimates for prerecruit male and females showed variable results compared to recent trends but are characterized by a large amount of uncertainty. These data and additional station information are available in the NOAA Technical Memorandum The 2008 Eastern Bering Sea Continental Shelf Bottom Trawl Survey: Results for Commercial Crab Species. The publication is posted on the AFSC website at http://www.afsc.noaa.gov/Publications/AFSC-TM/NOAA-TM-AFSC-187.pdf.

By Jan Haaga, Liz Chilton, and Claire Armistead
 

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