742 



Fishery Bulletin 102(4) 



61 "N- 



60 N- 



59 N- 



58 N- 



57°N- 



56N- 



55N- 



54N- 



166 W 



164 = W 



162 W 



160 W 



158 W 



Figure 2 



The annual eastern Bering Sea survey station grid showing the 

 number of successful tows per station block made during the 2002 

 red king crab capture efficiency study. Each block represents a 

 400-nmi 2 area. 



codend with a 3.1-cm stretch mesh liner. The 38.2 m long 

 auxiliary footrope constructed of heavy 16-mm-long link 

 trawl chain was designed to drag through soft bottom 

 and presumably captures all escaping crabs. Munro and 

 Somerton (2002) provided detailed construction plans of 

 this experimental gear in their appendices. 



Experimental design 



Operations were conducted from 21 to 29 July 2002, 

 aboard the FV Arcturus, one of two commercial stern 

 trawlers chartered by the AFSC since 1993 to carry 

 out annual Bering Sea groundfish surveys. Trawling 

 took place in Bristol Bay (Fig. 2) at depths from 41 to 

 77 m and followed standardized survey protocols that 

 included towing during daylight hours at a 1.5 m/sec (3 

 knots) vessel speed and using locked winches and stan- 

 dardized lengths of trawl warp (scope) at each towing 

 depth. Acoustic net mensuration equipment was used 



to measure wing spread for each tow. Bottom contact 

 sensors were used on the centers of both the trawl and 

 auxiliary footropes to measure the distance (in centime- 

 ters) between the footropes and the bottom (Somerton 

 and Weinberg. 2001). A silicon-intensified tube (SIT) 

 camera, which uses ambient light, was attached to the 

 center of the trawl to view RKC interaction with the 

 footrope. On some of our trial tows, however, a 30-W 

 quartz halogen light was also used to increase contrast 

 between ambient light and the sea floor. 



Two departures from standardized survey protocol 

 were necessary for this experiment. First. 27.5-m long 

 bridles were used instead of the survey standard 55- 

 m long bridles to help offset the loss of wing spread 

 caused by the added drag of the auxiliary net (Munro 

 and Somerton, 2002). Second, tow length was shortened 

 from the survey standard of 30 min to 20 min to mini- 

 mize the decrease of path width over time due to in- 

 creased drag from large catches in the auxiliary net. 



