Abstract.- King crabs Parali- 

 thodes camtschaticus and Tanner 

 crabs Chionoecetes bairdi captured 

 incidentally by Bering Sea trawlers 

 were examined for immediate mor- 

 tality, vitality, and injuries resulting 

 from ti'awl capture. A number were 

 held aboard ship for 2 days in sea- 

 water to determine delayed mortal- 

 ity. Overall survival, including imme- 

 diate and delayed effects, was 21% 

 (±2.0%) for king crabs and 22% 

 (±3.6%) for Tanner crabs. Immedi- 

 ate mortality of king crabs decreased 

 significantly with shell age, and in- 

 creased significantly with time in 

 captivity prior to assessment, from 

 0% at 3 hours to 100% at 17 hours. 

 Vitality, an index of spontaneous ac- 

 tivity level, was a better predictor of 

 delayed mortality than was the pres- 

 ence/absence of injuries. The effect 

 of leg and body injuries on mortal- 

 ity of king crabs was similar, but in- 

 juries to leg segments proximal to 

 the plane of autotomy resulted in 

 higher mortality than injuries distal 

 to the autotomy plane, or autotom- 

 ization alone. 



Survival of King and Tanner Crabs 

 Captured by Commercial Sole Trawls 



Bradley G. Stevens 



Kodiak Laboratory, Alaska Fisheries Science Center 



National Marine Fishenes Service, NOAA, PO Box 1638, Kodiak. Alaska 99615 



Manuscript accepted 31 .hily I'.lltO. 

 Fishery Bulletin, U.S. 88:7.31-744. 



Capture and subsequent mortality of 

 nontarget (bycatch) species is a major 

 problem facing managers of multi- 

 species fisheries. In the U.S. eastern 

 Bering Sea (EBS), joint-venture (JV) 

 trawl fisheries targeting on yellowfin 

 sole Limanda aspera, rock sole Lepi- 

 dopsetta hilineata, and Pacific cod 

 Gadus macrocephalus, routinely 

 catch red king crabs Paralifhodes 

 camtschaticus and Tanner crabs Cli i- 

 onoecetes bairdi and C. opilio. In 

 1988, 88000 red king crabs, 751000 

 C. bairdi, and 2.4 million C. opilio 

 were captured in 1.30 million metric 

 tons (t) of groundfish by JV fishing 

 vessels, representing catch rates of 

 0.07, 0.58, and 1.84 crabs/t, respec- 

 tively (Berger and Weikart 1989). 

 Additional quantities of these crab 

 species were also captured by domes- 

 tic fishermen, but their numbers are 

 unknown due to the absence of an 

 effective domestic fishery observer 

 program. All three species of crab 

 are designated as 'Prohibited species' 

 by the North Pacific Fishery Manage- 

 ment Council (NPFMC), and must be 

 returned to sea. Nonetheless, mor- 

 tality of incidentally caught crab is 

 considered to be 100%, and repre- 

 sents losses from the directed crab 

 fisheries. 



Due to concerns expressed by crab 

 fishermen about the effects of by- 

 catch on crab populations, a portion 

 of the EBS was closed to trawling by 

 the NPFMC in 1986 to protect king 

 crabs, and has remained closed to 

 date. In addition, maximum catch 

 rates (crabs/t) and caps on total crab 

 catch have been defined for particu- 

 lar regions of the EBS. Somerton 

 and June (1984) attempted to quan- 



tify the relative costs to the crab fish- 

 ery and benefits to the trawl fishery 

 from conducting trawl fisheries on 

 crab grounds, in order to designate 

 those areas with negative relative 

 costs as a king crab conservation 

 zone, but their recommendations 

 were never implemented per se. 



The establishment of caps and max- 

 imum allowable catch rates was pred- 

 icated on the assumption that all 

 crabs captured incidentally to trawl 

 fisheries subsequently die. However, 

 this is not necessarily the case. In 

 August of 1988, the opportunity 

 arose to conduct an experiment to 

 determine the survival rate of crab 

 caught incidentally by the JV trawl 

 fishery. This was conducted in con- 

 junction with a study to determine 

 the effectiveness of experimental 

 nets designed to reduce the bycatch 

 of crab. The goals of the study were 

 to determine immediate and delayed 

 survival and mortality of crabs, and 

 the effects on survival of injuries, size 

 and shell age of crabs, processing 

 time, and gear (trawl) type. 



Materials and methods 



Definitions 



The term survival (S), as used in this 

 report, means the proportion of a 

 given group of crabs which was alive 

 at a specified time. Mortality (M) is 

 the complement of this value, i.e., 

 1 - S. In this investigation, survival 

 was treated as a two-step process; 

 immediate survival (ISURV) or mor- 

 tality (IMORT) is the proportion de- 

 termined to be alive or dead, respec- 

 tively, when the crabs were first 



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