Stevens: Survival of king and tanner crabs captured incidentally in the Bering Sea 



737 



■g 2.0 



0) 



o 



^ .a 



0) 



> 



3 1.0 



g 



< 0.5 



IMMEDIATE 81.63 " 



DELAYED 0.60 ns 



SHELL CONDITION 



Figure 4 



Effects of shell condition on immediate and delayed survival odds 

 of king crabs. Condition coded as 1 = soft, 2 = new hardshell, 3 = old 

 hardshell. Immediate effects are weighted by sample factors, delayed 

 effects are not. *** indicates X- value significant at p<0.001. 

 Sample size indicated above bars. 



CO 



4) 



a 



E 



^ 0.. 



KING CRAB 



TANNER CRAB 



61-75 76-90 91-105 106-120 121-135 136-150 



CARAPACE SIZE (mm) 



3 



> 

 O 



KING CRAB 



61-75 76-90 91-105 106-120 121-135 136-150 



CARAPACE LENGTH (mm) 



Figure 5 



Effects of size on survival. (A) Immediate survival of king and Tan- 

 ner crabs by 15-mm intervals of carapace length (king crabs) or 

 carapace width (Tanner crabs). Numbers represented by each interval 

 are 226-1520 king crabs and 71-9752 Tanner crabs. (B) Overall 

 survival of king crabs, calculated as the product of immediate and 

 delayed survival estimates. 



LU 



CI 



C2 



PAN 



CHU 



STD 



C1 



02 



PAN 



CHU 



STD 



0.2 0.4 0.6 



IMMEDIATE SURVIVAL 



Figure 6 



Effect of gear type on immediate survival of king and Tanner crabs. 

 Vertical bar represents the mean; outer ends of box represent up- 

 per and lower confidence intervals, defined as 1.96(pq/n)"". 



All female and most male Tanner crabs were har(i- 

 shell (condition 2). Less than 0.3% of males were old- 

 shell (condition 3), and less than 0.01% were softshell 

 (condition 1). Low incidence of softshell and oldshell 

 Tanner crabs prevented contingency table analysis due 

 to too many empty cells. 



Size effects 



Immediate survival of king crabs did not vary much 

 over the range of sizes captured (Fig. 5A). For Tan- 

 ner crab, however, immediate survival increased slight- 

 ly with size. Overall survival of king crabs (Fig. 5B) 

 decreased markedly at sizes above 120 mm CL, most- 

 ly as a result of increased delayed mortality. Delayed 

 mortality and overall survival could not be determined 

 for Tanner crabs because of the limited number of 

 observations. 



Effects of gear type 



Since survival was strongly related to CAPTIME, an 

 analysis of variance was performed to determine if 

 CAPTIME differed between the nets used. No signifi- 

 cant differences were found (F = 0.570, a = 0.685, df = 

 4181), so any differences in survival between nets can 

 be attributed directly to the nets. 



Immediate survival was least for the standard net 

 (STD), for both species (Fig. 6). Nets C2 and CHU pro- 

 duced the best survival for king crabs, whereas CI and 

 PAN produced better survival for Tanner crabs. 

 Overall, the experimental nets produced no clear dif- 

 ferences in survival from the control nets for either 

 species of crab. Extremely poor survival of Tanner 

 crabs occurred in the standard net, and was probably 

 the result of a biased vitality sample, which included 



