746 



Fishery Bulletin 102(4) 



in the current management model for male maturity); 

 84.1% at 135 mm (legal size for males); and 92.7% at 

 184 mm (size of the largest male crab encountered in 



O 



50 100 150 



Carapace length (mm) 



Figure 4 



A 2-parameter logistic model (solid line) and 959S confi- 

 dence bounds idashed lines) estimating male red king crab 

 capture probability for the 83/112 Eastern survey bottom 

 trawl. Symbols are scaled to the sample length frequency 

 summed over all tows and binned into 5-mm carapace length 

 intervals. Symbols range in size from the smallest circle 

 representing a single individual to the largest circle repre- 

 senting 138 males. 



1 n 



0.8- 



o 



o. 0.6 







0.4 



0.2 



50 100 150 



Carapace length (mm) 



Figure 5 



A 2-parameter logistic model isolid line) and 959! confi- 

 dence bounds idashed linesl estimating female red king crab 

 capture probability for the 83/112 Eastern survey bottom 

 trawl. Symbols are scaled to the sample length frequency 

 summed over all tows and binned into 5-mm carapace length 

 intervals. Symbols range in size from the smallest circle 

 representing two individuals to the largest circle represent- 

 ing 206 females. 



our experiment [Fig. 4]). The fitted model predicted 

 female capture probability to be 65.27c at 51 mm (size 

 of the smallest female observed); 69.8% at 90 mm (size 

 at which both full vulnerability to the survey trawl 

 and 50% female maturity are assigned in the cur- 

 rent management model); 74.7% at 135 mm (same 

 size at which males enter the fishery); and 77.4% 

 at 162 mm (size of the largest female crab encoun- 

 tered in our experiment [Fig. 5]). Estimated capture 

 probability for both male and female crab was equal 

 at 88 mm (69.9%). Model variability, as indicated 

 by the 95% confidence bounds, was greatest at the 

 extremes of our size ranges because of low sample 

 frequency. This was especially true for small crabs, 

 and the uncertainty was so large that extrapolation 

 of the capture probability functions to either males 

 or females below <60 mm is not recommended. 



Factors influencing escapement 



Modeling the effect of various factors on capture 

 probability was based on observations of RKC 

 (ra=248) from videotapes collected during 28 EBS 

 tows. Approximately two-thirds of the counted crabs 

 were captured. The influence of artificial lighting, 

 body height, footrope distance from the bottom, 

 crab size, body orientation, and the interaction of 

 body height and body orientation were significant 

 (Table 3). Capture probability decreased when lights 

 were used and when the distance between the foot- 

 rope and the bottom increased. Capture probability 

 increased when crabs were standing up on their 

 legs, with increased body size, and when the footrope 

 contact was made along the body axis rather than 

 from the side of the crab. 



Capture probability, based on direct observation, 

 was predicted by the fitted logistic models to illus- 

 trate how the various explanatory variables affect 

 the capture outcome. We present two examples. In 

 the first case, capture probability in natural light 



