142 



Fishery Bulletin 89(1), 1991 



where n is the number of observations, and D ; is the 

 linear displacement after t; days for crab i. When our 

 best measurement for any Dj was zero, we assumed a 

 minimum Dj of lm so that Equation (6) was defined 

 for all data points i = l,...,n. Our Equation (6) is the 

 maximum-likelihood solution to Equation (3) of Skellam 

 (1951), or Equation (11.6) of Pielou (1977), both of 

 whom develop a mathematical framework for describ- 

 ing random dispersal of individuals from a release 

 point. As for our analysis of movement and mortality, 

 f 2 was minimized and approximate standard errors 

 for A were determined using Mittertreiner and 

 Schnute's (1985) SIMPLEX package. 



Results 



Beam-trawl and trap sampling 



Beam-trawl surveys in 1985 and 1986 captured few 

 Dungeness crabs except in the selected locations con- 

 sidered in the following paragraphs. In 46 beam trawl 

 samples, 2- to 3-year-old (=75- 145 mm CW) male and 

 female crabs (Butler 1961, Stevens and Armstrong 

 1984, Smith and Jamieson 1989c) were found at den- 

 sities generally less than 10/hectare (ha). Where much 

 higher densities were found, there were significant 

 seasonal differences, and differences in the relative pro- 

 portions of males and females. Sampling since 1986 in 

 the same locations (G. Jamieson, unpubl. data) has in- 

 dicated that the overall abundance of crabs in the 

 75-145 mm CW size range has dropped to a low level, 

 thus we believe the pattern of spatial and temporal 

 distribution we describe herein is based on observations 

 of essentially one strong year-class. 



In upper Lemmens Inlet the densities of male and 

 female 2-year-olds in summer 1985 were initially low 

 and continued to decline throughout 1985 and 1986 

 (Fig. 3a). This suggests this area is a poor crab habitat 

 since this cohort was abundant elsewhere. The highest 

 density of males was observed in middle Lemmens In- 

 let (Fig. 3b). During autumn 1985 and the subsequent 

 winter, male densities steadily increased to greater 

 than 1200/ ha. Toward the mouth of Lemmens Inlet 

 male densities generally declined (Fig. 3c, d). Because 

 densities of 2-year-old males elsewhere were con- 

 sistently low, the increase in the number of males in 

 middle Lemmens Inlet is suspected to be due to move- 

 ment away from exposed shallow water during winter. 



We suspect that these males concentrated in middle 

 Lemmens Inlet because of poor habitat further up the 

 inlet. This high density of males eventually decreased 

 rapidly during late spring 1986. Most males were in 

 the normally distributed instar with a mean carapace 

 width of 129 mm and a standard deviation of 12 mm 

 (Smith and Jamieson 1989c), and many molted to legal 



UPPER LEMMENS INLET 



300' 



in 







£- 

 ui 

 Q 900 



MIDDLE LEMMENS INLET 



 MALE 

 • FEMALE 



( 75-l45mm CW ) 



1 1 1 1 1 — I 1 1 1 1 1 1 1 — r I I 



LOWER LEMMENS INLET 



CO 



600 



300 





 600 



300- 



~1 I I I I T I I 

 ENTRANCE TO LEMMENS INLET 



t i i — i — i — i — i — i — i — i — i — i — rn — I -\ 



MAIN CHANNEL 



1 1 "T I I 1 I I I I 1 I I 1 1 1 1 1 



M J J A SON D|JFMAMJ J A S 



1986 

 DATE 



1985 



Figure 3 



Time-series of densities for 2-3 year-old (=75-145 mm CW) 

 male and female Dungeness crabs in upper Lemmens Inlet 

 (zone 1), middle Lemmens Inlet (zone 2), lower Lemmens In- 

 let (zone 2), the entrance to Lemmens Inlet (zone 3), and in 

 the main channel out to sea (zone 6). 



size in 1986 (i.e., to the normally distributed instar with 

 a mean carapace width of 156 mm and a standard devia- 

 tion of 13 mm). Following their molt to legal size they 

 were quickly caught in an intense fishery (Smith and 

 Jamieson 1989b). About 25-35% of the fishing effort 

 in the study site was concentrated in Lemmens Inlet 

 during spring 1986 (Fig. 2b). 



A high density of 2-year-old females was observed 

 in the narrow channel at the lower end of Lemmens 

 Inlet in June 1985 (Fig. 3c). Density declined after this 

 date, but increased during autumn in the entrance to 

 Lemmens Inlet (Fig. 3d) 0.5-1. Okm seaward of the nar- 

 row channel. Female density further up Lemmens 



