Abstract. - We studied move- 

 ment of Dungeness crab Cancer ma- 

 gister near Tofino, British Columbia 

 using four methodologies. By the first 

 two methods, beam trawling and trap 

 sampling at specific locations, we in- 

 ferred that males retreated to deeper 

 water in winter and returned to shal- 

 lower water in spring. Maturing fe- 

 males tended to move from coastal 

 inlets to the more exposed coast. By 

 the third method, a simultaneous anal- 

 ysis of crab movement and mortal- 

 ity using mark-recovery and fishing- 

 effort data, we showed that dispersal 

 was not extensive. Although insen- 

 sitive to seasonal movement patterns, 

 results of this analysis suggested a 

 pattern of female movement consis- 

 tent with that inferred from the beam 

 trawl and trap data. By the fourth 

 method, acoustic tagging, we learned 

 that crab movement rates are incon- 

 sistent, having observed both large 

 daily displacements (up to 925 m/day) 

 and days of no discernible move- 

 ment. The latter two analyses sug- 

 gested that females tended to move 

 about more than males, with the 

 acoustic tagging results indicating 

 less movement by both sexes during 

 winter. Annual instantaneous total 

 mortality, which is composed pre- 

 dominantly of natural mortality, for 

 tagged sublegal-sized males was esti- 

 mated at 2.5 (95% CI of 2.3-2.8). 

 This is moderately less than our 

 original natural mortality estimate of 

 2.9-4.5 and confirms that this orig- 

 inal estimate was not grossly aber- 

 rant due to the confounding of move- 

 ment with mortality. We estimated 

 annual instantaneous total female 

 mortality, which is also composed 

 predominantly of natural mortality, 

 to be considerably lower than that of 

 males at 1.3 (95% CI of 0.8-1.8). 



Movement, Spatial Distribution, 

 and Mortality of Male and Female 

 Dungeness Crab Cancer magister 

 near Tofino, British Columbia 



Barry D. Smith 



Glen S. Jamieson 



Department of Fisheries and Oceans, Biological Sciences Branch 

 Pacific Biological Station. Nanaimo, British Columbia V9R 5K6. Canada 



Manuscript accepted 17 October 1990. 

 Fishery Bulletin, U.S. 89:137-148 (1991). 



The Dungeness crab Cancer magister 

 is fished commercially from Alaska to 

 central California along the Pacific 

 coast of North America. For at least 

 four decades this highly valued spe- 

 cies has undergone dramatic cyclical 

 fluctuations in commercial landings, 

 and coincidently in population abun- 

 dance (Methot and Botsford 1982), 

 along the Pacific coast from northern 

 California to Washington. These fluc- 

 tuations have had undesirable eco- 

 nomic consequences (Botsford et al. 

 1983) and potentially could result 

 in serious biological consequences 

 (Botsford and Wickham 1978, McKel- 

 vey et al. 1980). Therefore, there has 

 been considerable research focused 

 on developing an understanding of 

 this phenomenon in recent years 

 (Botsford 1986). Studies of this in- 

 triguing problem have been pursued 

 methodically, with competing hypoth- 

 eses systematically being eliminated 

 (Botsford 1986). However, Methot 

 (1986) points out that our understand- 

 ing of Dungeness crab population 

 dynamics is still limited by a lack of 

 information on basic population pro- 

 cesses such as growth, mortality, 

 movement, and reproduction. 



Studies of basic processes serve 

 three purposes. Firstly, new informa- 

 tion helps us develop a more complete 

 understanding of complex processes. 

 Inobvious gaps in our understanding 

 of complex processes can cause frus- 

 trating failures to explain observed 

 phenomena. Secondly, population 



models will be more realistic when 

 supported by confident parameter 

 estimates for key rate variables of 

 processes generally understood. 

 Thirdly, many studies yield data and 

 information for which there are com- 

 peting explanations, and further re- 

 search is required to resolve the hy- 

 potheses in competition. A relevant 

 example is our estimate of male Dun- 

 geness crab mortality (Smith and 

 Jamieson 1989b) for which move- 

 ment from the study site was an 

 alternate explanation for the disap- 

 pearance of tagged crabs. 



The primary purpose of this paper 

 is to report some recent progress 

 toward understanding the movement 

 and spatial distributions of male and 

 female Dungeness crab. Dungeness 

 crab population dynamics were 

 studied near Tofino, British Colum- 

 bia, where a productive regional crab 

 fishery has existed for a number of 

 decades. This site has been a focal 

 point for Dungeness crab studies in 

 British Columbia since 1985 (Jamie- 

 son and Phillips 1988, Smith and 

 Jamieson 1989a, b,c). In addition to 

 our studies of movement and spatial 

 distributions, we estimated male and 

 female mortality from a simultaneous 

 analysis of movement and mortality 

 of tagged crabs. The experimental 

 design addressed the problem of 

 movement and mortality being con- 

 founded, which plagues many studies, 

 by including information on fishing 

 effort. 



137 



