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Fishery Bulletin 89(1), 1991 



reported that juvenile males and females of the 1980 

 year-class in Grays Harbor, Washington, disappeared 

 during the winter of their first year, then reappeared 

 the following spring. Gotshall (1978) observed move- 

 ment of sublegal- and legal-sized male crabs in northern 

 California to deeper water in winter, and a return to 

 shallower water in spring. It is reasonable to surmise 

 that the autumn movement to deeper water is to avoid 

 rough shallow water during the winter. Returning to 

 shallower, warmer, and more productive water during 

 summer could enhance growth and survivorship. 



Our estimated average daily displacement rate for 

 male Dungeness crabs of =300m/day, is consistent with 

 our inferences on movement from our mark-recovery, 

 beam-trawl, and trap sampling results. Our general 

 conclusion of limited movement is also consistent with 

 the results of other tagging studies. Both Butler (1957) 

 for Dixon Entrance, British Columbia, and Gotshall 

 (1978) for northern California, suggested that Dunge- 

 ness crab populations remain local. With the exception 

 of the apparent seasonal shift in habitat, no studies 

 suggest migratory movements for males; however, 

 Gotshall (1978) noted that males seem to move in the 

 direction of prevailing currents off northern Califor- 

 nia. Bennett and Brown (1983) report that most tagged 

 males of the closely related crab Cancer pagurus re- 

 mained near where they were released in the English 

 Channel. 



Our acoustic tagging and mark-recovery data sug- 

 gest that female Dungeness crab undergo only limited 

 movement. Diamond and Hankin (1985) similarly ar- 

 gued that mature female Dungeness crab off the coast 

 of northern California undergo limited movements and 

 suggested that females constitute localized stocks. Dia- 

 mond and Hankin (1985) do suspect that females move 

 short distances to shallower water in spring to mate 

 and molt. Our analyses provided no evidence of this, 

 but it is quite conceivable that both males and females 

 could improve mating opportunities by concentrating 

 in shallow water (Butler 1960). 



We inferred, mainly from our beam trawl and trap 

 samples, that females tended to move from coastal in- 

 lets to an area more exposed to the open coast (zone 

 6, Fig. 1). In the inlets the substrate ranged from mud 

 to a mud/sand mix, whereas in the more exposed area 

 the bottom was mainly sand or a sand/gravel mix. Wild 

 (1980) states that females must be at least partially 

 buried in sandy substrate to extrude and incubate eggs 

 so our inference is consistent with the current under- 

 standing of the life history of Dungeness crab females. 

 Stevens and Armstrong (1984) noted that egg-bearing 

 females were rare in Grays Harbor, and speculated that 

 most mature females left the harbor to incubate and 

 release their eggs in a preferred environment. Our 

 study yielded an average daily displacement rate for 



females (=400m/day) which was significantly (P<0.01) 

 more than the rate for males (=300 m/day), and which 

 might be explained by females undergoing deliberate 

 migratory movements to locate suitable substrate for 

 incubating eggs. 



Similar movement behavior has been reported for 

 females of other crab species. Hyland et al. (1984) ob- 

 served the movement of female portunid crab Scylla 

 serrata from an estuarine environment, where they 

 lived as juveniles, to the open ocean where they re- 

 leased their eggs. Some females returned to inshore 

 waters after the hatching season. Bennett and Brown 

 (1983) demonstrated that female C. pagurus undergo 

 extensive movements, apparently to locate habitat 

 more suitable for egg incubation and release. While 

 SCUBA diving, Howard (1982) observed egg-bearing 

 female C. pagurus congregated in relatively deep 

 (24 m), quiet water. Since they were rare elsewhere, 

 he concluded this was a preferred habitat. Dinnel et 

 al. (1987) observed a similar behavior for Dungeness 

 crab in Puget Sound, Washington, from the Govern- 

 ment of Canada submersible Pisces IV. 



Our simultaneous analysis of Dungeness crab move- 

 ment and mortality using mark-recovery and fishing- 

 effort data diminished the confounding of these two 

 processes and yielded a revised estimate of the natural 

 mortality rate originally proposed by Smith and Jamie- 

 son (1989b). Our (mainly) natural mortality rate esti- 

 mate for males of 2.5 (95% CI of 2.3-2.8) is moderate- 

 ly lower than our previous estimate of 2.9-4.5, probably 

 because of dispersal of tagged crabs into zones (espe- 

 cially zone 6) with low fishing intensities. 



Our estimate of female natural mortality of 1.3 (95% 

 CI of 0.8-1.8) is significantly lower than that of males 

 but in general agreement with the mortality estimates 

 of Hankin et al. (1985, 1989) for females in northern 

 California. They estimated annual instantaneous nat- 

 ural mortality for females greater than 140 mm CW at 

 2.0 and 2.5 for two different periods of release in a 

 mark-recovery experiment. For females 125-140mm 

 CW their rough estimate was =0.7, a more precise 

 estimate being unobtainable due to females this size 

 having a high probability of molting and changing 

 vulnerability to traps. Our estimate of 1.3 is based on 

 a group of tagged females whose carapace widths at 

 release were 135-171 mm (x 150mm), thus our esti- 

 mate seems consistent with those of Hankin et al. 

 (1985, 1989). 



The estimates of male and female natural mortality 

 from this study, and of female natural mortality from 

 Hankin et al. (1985, 1989), for crabs near the Canadian 

 minimum legal size limit of 154 mm CW (165 mm spine- 

 to-spine CW) increases our confidence that mortality 

 of mature Dungeness crab is indeed high. For exam- 

 ple, a mortality rate of 2.0 means only 13.5% annual 



