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Fishery Bulletin 89(3). 1991 



carried until hatching in spring (Krouse 1972). Con- 

 versely, perhaps some of the more active males avoid 

 a slowly towed dredge but cannot avoid a trawl because 

 it is too large. Haefner's (1976) trawl surveys, which 

 showed significantly more males than females, must 

 have caught the active males and missed the buried 

 females. 



There are a few possibilities as to why rock crabs in 

 the middle- Atlantic migrate inshore in fall and remain 

 until spring. Perhaps they do so to feed when poten- 

 tial competitors for prey, such as the blue crab Calli- 

 nectes sapidus and northern lady crab, both of which 

 occur inshore, are dormant in winter. Rock crabs are 

 the only brachyurans in the subarea which molt in 

 winter (Haefner and Van Engel 1975), and it is pos- 

 sible that they migrate inshore to avoid fishes which 



could prey on them while they are in the vulnerable soft 

 and paper-shell stages. The latter stage in adults 

 persists for two to three months (Haefner and Van 

 Engel 1975). Another possibility is that their larval 

 stages survive better in coastal zones when released 

 in spring. 



The environmental variables that accounted for the 

 largest proportion of the variance of rock crab abun- 

 dance in the middle-Atlantic subarea were depth in 

 spring and temperature in summer and fall (Table 5). 

 The slope of the regression of depth upon abundance 

 was negative in that subarea in all seasons and was 

 strongest in spring (compare with Figure 5). Temper- 

 ature was also negatively correlated with rock crab 

 abundance in that subarea. In the Gulf of Maine, depth 

 and the cross-product, depth * temperature, had the 



