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Fishery Bulletin 89(3). 1991 



those reported earlier for the Gulf of Maine (Krouse 

 1980) and middle-Atlantic (Haefner 1977). 



Trawl catches of Jonah crabs were highest at night 

 in spring, summer, and fall, suggesting diel activity 

 cycles similar to those of rock crabs (Table 3). Under 

 artificial photoperiods, Jonah crabs are active only in 

 the dark period, with peak activity at dusk (Fogarty 

 1976). Our data also show differences in sex ratio by 

 time of day, especially in spring (Fig. 10), suggesting 

 differences in diel activity between the sexes. 



Male Jonah crabs were significantly more abundant 

 than females in spring trawl surveys, whereas females 

 were significantly more abundant in fall (Table 4). 

 These results are very similar to the findings of 

 Haefner (1977) for Jonah crabs off Virginia. Males 

 dominated the dredge catch in winter, though sample 

 size was small; females dominated the dredge catch in 

 summer. Seasonal changes in sex ratio may be due to 

 limited single-sex migrations or differences in catch- 

 ability reflective of the reproductive cycle. 



In the Gulf of Maine, from a limited number of indi- 

 viduals in this study, the sex ratio in spring trawl col- 



lections was 4.5:1 males and in fall 1.2:1 females. 

 Krouse (1980) found that in coastal Maine, males 

 dominated the catch in lobster pots in July and females 

 in August and September. He concluded that female 

 Jonah crabs occupy shallow zones during the latter two 

 months to molt and copulate. 



Differences in sex ratios of Jonah crabs offshore 

 and inshore in the middle-Atlantic were unlike those 

 of rock crabs (Fig. 9). Considering spring and fall, 

 when sample size was largest, the ratio of females to 

 males was higher inshore than offshore. In contrast, 

 in depths greater than 200 m, males outnumbered 

 females in both seasons. In contrast, in Haefner's 

 (1977) fall survey, sex ratios favored males from 

 41-60m depths and females from 61m to the survey 

 limit of 260 m. 



Most of the partial correlation coefficients of the en- 

 vironmental variables versus the catches in numbers 

 were lower for Jonah crabs than for rock crabs (Table 

 5). Perhaps this was because Jonah crabs were distrib- 

 uted rather evenly across all temperatures and depths 

 (Figs. 5, 6). In the middle-Atlantic, their abundance was 



