Stehlik et al.: Distribution and abundance of brachyuran crabs on northwest Atlantic shelf 



479 



ROCK CRAB 



ALL AREAS, TRAWL 



46.7 16.0 



g 30 



O 



UJ 



°- 2.0 



I 



o 



S 16 



< 



UJ 



0.5 

 0.0 



^1 SPRING 

 Bffl SUMMER 

 CD FALL 



55 



M 



M\M I ^~m 



H < I 



-16 17-26 27-40 41-60 61-80 61-100 101-200 

 DEPTH RANGE (M) 



JONAH CRAB 



ALL AREAS, TRAWL 



6-16 17-26 27-40 41-60 61-80 81-100 101-200 >200 



DEPTH RANGE (M) 



NORTHERN LADY CRAB 



GEORGES BANK AND MIDDLE-ATLANTIC, TRAWL 



5.5- 



5.0- 

 4 5- 

 4.0 

 3.5 



30- 

 2.5 

 2.0 

 1.6- 



1.0 

 0.5 

 0.0 



_JL 



17-26 27-40 41-60 61-80 81-100 101-200 

 DEPTH RANGE (M) 



COARSEHAND LADY CRAB 



MIDDLE-ATLANTIC AREA, TRAWL 



O 



o_ 



X 0.20 

 O 



z 



< 0.10- 

 LU 



0.05 

 0.00 







_□_ 



XL 



6-16 17-26 27-40 41-60 61-80 81-100 101-200 >200 



DEPTH RANGE (M) 



Figure 5 



Mean catch-per-tow (unweighted) at depth ranges for rock, Jonah, northern lady, and coarsehand lady crabs in spring, sum- 

 mer, and fall trawl surveys. The first two depth ranges, 6-16 and 17-26m, are within inshore strata of the trawl surveys. 



In the middle- Atlantic, male rock crabs were distrib- 

 uted closer to shore than females. A larger proportion 

 of males occurred inshore than offshore in spring and 

 summer trawl surveys, and a larger proportion of 

 females occurred offshore than inshore in dredge 

 surveys (Fig. 9). Males are also dominant in estuaries 

 such as lower Delaware Bay (Winget et al. 1974) and 

 lower Chesapeake Bay (Terretta 1973), where they 

 overwinter (Haefner and Van Engel 1975), and along 

 the Virginia coast (Shotton 1973). 



While different migratory patterns of the sexes 

 might partially account for the unequal sex ratios in 

 rock crab catches in this study, we consider differences 

 by sex in availability to sampling gear to be largely 

 responsible. Comparing catches of rock crabs in winter 



dredge surveys with spring trawl surveys, both of 

 which were conducted during the cold season, signifi- 

 cantly more females were caught than males by 

 dredges, whereas significantly more males than 

 females were caught by trawls (Table 4). This suggests 

 that females bury more than males. The two summer 

 surveys showed the same phenomenon. Our spring 

 trawl data showed the ratio of males to females was 

 lowest at night (Fig. 10), from which we conclude that 

 diel activity rhythms at that season may be different 

 by sex, and that females are more active at night than 

 by day. They would be buried when inactive during 

 daylight hours. 



Inactivity of females may be related to the reproduc- 

 tive cycle. Females extrude eggs in fall, which are 



