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



481 



4.5i 

 4.0 



§351 

 o:30i 



LU 



"■2.5 



0.5 1 



ROCK CRAB 



ALL AREAS 



r800 



^B SPRING 



□ FALL 



SPRING STA. 



— •— FALL STA 



,;., 



10 12 14 16 18 20 22 24 

 TEMPERATURE (C) 



JONAH CRAB 



ALL AREAS 



800 



600 



O 



h- 

 CO 



-400 



n 



LU 



200 3 



10 12 14 16 18 20 22 24 

 TEMPERATURE (C) 



NORTHERN LADY CRAB 



GEORGES BANK AND MIDDLE-ATLANTIC 



10 12 14 16 18 20 22 24 

 TEMPERATURE (C) 



O O 



COARSEHAND LADY CRAB 



MIDDLE-ATLANTIC AREA 



2 4 6 8 10 12 14 16 18 20 22 24 

 TEMPERATURE (C) 



Figure 6 



Mean abundance (unweighted) at bottom-water temperatures from spring and fall trawl surveys, with number of stations (lines) 

 at each temperature. 



highest partial correlation with abundance. On Georges 

 Bank, the most important variable was temperature 

 in summer and fall. In both subareas, temperature was 

 positively correlated with rock crab abundance. Sex 

 ratio was significantly associated with depth ♦tem- 

 perature (R, -0.355) and depth (R, +0.245) in fall; 

 however, no variables were significant in spring or 

 summer. 



Jonah crabs Jonah crabs were distributed on the 

 shelf and its upper slope from Penobscot Bay, Maine, 

 and Cape Sable, Nova Scotia, southward to Cape Hat- 

 teras, but were sparse south of Delaware (Fig. lla-d). 

 Jonah crabs were less abundant than rock crabs on 

 Georges Bank and in the middle- Atlantic. They oc- 



curred in all surveyed depths, but were least abundant 

 in 6-16 m (Fig. 5). The sediment where most Jonah 

 crabs occur is silty sand (Uchupi 1963, Schlee 1973). 

 They have also been collected on gravel and rocky 

 sediments (Jeffries 1966, Krouse 1980). 



A comparison of distributions in Figure 11 suggests 

 that Jonah crabs migrate toward the offshore edges 

 of the shelf in Georges Bank and the middle-Atlantic 

 subarea in winter and into their central portions in sum- 

 mer. Observations in the coastal zone of Maine (Krouse 

 1980) and in Narragansett Bay (Jeffries 1966), where 

 Jonah crabs were present in summer but not in winter, 

 confirm that seasonal migrations probably occur. How- 

 ever, data on offshore and inshore catch-per-tow (Table 

 2) and depth range (Fig. 5) show that migrations may 



