482 



Fishery Bulletin 89(3). 1991 



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ROCK CRAB 



ALL AREAS, FALL 



M NUMBER 

 (ZH WEIGHT 





I 



100 C5 



1978 1979 1900 1981 1982 1983 1984 1986 1986 1987 



JONAH CRAB 



ALL AREAS, FALL 



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1 



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1978 1979 I960 1981 1982 1983 1984 1985 1986 1987 



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NORTHERN LADY CRAB 



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COARSEHAND LADY CRAB 



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1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 



Figure 7 



Weighted mean catch-per-tow by number and weight (g), by year. Data are from fall trawl surveys. 



be minor, and much less extensive than in the rock 

 crab. 



Jonah crabs were collected at temperatures of 

 3-23°C (Fig. 6). Similarly, Haefner (1977) collected 

 Jonah crabs in the middle-Atlantic over a temperature 

 range of 6-24°C at depths of 150-400m, while max- 

 imum abundance of the species was from 8-14°C. 

 Krouse (1980) concluded that Jonah crabs have a 

 narrower temperature tolerance than rock crabs. We 

 found no difference in the annual temperature ranges 

 of the two species. However, in spring, the majority 

 of rock crabs occurred at 3-7 °C when they were con- 

 centrated inshore, while the majority of Jonah crabs 

 occurred at 8-12° C because they were mostly offshore. 



The scarcity of Jonah crabs off the coasts of Mary- 

 land, Virginia, and North Carolina (Fig. 11) may be due 



to unfavorably high temperatures. Average bottom 

 temperatures in that area in August and September 

 are 18-23°C. At those latitudes, Jonah crabs were 

 more abundant on the outer shelf and slope, where 

 temperatures are mostly 14-18°C during those months 

 (Mountain and Holzwarth 1989). 



Mean catch-per-tow by number and weight varied 

 among years (Fig. 7). It was roughly similar during 

 1978-84 and in 1987. However, it was nearly twice as 

 high in the years 1985 and 1986. 



Carapace widths of Jonah crabs differed by sex. In 

 all three subareas, males had a broad range of widths, 

 while females had sharp modal peaks of 10, 12, and 

 8 cm, in the Gulf of Maine, Georges Bank, and middle- 

 Atlantic, respectively (Fig. 8). Few females attained 

 widths of >13cm. These size ranges correspond to 



