FISHERY BULLETIN: VOL. 77, NO. 3 



lated European edible crab, C. pagurus, have also 

 been observed to undertake similar seasonal 

 movements off the coast of England (Brown^). Li- 

 mited population movements of Jonah crabs has 

 also been suggested by Haefner (1977). 



Althiiu^h .Jonah cralis weiX' caught at each sta- 

 tiiin, their relative abundance varied markedly liy 

 area as reflected by CPUE values which ranged 

 from 0.01 to 0.12 (Table 1 ). Jonah crabs were more 

 numerous at the generally deeper, more seaward 

 station.s i East Southport, Sc|uirrel Island, and 

 Damariscove Island) characterized by rocky sub- 

 strates and within the Sheepscot River at .Middle 

 Mark Island where the fishing area borders rela- 

 tively deep water (45 ml and the bottom is hard- 

 packed mud interspersed with rock outcroppings. 

 Conversely,. Jonah crabs were sparsely distributed 

 at the otherstations in the Sheepscot estuary ( Up- 

 per Mark Island. (Jreen Island, and Powderhorn 

 Island! which in contrast to Middle Mai k Island 

 are c|uite shallow with soft mud bottoms. Thus, the 

 data indicate that the distribution and abundance 

 of Jonah cralis reflects bottom type as well as 

 depth. 



Comparisons (jf CPUE for rock crabs with those 

 for Jonah crabs at different sampling sites re- 

 vealed an inverse relationship iTable Ii. Rock 

 crabs were very abundant at those stations within 

 the Sheepscot River (CPUE: 2.6-7.6) where Jonah 

 crabs were scarce; whereas, at other areas where 

 Jonah crabs were more plentiful rock crabs were 

 less common (CPUE: 0.7-2.1 1. Based on these ob- 

 servations, rock crabs seem to prefer inshore areas 

 with mud bottoms while Jonah crabs favor sea- 

 ward locations with rocky substrates. This agrees 

 with Jeffries ( 1966i findings that the same two 

 cancrid crabs are separated spatially in Nar- 

 ragansett Bay according to bottom type: rock and 

 Jonah crabs inhabit sand and rock substrates, re- 

 spectively. Interestingly, in the more northern 

 latitudes, juvenile rock crabs, unlike the adults, 

 show preference for coarse, rocky bottoms (Scar- 

 ratl and Lowe 1972; Krou.se 1972; Reilly and Saila 

 197H). where protection from predators would be 

 optimum. 



Distribution of both cancrid crabs is not only 

 related to substrate type and depth, but is also 

 dependent upon water temperature. For example, 

 in the mid-Atlantic region, Carpenter (1978) 

 found Jonah crabs at temperatures from 5° to 15° C 



■'Brown. C;. C;. IflT.'i. Nciilnlk ctmIi inve..itigatu>ns I969-7:i 

 I.al). I.i'afl .ill, 12 p Fi,-h I.ah . Lmvc.'^tcilt, .SiilTolk, Kngland 



with ma,\imum abundance between 6" and 12° C, 

 Similarly, Haefner ( 1977) reported Jonah crabs to 

 be most numerous in the temperature range of 

 8°-14° C. The more eury thermal rock crabs have 

 been observed to be widely distributed over the 

 continental shelf of the Mid-Atlantic Bight and 

 most abundant inshore particularly during winter 

 when temperatures are lowest (as low as 2° C) 

 iMusick and McEachran 1972; Haefner 1976). In 

 Chesapeake Bay rock crab abundance increases 

 markedly in winter (2°-8° C ) and declines in spring 

 as temperatures warm (Shotton 1973; Terretta 

 1973). In view of these data, the distribution of the 

 two cancrid crabs along the Maine coast may be 

 further e.xamined in relation to temperature. Rock 

 crabs have been found to be most abundant in 

 shallow nearshore waters where temperatures 

 may vary from near 0° C in winter to 18° C in 

 summer (Welch''); whereas, Jonah crabs are more 

 numerous at greater depths where temperatures 

 are more stable. Likewise, in the Gulf of St. Law- 

 rence where the temperature regime is great ( -2° 

 to 20° C [Lauzier and HuU'l), rock crabs are com- 

 mon and Jonah crabs are nonexistent (Squires 

 1966; Scarratt and Lowe 1972). 



Thus, it appears that the distribution of these 

 congeneric species in the northern part of their 

 range is dependent upon substrate, depth, and 

 temperature. 



Sex Ratios 



Initially, I examined ratios of male to female 

 Jonah crabs in monthly catches at each fishing 

 site; however, due to the small sample sizes for 

 several of the groups, area catches were combined 

 by month ( Table 2 ). The chi-square test, which was 

 usedonly when the monthly N was slO, indicated 

 that July through September ratios deviated sig- 

 nificantly (P = 0.05) from 1:1. Males dominated in 

 July while during August and September there 

 was a preponderance of females. This shift in sex 

 ratios may be attributed to an apparent movement 

 of female crabs into warmer shoal water during 

 summer and early fall as the result of behavior 

 associated with molting and copulating. The 

 closely related Dungeness crab, C. magister, and 



■•W. R. Welch, Marine Resources Scientist, Maine Department 

 of .Marine Re.sdurce.s, West Boothbay Harbor, MK MWl^. pers 

 commun. February 1979. 



"Lauzier, I,. M., and .J H. Hull 1969. Coastal .station data 

 temperatures along the Canadian Atlantic coast 1921- 

 19H9. Ki.sh Res. Board Can. Tech. Rep. l.iO. 2.5 p. 



690 



