AbStr3Ct. — Seasonal distributions 

 and relative abundances of the At- 

 lantic rock crab Cancer irroratus, 

 Jonah crab C. borealis, northern lady 

 crab Ovalipes ocellatus, and coarse- 

 hand lady crab 0. stephensoni were 

 determined from fish trawl and clam 

 dredge surveys on the continental 

 shelf from Nova Scotia to Cape Hat- 

 teras, North Carolina during 1978-87. 

 Rock crabs have the broadest distri- 

 bution, which includes coastal waters 

 of the Gulf of Maine and depths 

 of 6-456 m from Georges Bank to 

 Cape Hatteras. Jonah crabs are 

 more widely distributed in the Gulf 

 of Maine and on Georges Bank than 

 rock crabs. They occur most fre- 

 quently in the northern and offshore 

 zones of the middle Atlantic from 

 south of Georges Bank to off Dela- 

 ware, at depths to over 400 m. 

 Northern lady crabs occur primarily 

 in the inner strata of the middle- 

 Atlantic shelf in depths <27m, and 

 on shallower portions of Georges 

 Bank. Coarsehand lady crabs occur 

 from southern New Jersey to Cape 

 Hatteras, to over 200 m. Cancer spp. 

 occur mainly at 3-18 c C, while Ova- 

 lipes spp. occur mainly at 11-24°C. 

 Sex ratios in rock and Jonah crab 

 catches deviated from 1:1 by season 

 and gear; males dominate in spring 

 trawl surveys, females in summer 

 dredge and fall trawl surveys. Trawl 

 catches of all species were signifi- 

 cantly larger at night or twilight 

 than during the day, suggesting 

 more nocturnal activity. Tempera- 

 ture, depth, and their interaction 

 significantly affected the catches of 

 these crabs. 



Distribution and Abundance of 

 Four Brachyuran Crabs on the 

 Northwest Atlantic Shelf 



Linda L. Stehlik 

 Clyde L. MacKenzie Jr. 

 Wallace W. Morse 



Sandy Hook Laboratory, Northeast Fisheries Science Center 



National Marine Fisheries Service, NOAA, Highlands, New Jersey 07732 



Manuscript accepted 12 April 1991. 

 Fishery Bulletin, U.S. 89:473-492 (1991). 



The most common species of brachy- 

 uran crabs on the northwest Atlan- 

 tic continental shelf are the Atlantic 

 rock crab Cancer irroratus (subse- 

 quently referred to as rock crab), 

 Jonah crab C. borealis, northern lady 

 crab Ovalipes ocellatus, and coarse- 

 hand lady crab O. stephensoni. Knowl- 

 edge of their distributions is incom- 

 plete, largely because previous sur- 

 veys were geographically limited, 

 survey stations were sparse, or sur- 

 veys were conducted in one season 

 only (Musick and McEachran 1972; 

 Shotton 1973; Haefner 1976, 1977, 

 1985; Williams and Wigley 1977; 

 Bigford 1979; Williams 1984). No 

 documented information was avail- 

 able on interannual fluctuations in 

 abundance for any of the crabs. 



This study was undertaken to in- 

 vestigate shelf-wide seasonal distri- 

 butions and abundance fluctuations 

 of the four crab species over a ten- 

 year period. Our goals also included 

 providing information about sedi- 

 ments on which the crabs occur, 

 depth ranges, water temperature 

 preferences, size frequencies, sex 

 ratios, and diel catches. 



Methods 



Data were obtained from groundfish 

 trawl and clam dredge surveys con- 

 ducted by the Northeast Fisheries 

 Center (NEFSC), National Marine 

 Fisheries Service, over the continen- 

 tal shelf from the northern Gulf of 

 Maine to Cape Hatteras, for the ten- 



year period 1978 through 1987. The 

 data set consisted of 11,211 stations: 

 8776 trawls and 2435 dredges. Sta- 

 tion locations were selected using a 

 stratified-random design based pri- 

 marily on depth (Grosslein and 

 Azarovitz 1982, Murawski and Ser- 

 chuk 1989). Density of trawl stations 

 was 1/500 km 2 for inshore strata 

 (depth <27m) and 1/1000 km 2 for 

 offshore strata (depth 3* 27 m). Clam 

 dredge stations were spaced at 1/460 

 km 2 . 



The area covered by trawl surveys 

 in late February-May, designated as 

 spring, and September-November, 

 designated as fall, included the shelf 

 and its upper slope between Nova 

 Scotia and Cape Hatteras. Tow 

 depths in spring and fall were 6-456 

 m. Trawl surveys in January-Febru- 

 ary, designated as winter, and July- 

 August, designated as summer, were 

 limited to depths of 6-203 m. Spring 

 and fall trawl surveys were con- 

 ducted in each of the ten years, 

 winter trawl surveys in 1978 and 

 1981, and summer trawl surveys 

 from 1978 through 1981. Clam dredge 

 surveys were conducted during 

 winter in December, January, and 

 February (1978-80) and summer in 

 July and August (1978-86) from 

 Georges Bank to Cape Hatteras at 

 depths of 9-1 10m (Table 1). Bottom 

 water temperatures were taken at all 

 stations. 



In our analysis, the shelf was divided 

 into Gulf of Maine, Georges Bank, 

 and middle- Atlantic subareas (Fig. 1). 



473 



