DISTRIBUTION AND ABUNDANCE OF 4 BRACHYURAN CRABS ON THE NORTHWEST ATLANTIC SHELF

Seasonal distributions and relative abundances of the Atlantic rock crab Cancer irroratus, Jonah crab C. borealis, northern lady crab Ovalipes ocellatus, and coarsehand lady crab O. stephensoni were determined from fish trawl and clam dredge surveys on the continental shelf from Nova Scotia to Cape Hatteras, North Carolina during 1978-87. Rock crabs have the broadest distribution, 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 frequently in the northern and offshore zones of the middle Atlantic from south of Georges Bank to off Delaware, at depths to over 400 m. Northern lady crabs occur primarily in the inner strata of the middle-Atlantic shelf in depths < 27 m, 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-degrees-C, while Ovalipes spp. occur mainly at 11-24-degrees-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 significantly larger at night or twilight than during the day, suggesting more nocturnal activity. Temperature, depth, and their interaction significantly affected the catches of these crabs.