Casco Bay, the Sheepscot and Damariscotta estuaries, upper Penobscot Bay, and 

 Blue Hill Bay. 



Life History 



The sexes of rock and Jonah crabs are separate, and in Maine breeding occurs 

 in the fall when females are molting (males molt later, in February or March). 

 Copulation occurs just after the female molts and the several thousand eggs 

 are extruded in late fall or early winter. Fertilized eggs are carried by the 

 female from 6 to 9 months until they hatch. Krouse (1976) estimates that 

 hatching occurs from June to August in the Gulf of Maine and that the larvae 

 are planktonic until August or September (approximately 40 to 60 days). 



Krouse (1976) found that young crabs settle in the intertidal zone and remain 

 there until the second year of life, or until they reach a size of 1.9 inches 

 (50 mm). Then, when the temperature begins to drop, they migrate seaward. 

 Growth slows considerably in winter. 



Both species are carnivores and feed on polychaetes, sea urchins, mussels, and 

 starfish (Scarratt and Lowe 1972). 



Habitat Preferences 



For the first 1.5 to 2 months of life, crabs are pelagic and part of the 

 meroplankton (floating eggs and larvae). As such they are subject to heavy 

 predation. 



The two species inhabit different bottom types. The Jonah crab is found 

 predominantly in rocky bottoms, where shelter is readily available. The young 

 rock crab, under 1.9 inches (50 mm), settles on rocky bottom or rocky 

 intertidal areas but may later shift to a more open environment, such as 

 unconsolidated bottoms of sand or mud (Stasko 1975; and Scarratt and Lowe 

 1972). The rock crab is more active than the Jonah crab and burrows quickly 

 in unconsolidated bottoms, or runs, when approached by predators (Jeffries 

 1966). The Jonah crab, when approached by predators, finds a crevice on a 

 rocky bottom and defends itself with its large claws. 



Factors of Abundance 



The rock and Jonah crabs have a limited tolerance to extreme environmental 

 fluctuations . Larval mortality is high in salinities under 20 ppt (Sastry 

 1970). Jeffries (1966) found, using "walking ability" as an indicator of 

 temperature effects on adults of both species, that optimal temperature for 

 the rock crab was 57 to 64°F (14 to 18° C) and for the Jonah crab, 43 to 57° F 

 (6 to 14 C). 



Predators on small crabs include various bottom-feeding fish and the American 

 lobster. Mature crabs are sometimes preyed upon by large cod (TRIGOM 1974). 



12-19 



10-80 



