8-27 



In a study of the rock crab, Cancer irroratus , and the spider 

 crab, Libinia emarginata, in Delaware Bay, Winget et al . (1974) observed 

 that the occurrence of C. irroratus was generally opposite that of 

 L. emarginata. Whereas Cancer was most abundant from November through 

 April, Libinia was generally most abundant from April through late 

 October. and early November. In New Haven Harbor Libinia has been col- 

 lected in relatively low numbers; however, as demonstrated by Winget et 

 al . , it has occurred most abundantly from June through October when 

 Cancer abundance in the harbor was low. No apparent interrelationship 

 of the species exists that would account for the relationship between 

 the migratory patterns of these two species; however, it is reasonable 

 to assume that competition for available food and habitat resources is 

 diminished by this general migratory scheme. Differences in the migra- 

 tory pattern of these two species could also be related to differences 

 in their temperature tolerances. Cancer is a boreal species, and as 

 such is more tolerant of cold temperatures and less tolerant of high 

 summer temperatures. Libinia on the other hand, is more of a warm- 

 water species, and therefore, is more tolerant of high summer temp- 

 eratures and less tolerant of low winter temperatures. 



Although it is not certain when Cancer spawns in New Haven 

 Harbor, evidence indicates that spawning (egg extrusion and fertiliza- 

 tion) takes place during late fall or winter, brooding continues into 

 spring and the developing eggs hatch into planktonic larvae in late 

 spring-early summer (NAI, 1978a, 1977 and 1976a) . Scarrett and Lowe 

 (1972) reported peak abundances of Cancer larvae in the Northumberland 

 Strait, Gulf of St. Lawrence, during late summer. Krouse (1972) indicated 

 that C. irroratus spawn during late fall-early winter along the Maine 

 coast and that eggs hatch during the spring. During 1977 the abundance 

 of Cancer larvae in New Haven Harbor was relatively low, but peak abun- 

 dances occurred during June (NAI, 1978a). Prior to 1977, Cancer larvae 

 were not specifically identified, but decapod larvae, which probably 

 included Cancer, were present in the plankton only from May through 

 August. Since Cancer begins its migration to deeper waters during April 

 and May, it can be expected that a substantial amount of larval develop- 

 ment occurs outside the harbor. This is important in two respects. The 



