Aspects of Molting, Growth and Survival of Male Rock Crabs, Cancer irroratus, in Chesapeake Bay

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Abstract
Male rock crabs,Cancer irroratus, were collected from the lower Chesapeake Bay during the winter dredge seasons of 1970–1973. Crabs migrate into Chesapeake Bay in late fall, molt extensively in January, remain in papershell condition until late March and April and leave the bay in May. Most crabs held in the laboratory molted in January, only 18% in February, thus confirming the pattern observed in the field. The molting season of male rock crabs appears to be related to decreasing seawater temperature. Signs of an approaching molt were determined by examining the mouth parts microscopically, and by testing the resiliency of the shell in the vicinity of the ecdysial suture line. Crabs larger than 100 mm carapace width did not molt. Progression of crabs through the intermolt cycle was dependent on temperature: crabs held at 17.5 C advanced from hardshell (C4) to papershell (B2) in one-third the time required for crabs held at 7 C. Most water uptake and weight change occurred between advanced peeler (D4) and soft crab (A2) stages; mean percent water content ranged from 67% for C4 to 87% for A2 stages. Mean percent increase in weight ranged from 52 to 59% in relation to size. Progressive growth occurred in length, width and weight; percent increment ranged from 18 to 23 for length, 19 to 27 for width and 52 to 82 for weight. Width-weight relationships of premolt and postmolt crabs were significantly different. Temperature-salinity tolerance experiments revealed that more crabs survived in 7 C than in 17.5 C. Stage B1–B2 crabs exhibited the highest survival and C1−C3 crabs the least. Maximum survival occurred within the salinity range 14–21‰. Papershell crabs were isosmotic to polyhaline salinities but were hyperosmotic at lower salinities. Those acclimated at 7 C approached isosmoticity near 28–30‰. Warm acclimated crabs were isosmotic near 24–26‰ but showed limited hyperregulation at salinities less than 20‰.

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