Date Awarded

1973

Document Type

Thesis

Degree Name

Master of Science (M.Sc.)

Department

Virginia Institute of Marine Science

Advisor

Paul A. Haefner

Committee Member

Willard A. Van Engel

Committee Member

Joseph G. Loesch

Committee Member

George Grant

Committee Member

Robert J. Byrne

Abstract

The commercial seabass notting fishery and the trawl fishery in the Blackfish Bank area east of the entrance to Chincoteague Bay were used to study the biology of the rock crab, Cancer irroratus Say. Highest relative abundance of rock crabs occured in February, March, and April when coldest inshore (<30m) bottom water temperatures occurred. Relative abundance during all other months was extremely low. The apparent seasonal change in relative abundance may be due to an inshore-offshore seasonal migration of mature crabs following the seasonal inshore-offshore shift of colder bottom water. Male rock crabs grow to a significantly larger size than females. The carapace width range of males captured in the potting fishery was 66 to 141 mm; and 25 to 106 mm for females. In the trawl fishery the width range for males was 20 to 137 mm; and 22 to 102 mm for females. In both pot and trawl catches the male to female ratio was biased in favor of males. Males comprised 92% of the pot catch and 84% of all crabs captured by trawl. From August through December all crabs were in the hard shell intermolt stage. Small percentages of soft crabs occurred from January through June. Papershell crabs predominated in February, March and April. It is probable that most crabs molted in January and the process of exoskeleton hardening took several months. Ovigerous females were captured in seabass pots in April and June and in trawls from February through April. All ovigerous crabs were in hard shell condition. Gondal inspection of males and the presence of eggs on females indicated that rock crabs mature at a relatively small size (30 mm carapace width). Female rock crabs have a deeper body and wider abdomen than equivalent width males. Abdomen width grows more rapidly for females after the onset of sexual maturity than before. Mature females have a longer carapace than equivalent width males. Male and female regressions of chela length on carapace width could not be compared statistically but plots of the equations suggest no sexual difference. This dissertation is from the Joint Program Degree from the College of William & Mary and University of Virginia and awarded by the University of Virginia.

DOI

https://doi.org/10.25773/nnsq-nm50

Rights

© The Author

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