California Department of Fish and Game, Marine Resources Region
Abstract
The central California Dungeness crab resource had another season (1977-78) of low harvestable yield, 619,582 lb; while that off northern California yielded a higher than average seasonal harvest in excess of 13 million lb.
Crab egg hatching peaked in late December 1977. A tongue of freshwater
run-off from San Francisco Bay aided the offshore movement of zoeae.
No stage IV or V zoeae were taken in plankton tows, and only three megalopae were collected in the Gulf of the Farallones. The heavy winter rainfall reduced salinities of the Bay-estuarine complex, and no juvenile crabs were taken east of the Carquinez Bridge. By May most of the 1977
year class crabs had migrated into the Gulf. The first post-larval crabs of the 1978 year class appeared in May, 1 month later than in 1977. Both trawl and fish stomach samples revealed the 1978 year class to be weak as was that of 1976.
A comparison of ocean temperatures with crab landings, considered with evidence of laboratory experiments with crabs in various water temperatures, suggests that the extensive period (1957-72) of warmer water could be an explanation for the crab decline. Crabs held in the laboratory spawned, molted and spawned again, producing
fertilized eggs without having mated after molting.
Bioassays of crabs exposed to cadmium and silver show that the concentration lethal to 50% of the crabs within 96 hr was 6.8 mg/l for cadmium and 0.19 mg/l for silver. Levels of cadmium in hepatopancreas tissue of crabs used in acute bioassay reveal in excess of 20 times the concentration
of cadmium in the seawater within 24 hr.
Larvae cultured in the laboratory at ambient seawater temperature, (9 to 14 C) took approximately 60 days to develop from first stage zoeae to the megalopal stage, while larvae at 17 C took 31 days. (28pp. Harold G Orcutt(ed)
