Dungeness crab research program: report for the year 1978

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)

Dungeness crab research program

In 1974, the California State Legislature, recognizing the problem of low yields from the Dungeness crab resource of central California, directed the Department of Fish and Game to conduct an investigation into the causes of the decline. The Operations Research Branch of the Department has conducted preliminary studies and field operations necessary to formulate the Dungeness Crab Research Program. The objectives, research design, and work plans are presented for a 4-year program from July 1, 1975 through August 31, 1979. (38pp.

Dungeness crab research program: Report for the Year 1976

All larval stages of the 1976 year class, with the exception of the 5th zoeal stage, were found in Gu1f waters January through March. The first post-larval stage was collected in San Pablo Bay in May. Fifty percent of 1976 year class crabs entered the Bay complex as compared to nearly 80% in 1975. The 1976 year class appears relatively weak. No electrophoretic polymorphism was found in Cancer magister to be of value in Dungeness crab population determinations. Multi-variate correlations comparing crab landings with an array of oceanographic parameters and the crab density dependent factor were computer-run for both northern and central California. The most significant correlating factors at the time late stage larvae prevail were sea level and atmospheric pressure for central California and, for northern California, the density dependent factor and sea surface temperature. Female crabs held at controlled temperatures indicated gonad maturation and spawning may be induced by increased temperature. Analyses of crab tissues revealed burdens of petroleum hydrocarbons, silver, selenium, cadmium, and PCB's higher in central California crabs, while DDE was found in higher amounts in northern California crab tissue. Thru-flow culture systems were developed which should yield about 163 megalopae of Dungeness crabs in 63 days from 1,200 laboratory hatched zoeae.(46pp.