A summary of the dungeness crab research program 1974-1980
In 1974, the State Legislature directed the Department of Fish and Game to investigate causes of a long-term decline in Dungeness crab, Cancer magister, commercial fishery landings in central California. The Departmentestablished the Dungeness Crab Research Program which conducted investigations on crab life history, pollution, and oceanography.Genetic studies to determine if there were different stocks along the coast were inconclusive. Early larval stages (zoeae) drifted progressively offshore as they developed. The last stage larvae (megalopae) were foundin nearshore waters. San Francisco Bay was determined to be an important nursery ground for juvenile crabs which contribute substantially to the local coastal adult stock. Many species of fish were found to prey upon larval and juvenile crabs. Silver salmon preyed heavily upon megalopae.Chlorine-treated sewage wastes slowed responses of juvenile crabs but present waste treatment practices (dechlorination before discharge) apparently are not harmful. No harmful effects of other pollutants (traceelements, pesticides, PCB's, and oil) were detected at levels which were found in crab tissues and the Bay environment.A long-term oceanographic change, characterized by increased ocean temperatures and stronger northward-flowing winter currents was found to coincide with the crab decline. These conditions appear to have biologicaleffects on crabs. San Francisco crabs were found, on the average, to have smaller ovaries than Eureka crabs. In the laboratory, crab egg mortality was greater in increased seawater temperatures.Overall conclusions are that the primary factors responsible for the crab decline are long-term changes in ocean conditions which have affected egg production and survival, and distribution of larvae.(16pp.)
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| Format: | monograph biblioteca |
| Language: | English |
| Published: |
California Department of Fish and Game, Marine Resources Region
1981
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| Subjects: | Fisheries, Biology, Dungeness crab, Cancer magister, commercial fishery, |
| Online Access: | http://hdl.handle.net/1834/18140 |
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