Estimated Preseason Abundance in the California Dungeness Crab (Cancer magister) Fisheries

Abstract

Annual preseason abundance for the central and northern California Dungeness crab (Cancer magister) fisheries is estimated from the decline in catch per unit of effort (CPUE) within each fishing season. The results support the common assumption that a large fraction of the available, legal size, male crabs are harvested each year; however, we noted regular changes in this fraction and also that it is rarely as high as previously assumed. In central California, annual exploitation rate was 92% during 1951–56 and declined to 72% following the collapse of the fishery. In northern California the annual exploitation rate varies with the 10-yr cycle of catch: 69% during the last few high catch years of each cycle, 84% in the first low catch year, and 54% during remaining low catch years and the first high catch year. The second high catch years are exceptions to a high exploitation rate. CPUE was saturated (i.e. did not decline) throughout the 1957 and 1977 fishing seasons. The large size of male crabs in the third and fourth high catch years also indicates high escapement in the second high catch years. Individual year-classes apparently may dominate the fishery for several years. This indicates that the time series of population abundance and recruitment is not as smoothly cyclic as the catch record.Key words: dungeness crab, Cancer magister, abundance, recruitment, catch per unit of effort