EFFECT OF INDIVIDUAL GROWTH-RATES ON EXPECTED BEHAVIOR OF THE NORTHERN CALIFORNIA DUNGENESS CRAB (CANCER MAGISTER) FISHERY

Cycles in the northern California dungeness crab (C. magister) fishery may be caused by density-dependent recruitment or a cyclic environmental variable. Investigation of these potential causes requires knowledge of the age(s) at which crabs enter the fishery. Behavior of this fishery was previously analyzed using mathematical models that include density-dependent recruitment and describe changes in age structure with time. Data available on the northern California crab population and a review of previous studies elsewhere indicate that a single year-class of crabs enters this fishery over several years rather than in 1 yr as described by models with only age structure. The realism of models of this fishery can thus be increased by including size structure. Behavior of size-specific models is in general different from that of age-specific models. An effective survival rate can be derived from a size-specific model that enables interpretation as an age-specific model. This is used to demonstrate that inclusion of size dispersion in a population model increases stablity, but if the mean age of the population is not changed, it will not substantially change the period of cycles. Because the growth pattern developed here changes the mean age of entry into fishery it results in cycles with a longer period than determined in previous analyses. With regard to environmental causes, this growth pattern implies time lags of 4 and 5 yr between an environmental factor affecting the recruitment and its effect on the catch record.