Impact of fishing on life histories

Artificial selection pressures imposed by fisheries can impact population structure in the short term and drive evolution of life-history traits in the long term. In exploited squid populations the short life span and lack of mating between generations is likely to intensify the effects of artificial selection. Selection on size, age and maturity status can occur through the physical characteristics of the gear or by non-random fishing effects. In squids of the genus Illex there is considerable variation in overall growth rate, the size at which sexual maturation commences, the rate at which maturation proceeds and the size at which full maturation is reached. Although there are no data on heritability of fitness traits in squid it is unlikely that additive genetic variance in growth rate would be less than in fish, where life-history parameters have been shown to be susceptible to selective breeding. Model studies indicate that there is a large potential for selective effects to occur in exploited squid populations. The fishery can greatly influence the population structure and reproductive potential of a particular cohort. Analyses of life-history functions can be used to investigate how changes in mortality rate can affect the age of maturation. The temporally restricted effects of exploitation within a season may have important consequences for the evolutionary responses of a species. Suitable long-term data sets for squid fisheries should be examined for evidence of the selective effects of fishing on life-history traits