Effect of life history strategy, environmental variability, and overexploitation on the genetic diversity of pelagic fish populations

We study the effect of recruitment failures and variance in reproductive success on effective population size (N-e) in populations with type III survivorship curves. Special emphasis is put on determining the causes for the large differences in the genetic variability between populations of Pacific sardine (Sardinops sagax) and northern anchovy (Engraulis mordax). The results indicate that moderate differences in life history between ecologically related species can lead to substantial differences in N-e. The effect of fluctuations in vital rate parameters induced by environmental changes on N-e depends on the life history of each species. The ratio of N-e to census size is directly proportional to the total reproductive value of a population, but the sensitivity of this ratio to environmental fluctuations is inversely proportional to the generation overlap. The larger the generation overlap, the smaller the impact of environmental fluctuations on the level of genetic variability maintained by a population. The large difference in heterozygosity between Pacific sardine and northern anchovy populations is likely due to both life history differences between the two species and a recent arrival (founder event) of the Pacific sardine population to the California Current System.