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 su ccess on effective population size (N-e) in populations with type III survi vorship curves. Special emphasis is put on determining the causes for the l arge differences in the genetic variability between populations of Pacific sardine (Sardinops sagax) and northern anchovy (Engraulis mordax). The resu lts 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 populati on, but the sensitivity of this ratio to environmental fluctuations is inve rsely proportional to the generation overlap. The larger the generation ove rlap, the smaller the impact of environmental fluctuations on the level of genetic variability maintained by a population. The large difference in het erozygosity between Pacific sardine and northern anchovy populations is lik ely due to both life history differences between the two species and a rece nt arrival (founder event) of the Pacific sardine population to the Califor nia Current System.