Wide-spread genetic variability and the paradox of effective population size in the gag, Mycteroperca microlepis , along the West Florida Shelf

Wide-ranging marine species are often described as having a low effective population size (N e) to census size (N) ratio. This genetic phenomenon is typically attributed to large variation among individuals in reproductive success because of the high mortality rates and unpredictable environments associated with larval dispersal. In this study, we examined patterns of genetic variation in gag (Mycteroperca microlepis) on the West Florida Shelf across year classes of post-settlement juveniles and spawning adults. With no significant genetic differentiation among year classes despite varying recruitment dynamics, little evidence for chaotic genetic patchiness, and no truncation of adult genetic diversity in subsequent juvenile cohorts, there was little support for large variation among individual in reproductive success contributing to a low N e/N ratio. In fact, the consistent lack of significant differences in annual recruitment classes indicated that reproductive success among individuals was resistant to skewing. Among the various evolutionary forces that may be affecting N e, changes to demography due to fishing pressure are posited as a likely mechanism affecting current levels of genetic variation.