The importance of female phenotype in determining reproductive potential and recruitment in Atlantic coast striped bass (Morone saxatilis)

Abstract

The influence of female phenotype on the reproductive potential of Atlantic coast striped bass is addressed in three key areas of research. The importance of the environment in shaping maternal phenotype was evaluated using a spawning stock time-series to evaluate possible environmental drivers of female migration timing in the Chesapeake Bay. Results showed that local and recent water temperature was the primary factor influencing timing of movement onto spawning grounds, with higher temperatures resulting in early movements. Next, two approaches were used to evaluate the influence of female energetic condition on reproductive potential. First, a field approach was used to test the hypothesis that relative total female condition (hereafter condition) has a positive influence on pre-fertilized indicators of reproductive potential (i.e., probability of spawning, relative fecundity, and relative oocyte volume). Results indicated that condition had a positive influence on residual fecundity, residual oocyte volume and indirectly on the probability of spawning. In the second approach, a laboratory experiment was conducted to test the hypothesis that female condition has a positive effect on offspring size, growth and survival. The null hypothesis that the maternal influences on offspring phenotype did not differ in the Chesapeake Bay and Roanoke River populations also was tested. In contrast to the effects of female condition on pre-fertilized indicators of reproductive potential, condition had no influence on offspring phenotype in either population. Instead, post-spawn gutted weight alone had the greatest influence on offspring phenotype, although to a lesser and potentially insignificant degree in the Roanoke River.

Finally, a preliminary field evaluation was conducted in the Patuxent River, MD to determine whether maternal influences can lead to disproportionate numbers of mothers contributing to juvenile recruitment. Specifically, this study evaluated whether the variance in the distribution of half-sibling families was greater than expected by random reproductive success (i.e., Poisson process). If true, it was expected that the effective population size would be orders of magnitude smaller than the census size. Results provide preliminary evidence for higher than expected variance in reproductive success; however, methodological improvements will be necessary to confirm these results in the future