Methodological challenges to examining the causes of variation in stock reproductive potential

Understanding the causes of variation in stock reproductive potential (SRP) is challenging due to the difficulty in assessing the relative contribution of environmental, demographic and genotypic influences. This review explores how experimental and comparative field studies have been used to disentangle sources of variation in maturity, fecundity and the timing of spawning. By comparing reproductive parameters and corresponding environmental conditions among stocks of a species it is clear that demography, energetic state and temperature are important factors affecting variation in SRP. Common garden and environment experiments have confirmed that there is also a substantial genetic component to regional differences in reproductive investment and timing of spawning. Environmental manipulation experiments have helped to elucidate the proximate mechanisms underlying many reproductive processes. Together these different sources of information have provided a foundation for the development of statistical and individual based modelling approaches that help explain variation in SRP. In the near future, genomic investigations may provide a direct means to account for genetic influences on reproductive variation. Given that the age and size structure of many fish stocks has become truncated through fishing, a greater focus on the contribution of reproductive life span to SRP is also needed.