Recruitment and recruitment processes of winter flounder, Pleuronectes americanus, at different latitudes: Implications of an individual-based simulation model

We evaluate the joint effects of temperature, hours of daylight, prey production, spawning regimes, and mortality rates on recruitment of winter flounder, Pleuronectes americanus, by means of an individual-based simulation model, These factors were varied to approximate conditions at three latitudinally distinct sites in winter flounder's geographic range from New Jersey, USA (southernmost site) to New Brunswick, Canada (northernmost site). Most life historical and demographic response variables from simulation output differed substantially among sites. At year's end, the recruits were larger but fewer at lower latitudes than at higher ones. We further assessed the effects of season duration, prey production, and mortality rate on recruitment by means of a 3(3)-factorial numerical experiment. This analysis provided estimates of the proportion of variance in the response variables (the number and sizes of recruits, larval and juvenile growth rates, larval period duration) due to each of the three manipulated factors and their interactions. Season duration explained most of the variation in the responses except for the sizes of recruits at year's end which was influenced most by the timing of prey production. Interaction effects of season duration and prey production were evident in all responses, reflecting the importance to flounder recruitment of the phenology of prey production relative to flounder early life history. Even though mortality rates were assigned as part of the factorial design structure, they accounted for only 10% of the variance in the number of recruits. These simulation results are in need of empirical verification and we suggest ways to proceed. We also propose means of enhancing data on winter flounder life history and ecology, and methods for expanding our model and analysis. We conclude that our approach proved useful for 1. appraising multiple, interacting recruitment processes, 2. locating areas where incomplete knowledge of winter flounder life history and the habitat it occupies limits a more satisfactory assessment of recruitment processes, and 3. identifying recruitment hypotheses that warrant further empirical evaluation.