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 wi nter flounder, Pleuronectes americanus, by means of an individual-base d simulation model, These factors were varied to approximate condition s at three latitudinally distinct sites in winter flounder's geographi c range from New Jersey, USA (southernmost site) to New Brunswick, Can ada (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 t han 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 s izes of recruits, larval and juvenile growth rates, larval period dura tion) due to each of the three manipulated factors and their interacti ons. Season duration explained most of the variation in the responses except for the sizes of recruits at year's end which was influenced mo st by the timing of prey production. Interaction effects of season dur ation and prey production were evident in all responses, reflecting th e importance to flounder recruitment of the phenology of prey producti on relative to flounder early life history. Even though mortality rate s were assigned as part of the factorial design structure, they accoun ted for only 10% of the variance in the number of recruits. These simu lation results are in need of empirical verification and we suggest wa ys to proceed. We also propose means of enhancing data on winter floun der life history and ecology, and methods for expanding our model and analysis. We conclude that our approach proved useful for 1. appraisin g 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 proce sses, and 3. identifying recruitment hypotheses that warrant further e mpirical evaluation.