Lake Erie walleyes Sander vitreus support important fisheries and have been managed as one stock, although preliminary tag return and genetic analyses suggest the presence of multiple stocks that migrate among basins within Lake Erie and into other portions of the Great Lakes. We examined temporal and spatial movement and abundance patterns of walleye stocks in the three basins of Lake Erie and in Lake St. Clair with the use of tag return and sport and commercial catch-per-unit effort (CPUE) data from 1990 to 2001. Based on summer tag returns, western basin walleyes migrated to the central and eastern basins of Lake Erie and to Lake St. Clair and southern Lake Huron, while fish in the central and eastern basins of Lake Erie and in Lake St. Clair were primarily caught within the basins where they were tagged. Seasonal changes in sport and commercial effort and CPUE in Lake Erie confirmed the walleye movements suggested by tag return data. Walleyes tagged in the western basin but recaptured in the central or eastern basin of Lake Erie were generally larger (or older) than those recaptured in the western basin of Lake Erie or in Lake St. Clair. Within spawning stocks, female walleyes had wider ranges of movement than males and there was considerable variation in movement direction, minimum distance moved (mean distance between tagging sites and recapture locations), and mean length among individual spawning stocks. Summer temperatures in the western basin often exceeded the optimal temperature (20-238C) for growth of large walleyes, and the

Eco-genetic individual-based models involve tracking the ecological dynamics of simulated individual organisms that are in part characterized by heritable parameters. We developed an eco-genetic individual-based model to explore ecological and evolutionary interactions of fish growth and maturation schedules. Our model is flexible and allows for exploration of the effects of heritable growth rates (based on von Bertalanffy and biphasic growth patterns), heritable maturation schedules (based on maturation reaction norm concepts), or both on individual- and population-level traits. In baseline simulations with rather simple ecological trade-offs and over a relatively short time period (<200 simulation years), simulated male and female fish evolve differential genetic growth and maturation. Further, resulting patterns of genetically determined growth and maturation are influenced by mortality rate and density-dependent processes, and maturation and growth parameters interact to mediate the evolution of one another. Subsequent to baseline simulations, we conducted experimental simulations to mimic fisheries harvest with two size-limits (targeting large or small fish), an array of fishing mortality rates, and assuming a deterministic or stochastic environment. Our results suggest that fishing with either size-limit may induce considerable changes in life-history trait expression (maturation schedules and growth rates), recruitment, and population abundance and structure. However, targeting large fish would cause more adverse genetic effects and may lead to a population less resilient to environmental stochasticity.

Fish maturation schedules vary greatly among systems and over time, reflecting both plastic and adaptive responses to ecosystem structure, physical habitats, and mortality (natural and fishing). We examined maturation schedules of commercially exploited lake whitefish (Coregonus clupeaformis) in the Laurentian Great Lakes (Lakes Michigan, Huron, and Superior) by estimating ages and lengths at 50% maturity, age-specific maturity ogives (age-specific probability of being mature), and probabilistic maturation reaction norms (PMRNs; a metric that accounts for effects of growth and mortality). Collectively, these estimates indicated variation in maturation schedules between sexes (i.e., males tend to mature at younger ages and shorter lengths than females) and among systems (midpoint estimates of PMRNs were smallest for Lake Michigan fish, intermediate for fish in the main basin of Lake Huron, and largest for fish in Lake Huron's Georgian Bay and Lake Superior). Temporally, recent increases in age at 50% maturity in Lakes Huron and Michigan may primarily reflect plastic responses to decreased growth rates associated with ecosystem changes (e.g., declines of the native amphipod, Diporeia spp.). As plastic and adaptive changes in maturation schedules of fish stocks may occur simultaneously and require different management considerations, we recommend the concomitant analysis of multiple maturation indices.Résumé : Les calendriers de maturation des poissons varient considérablement dans le temps et d'un système à un autre, ce qui reflète à la fois leurs réactions plastiques et adaptatives à la structure de l'écosystème, aux habitats physiques et à la mortalité (naturelle et due à la pêche). Nous examinons les calendriers de maturation des grands corégones (Coregonus clupeaformis) exploités commercialement dans les Grands Lacs laurentiens (lacs Michigan, Huron et Supérieur) en estimant les âges et les longueurs à 50 % de maturité, les ogives de maturité spécifiques à l'âge (probabilité d'être mature en fonction de l'âge) et les normes de réaction probalistes de maturation (PMRNs, une métrique qui tient compte de la croissance et de la mortalité). Dans leur ensemble, ces estimations indiquent qu'il y a une variation des calendriers de maturation entre les sexes (c'est-à-dire que les mâles tendent à arriver à maturité à un âge et une longueur inférieurs à ceux des femelles) et selon les systèmes (les estimations médianes des PMRNs sont plus basses au lac Michigan, intermédiaires chez les poissons du bassin principal du lac Huron et maximales chez les poissons de la baie Georgienne du lac Huron et ceux du lac Supérieur). À l'échelle temporelle, les accroissements récents de l'âge auquel 50 % des poissons sont matures dans les lacs Huron et Michigan peuvent représenter principalement des réactions plastiques à la diminution des taux de croissance associée aux changements dans les écosystèmes (par ex., le déclin des amphipodes indigènes Diporeia spp.). Puisque les changements plastiques et adaptatifs dans les calendriers de ma...