Eco-Genetic Modeling to Investigate Life History Trade-Offs for Exploited Migratory Fishes

Many animals undertake long distance migrations to enhance growth, survival and reproduction opportunities. Migration may be energetically costly for many fishes, and long distance migrations, in particular, may constrain growth and/or reproduction of fishes, leading migratory fish to cope with such constraints through life history trade-offs. We investigate migration-induced life history trade-offs; e.g., (non-exclusively) skipped spawning, delayed maturity, and reproductive investment, using an individual-based, eco-genetic modeling approach. We build a virtual population model, comprised of numerous individuals with heterogeneous phenotypes and genotypes. Based on evolutionary theory (reaction norm models), we design genetic codes for growth and maturation traits of individuals, and impose density-dependent effects on growth so that individual growth and maturation are determined both genetically and plastically. We used the model to conduct experimental simulations, evaluating the effects of varying migratory energy costs on growth and reproduction life history trade-offs and population vital rates. Moreover, we evaluate how such trade-offs respond to differential size-selective mortality schedules (i.e., approximating fisheries harvest). Simulation results should inform our understanding of life-history patterns and management strategies for diverse migratory species, including several highly valuable tunas and billfish.