Modeling lipid mobilization and reproductive investment in lake trout using data derived from hatchery and field studies

Organisms allocate available energy to growth and reproduction to maximize fitness. Stochastic environments, combined with tradeoffs between different components of fitness, lead to phenotypic plasticity. We completed a four year study where our objective was to quantify the degree of phenotypic plasticity involved in lipid mobilization and egg-laying strategies in 4 stocks of lake trout. We used fish that originated from wild broodstock that were raised in common hatchery environment until maturity. We varied food rations across years, tracked lipid concentrations in the body using a non-invasive fatmeter, and collected eggs at spawning. Our results clearly suggest that stocks show lipid-fecundity relationships that fall along reaction norms. Field collections of wild fish from same stocks yielded life-history data that explained the shape of the reaction norms observed in hatchery data. Both field and hatchery data were modeled to predict fecundity from lipid concentration using age and population mortality as inputs. Our model is the first to predict fecundity in lake trout using both lipid concentrations and life history characteristics and is likely transferable to other stocks.  We also provide an easy, non-lethal method for estimating fecundity from wild lake trout which can have use in spawning stock assessment and restoration.