Modeling approaches suggest that changes in species abundance and density within MPAs can be complex and may alter the dynamics of individual somatic growth rates. Individual growth rates within and outside of MPAs must be quantified to gain a more complete picture of how the management protections of MPAs affect overall abundance, biomass and individual growth – traits that in turn impact population dynamics like recruitment and mortality. This project will evaluate the efficacy of measuring plasma concentrations of the hormone insulin-like growth factor-1 (IGF-I) as a non-lethal, physiological approach for quantifying growth rate and nutritional status of marine fishes. First, the scientists will test the validity of IGF-I as a growth biomarker in laboratory-reared juvenile black rockfish. The researchers will then sample wild black rockfish and lingcod within and outside of two MPAs (Point Buchon and Piedras Blancas) to determine if there is variation in plasma IGF-I concentrations based on habitat protection status. If successful, this method may provide a new, cost-effective approach for assessing the growth rate of individuals in wild populations that is superior to the current capture-mark-recapture method.