Reductions in body size of marine fishes linked to ocean warming have been reported across numerous ecosystem types and species. These smaller body sizes are in turn linked to lower population biomass and reproductive output, which have serious potential implications for future fisheries yield projections, stock assessments, and ecosystem stability. The underlying mechanisms for this pattern largely remain untested, but one theory that has gained traction is that reduced body sizes result from constraints on gill size. However, this theory is strongly debated, and there has not yet been empirical research to test this hypothesis.
To address this knowledge gap, this project tests the proposed mechanisms in a species of high value to California fisheries and ecosystems, the Pacific sardine. Specifically, the project team will (1) quantify the roles of oxygen limitation and gill surface area-body size relationships under variable temperatures; (2) examine relationships of energetic demands and life history trade-offs (i.e., timing and investment in growth vs. reproduction) related to temperature and reduced body sizes; (3) compare the roles of phenotypic plasticity and local adaptation in shaping population level responses to ocean warming.
The project aims to establish valid physiological mechanisms underlying current patterns that can be integrated into stock assessments and ecological models to predict climate change impacts on California fisheries yields and ecosystems under different management scenarios.