Climate Change Decreases in Global Fisheries Production Vary by Size And Functional Type

Global climate change is expected to impact ocean ecosystems through increases in temperature, changes in mixing and stratification, and decreases in pH, oxygen, and primary production. These impacts propagate up through the food chain leading to amplified effects on higher trophic levels, but with disproportionate effects across species. To investigate how climate change will alter global fish assemblages and productivity, we used a spatially explicit mechanistic model of three fish functional types (FEISTY) coupled to an Earth System Model (GFDL-ESM2M) to make projections out to 2100. Since simulations under historical conditions highlighted ecologically meaningful sensitivities of metabolic parameterizations, we additionally explored the parameter uncertainty of future projections. Projections under a high emissions scenario (RCP 8.5) compared to mean contemporary simulations revealed strong increases in the ratio of pelagic zooplankton production to benthic production, a dominant driver of the abundance of large pelagic fish vs. demersal fish under historical conditions. Increases in this ratio led to shifts from benthic-based ecosystems towards pelagic-based ones. In combination with increased metabolic demands from higher temperatures, abundances of both types of large predatory fishes fell, resulting in more ecosystems dominated by forage fish. When integrated globally, all types of fish decreased, with large pelagic fish suffering the greatest declines and demersal fish having the highest degree of uncertainty. This study contributes a better understanding of future global changes in marine fisheries and highlights the importance of constraining size and temperature relationships with metabolism for reducing one aspect of uncertainty in 21^st century projections.