Climate predictions of marine fish
Global climate model simulations of marine fish typically project declines in fish community biomass ranging between 5 to 15% depending on the climate scenario (Tittensor et al. 2021). Most of these fish community models have a temperature scaling of metabolic and feeding rates that is approximately doubled each 10°C increase (Q 10 of 2). Since fish community biomass is inversely related to the effect of temperature on individual rates, biomass declines as temperature increases. Both our SEM and trophodynamic model findings support this parametrization.
The above parametrization of metabolic and feeding rates is naturally a simplification of temperature effects on fish physiology. Studies have indicated that the temperature scaling of feeding rates is typically lower than the scaling of metabolic rates (Vucic-Pestic et al.2011; Rall et al. 2012), as implemented in some global fish models (Cheung et al. 2013; Petrik et al. 2019). The lower temperature scaling of feeding rates reduces the fraction of energy that is available for fish growth in warmer waters. As a consequence, average fish growth increases less along a temperature cline than the expected increase in metabolism (van Denderen et al. 2020). So far, it has been difficult to predict how such temperature scaling at the individual level translate to the overall community. Our empirical results provide evidence indicating that demersal community biomass is equally constrained by temperature.
We observed no changes in demersal fish biomass that were correlated with temperature over the time period of the survey data. Temperature and fisheries catch fluctuate in time and fish populations may have lagged responses to both. We therefore expect that the observed variations in temperature were too small to reveal a signal, at least during the study period. Other studies reporting changes in fish populations and communities under recent warming investigated species-specific responses in recruitment, productivity and/or distributional changes, as well as shifts in the trait-composition of the fish community (Pinsky et al. 2013; Frainer et al.2017; Free et al. 2019; Friedland et al. 2020). The latter are likely more sensitive to environmental changes than demersal community biomass, as these trait-based metrics account for changes in both composition and relative abundances of individual species.