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.