Forecasted Shifts in Thermal Habitat for Cod Species in the Northwest Atlantic and Eastern Canadian Arctic

Abstract

Climate change will alter ecosystems and impose hardships on marine resource users as fish assemblages redistribute to habitats that meet their physiological requirements. Marine gadids represent some of the most ecologically and socio-economically important species in the North Atlantic, but face an uncertain future in the wake of rising ocean temperatures. We applied CMIP5 ocean temperature projections to egg survival and juvenile growth models of three northwest Atlantic coastal species of gadids (Atlantic cod, Polar cod, and Greenland cod), each with different thermal affinities and life histories. We illustrate how physiologically based species distribution models (SDMs) can be used to predict habitat distribution shifts and compare vulnerabilities of species and life stages with changing ocean conditions. We also derived an integrated habitat suitability index from the combined surfaces of each metric to predict areas and periods where thermal conditions were suitable for both life stages. Suitable thermal habitat shifted poleward for the juvenile life stages of all three species, but the area remaining differed across species and life stages through time. Arctic specialists like Polar cod are predicted to experience reductions in suitable juvenile habitat based on metrics of egg survival and growth potential. In contrast, habitat loss in boreal and subarctic species like Atlantic cod and Greenland cod may be dampened due to increases in suitable egg survival habitats as suitable juvenile growth potential habitats decrease. These results emphasize the need for mechanistic SDMs that can account for the combined effects of changing seasonal thermal requirements under varying climate change scenarios.

Predicting Pacific cod spawning habitat in a changing climate

“…However, in our case, it seems that the area currently predicted to be thermally suitable for Pacific cod is not larger than the current areas of known spawning. Thus, Pacific cod spawning activity will largely depend on movement and behavior across these emerging thermal habitats (Ciannelli et al, 2015;Cote et al, 2021;Dahlke et al, 2018). Despite our finding of an overall increase in the availability of suitable spawning habitat, we also found that sites historically suitable for spawning are not projected to be so by the end of the century.…”

“…Changes in thermal habitat for earlier life stages, as well as their effects, are less well documented. For gadids specifically, both increases and decreases in suitable spawning habitat with warming (based on experimentally-derived relationships between temperature egg survival as used here) have been found, with differences attributed to the nature of the temperature changes and life histories of the individual species (i.e., subarctic vs. arctic species, shape of the thermal response curve, nature of temperature changes in the region; Cote et al, 2021;Dahlke et al, 2018;Laurel & Rogers, 2020). For Polar cod, an arctic species with egg survival highest in waters < 3˚C, spawning habitat suitability is projected to decrease in both the Norwegian Sea (by ~67% in the warmest areas) and in the Labrador Sea and Northwest Atlantic (by ~21%) by the end of the century (Cote et al, 2021;Dahlke et al, 2018).…”

“…For gadids specifically, both increases and decreases in suitable spawning habitat with warming (based on experimentally-derived relationships between temperature egg survival as used here) have been found, with differences attributed to the nature of the temperature changes and life histories of the individual species (i.e., subarctic vs. arctic species, shape of the thermal response curve, nature of temperature changes in the region; Cote et al, 2021;Dahlke et al, 2018;Laurel & Rogers, 2020). For Polar cod, an arctic species with egg survival highest in waters < 3˚C, spawning habitat suitability is projected to decrease in both the Norwegian Sea (by ~67% in the warmest areas) and in the Labrador Sea and Northwest Atlantic (by ~21%) by the end of the century (Cote et al, 2021;Dahlke et al, 2018). Atlantic cod, a subarctic species whose eggs have a broader range of temperatures suitable for survival compared to both Polar and Pacific cod (highest survival between 0˚ and 9˚C), can expect regional increases and decreases in suitable spawning habitat by the end of the century (Cote et al, 2021;Dahlke et al, 2018).…”

“…Finally, we trimmed the projection simulations (CESM, GFDL, MIROC) to 2021 -2099. Global climate models -and thus regionally downscaled models driven by global models -can show systematic mismatches between their output and real-world values stemming from a variety of different factors, including coarse resolution, simplified processes, and imperfect understanding of physical and ecosystem processes (Cote et al, 2021;Hawkins et al, 2013). A small bias in simulated bottom temperature could strongly impact our projections of present-day and future habitat suitability due to the narrow, fixed thermal range that defines this habitat.…”

“…The effect of temperature on organismal physiology is not static across the lifespan of an individual, and thus, thermal limits and tolerance typically change with size and ontogeny (Brown et al, 2016;Dahlke et al, 2020;McKenzie et al, 2020). These changes in thermal sensitivities translate into uneven shifts in habitat use and distribution across life stages (Barbeaux & Hollowed, 2018;Cote et al, 2021;Drost et al, 2016). In particular, developing embryos and spawners are thought to exhibit the narrowest thermal tolerances, resulting in a tight relationship between spawning habitat and temperature (Dahlke et al, 2018(Dahlke et al, , 2020Pörtner, 2021).…”