Temperature exposure in cod driven by changes in abundance

Animals actively select the most suitable habitat in terms of fitness, much of which is mediated by temperature. We reconstructed population abundance, oxygen isotope and temperature chronologies for the Icelandic and the Northeast Arctic (NEA) cod (Gallus morhua) populations to determine if their temperature selectivity over the last 100 years was driven by rising water temperatures and (or) changes in abundance. Individual annual growth increments from immature and mature life history stages of cod collected in southern Iceland and the Lofoten area (Norway) were micromilled from adult otoliths and then assayed for stable oxygen isotopes (delta O-18(oto)lith). Linear mixed effect models were used to identify and quantify the densitydependent temperature exposure of both cod populations. The results indicated that Icelandic cod migrated into warmer waters with increasing abundance (p < 0.05), whereas NEA cod moved into colder waters (p < 0.001). Our results suggest that thermal preferences and density-dependent effects can be used to forecast potential redistribution scenarios of fish as oceans warm.

Automated summary

Animals actively select suitable habitat based on fitness, with temperature playing a crucial role. This study reconstructed population abundance, oxygen isotope, and temperature chronologies for Icelandic and Northeast Arctic cod populations and found that Icelandic cod migrated towards warmer waters with increasing abundance, while NEA cod moved towards colder waters. These findings suggest that thermal preferences and density-dependent effects can help predict potential redistribution scenarios of fish as oceans warm.