Comparative methods for evaluating climate change impacts on the foraging ecology of Alaskan groundfish

Climate change is expected to strongly impact Alaskan (USA) marine ecosystems, particularly those of the northern Bering Sea. To understand how climate change may alter predator demand for prey resources, we quantified the relationship between temperature and allometric rates of prey consumption for 3 major groundfish predators: walleye pollock Gadus chalco grammus, Pacific cod Gadus macrocephalus, and arrowtooth flounder Atheresthes stomias. We contrasted regional patterns in foraging rates of more than 120000 fish collected annually from 1981 to 2011 from the eastern Bering Sea (EBS), Gulf of Alaska (GOA), and Aleutian Islands (AI). From field observations, we estimate that juveniles and adults of each species eat 1.15 to 3.94 and 0.84 to 3.13 times their body weight (BW) yr(-1), respectively (i.e. 0.2 to 1.2% BW d(-1)), with arrowtooth in all 3 regions and adult EBS Pacific cod exhibiting the highest rates. If historical patterns signify future conditions, we estimate that a 2 degrees C projected increase in water temperature would cause 26 and 14% increases in daily rations of adult EBS pollock and Pacific cod, respectively, whereas we predict a 37% decline in the daily rations of EBS arrowtooth. Similarly, we predict that GOA pollock, Pacific cod and arrowtooth rations would increase markedly (70, 34, and 65%, respectively). Although daily ration of AI arrowtooth may increase by 31%, our models predict 41 and 3% declines in AI pollock and Pacific cod rations, respectively. These results portend (sometimes counterintuitively) region-and species-specific shifts in Alaska groundfish predator for aging rates and trophodynamic interactions concomitant with climate change.