Growth patterns of larval walleye pollock Gadus chalcogrammus from core and peripheral habitat differ in response to temperature

Walleye pollock (Gadus chalcogrammus) supports one of the world's largest fisheries and is a key species in North Pacific ecosystems. Its future as a sustainable fishery may be dependent on its ability to adapt to changing water temperatures under climate change. The largest global average increase in sea surface temperature has occurred in Alaska, and increasing temperatures are predicted. Here, we examined responses to a range of temperatures in the early life history of walleye pollock from a northern (core) and a southern (peripheral) part of their range using growth measurements and genetics (RADseq). Crosses were conducted to generate families with one female and three male adults from Shelikof Strait, AK and Puget Sound, WA. Offspring were reared to the late larval stage at three temperatures corresponding to low (1.5 °C), medium (5.8 °C), and high (∼12 °C) temperature relative to natural conditions. Alaska pollock outperformed Puget Sound pollock at the lowest temperatures, hatching earlier with a higher growth rate than Puget Sound pollock. At medium temperatures, Puget Sound and Alaska pollock grew at the same rate but Alaska pollock hatched sooner. The response to high temperatures was the same in both groups, characterized by early hatching at a small size and high growth rates. Genetic analysis did not show differences among family groups that survived different temperature treatments. Our results demonstrate local adaptation, although a link between genotype and phenotype was not found.