Warming leads to opposite patterns in weight-at-age for young versus old age classes of Bering Sea walleye pollock

Abstract

The temperature–size rule predicts that climate warming will lead to faster growth rates for juvenile fishes but lower adult body size. Testing this prediction is central to understanding the effects of climate change on population dynamics. We use fisheries-independent data (1999–2019) to test predictions of age-specific climate effects on body size in eastern Bering Sea walleye pollock ( Gadus chalcogrammus). This stock supports one of the largest food fisheries in the world but is experiencing exceptionally rapid warming. Our results support the predictions that weight-at-age increases with temperature for young age classes (ages 1, 3, and 4) but decreases with temperature for old age classes (ages 7–15). Simultaneous demonstrations of larger juveniles and smaller adults with warming have thus far been rare, but pollock provide a striking example in a fish of exceptional ecological and commercial importance. The age-specific response to temperature was large enough (0.5–1 SD change in log weight-at-age) to have important implications for pollock management, which must estimate current and future weight-at-age to calculate allowable catch, and for the Bering Sea pollock fishery.