Ocean warming differentially impacts demographics of marine fish with contrasting life histories in two large marine ecosystems

Phenotypic responses of marine fishes to environmental change can vary among species, particularly during life stages when individuals undergo rapid growth and development. We assessed environmental impacts on the length-at-age (size) of subadult Pacific cod Gadus macrocephalus , walleye pollock (pollock) G. chalcogrammus , and yellowfin sole (YFS) Limanda aspera in the Bering Sea and Gulf of Alaska (GOA) from 2008 to 2019. We hypothesized that temperature affects size, but that reduced spatial extent of suitable habitat for YFS and Pacific cod increases susceptibility to interannual environmental variability. We focused on a basin-scale lifetime thermal index (lifetime average sea surface temperature) since growth is cumulative and geographic locations prior to catch were unknown. We also compared temperature-associated variation in size with literature-based length at 50% maturity (L 50 ) to address whether static thresholds often used in stock assessments could be affected by environmental variability. Generalized additive model results indicated that warmer temperatures were primarily associated with larger size. However, pollock size was invariant among years compared to the other species, and had an inverse relationship with temperature in the GOA after age 1. Observed variation in lifetime temperatures was sufficient to alter the annual age at which fish reached L 50 . Size variation was greater at younger ages, particularly for YFS, but maturation at older ages dampened the effects of temperature variability on YFS maturity estimates. These results suggest that the influences of temperature on population demographics are shaped by life history and location, and could affect biological information used to inform fisheries management.