Hatch timing and growth of juvenile polar cod (Boreogadus saida) in a warming Arctic: insights into overwinter survival potential

Abstract

Polar cod ( Boreogadus saida ) is a widespread, cold-adapted fish that plays a central role in Arctic food webs. Rising temperatures, declining sea ice, and associated changes in ecosystem dynamics may threaten this species. We investigated the influence of temperature on the pre-winter size of juvenile polar cod (an important predictor of overwinter survival and recruitment), examining hatch timing and growth across warm and cold years in the Chukchi Sea. Otolith-based estimates of age and growth showed that juveniles collected in warm years were generally larger and older, but detected no significant differences in size-at-age or recent growth (7 days prior to capture ). Recent growth was inversely related to mean water column temperature early in the sampling season, a trend that decoupled later in the year. Temperature at catch explained little of the observed variation in growth, suggesting that the expected positive influence of temperature on growth was likely mediated by covarying oceanographic and ecological shifts. Ultimately, multiple environmental factors influenced final pre-winter size, with variation driven more by hatch phenology and an extended growing season, than by accelerated somatic growth rates.

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