Spatial variation in potential and realized growth of juvenile Pacific cod in the southeastern Bering Sea

摘要

In the southeast Bering Sea, age-0 Pacific cod Gadus macrocephalus primarily occupy 2 distinct habitat types: shallow, coastal waters along the central Alaska Peninsula and surface waters over the broad continental shelf. We examined functional aspects of habitat use by describing regional and habitat-specific variation in feeding and growth energetics based on sampling conducted in late summer 2012. Diets varied among regions, with more benthic copepods, amphipods, and shrimps consumed in coastal regions and more pelagic copepods, krill, and pteropods consumed in surface waters over the shelf. Growth rates measured from otolith edge increments were highest along the Alaska Peninsula, the region supporting the highest density of age-0 cod. Interestingly, fish energetic condition was comparatively low in the region with the highest growth rates, suggesting a tradeoff between growth and energy storage. Water temperatures and prey energy densities were used with a bioenergetic model to derive spatially explicit estimates of growth potential. Growth potential was correlated with observed station-specific growth rates, providing an independent, empirical validation of the model. We also contrasted patterns of growth potential in 2012, a cold year in the Bering Sea, with those for 2005, a representative warm year. Growth potential was reduced in the warm year by up to 27%, and there was a shift in the region offering the highest growth potential. The observed thermally induced changes in growth potential, as well as the location of highest growth potential, may have significant implications for the recruitment of this important resource species under episodic or prolonged warming.