Conceptual model of energy allocation in walleye pollock (Theragra chalcogramma) from age-0 to age-1 in the southeastern Bering Sea

Abstract

Walleye pollock (Theragra chalcogramma) support the largest commercial fishery in the United States and are an ecologically important component of the southeastern Bering Sea (SEBS) pelagic ecosystem. Alternating climate states influence the survival of walleye pollock through bottom-up control of zooplankton communities and possible top-down control of predator abundance. Quantifying the seasonal progression and spatial trends in energy content of walleye pollock provides critical information for predicting overwinter survival and recruitment to age-1 because age-0 walleye pollock rely on energy reserves to survive their first winter. Age-0 and age-1 walleye pollock were collected in the SEBS from May to September 2008–2010. Energetic status was determined through quantification of energy density (kJ/g) and proximate composition (i.e., % lipid, % moisture) with variation in energy density primarily driven by variability in % lipid. Energy densities remained relatively low during the larval phase in spring, consistent with energy allocation to somatic growth and development. Lipid acquisition rates increased rapidly after transformation to the juvenile form (25–40mm standard length), with energy allocation to lipid storage leading to higher energy densities in late summer. This transition in energy allocation strategies is a physiological manifestation of survival constraints associated with distinct ontogenetic stages; a strategy favoring growth to escape size-dependent predation appears limited to larval development while juvenile fish allocate proportionally more mass to lipid storage in late summer. We propose that the time after the end of larval development and before the onset of winter represents a short critical period for energy storage in age-0 walleye pollock, and that overwinter survival depends on accumulating sufficient stores the previous growing season and consequently may be an important determinant of recruitment success.