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The present study examines vertical distributions of the early life stages of walleye pollock (Theragra chalcogramma) in the Southeastern Bering Sea to assess ontogenetic and diel vertical migration in relation to development and habitat. Walleye pollock demonstrated a decrease in the depth of occurrence following hatching, indicating an ontogenetic change in vertical distribution. Eggs occurred deepest in the water column and early juveniles occurred shallowest. Vertical distributions were related to the date of collection, water column depth, and thermocline depth. Non-feeding stages (eggs and yolksac larvae

Fishery managers require an understanding of how climate influences recruitment if they are to separate the effects of fishing and climate on production. The southeastern Bering Sea offers opportunities to understand climate effects on recruitment because inter-annual oscillations in ice coverage set up warm or cold conditions for juvenile fish production. Depth-averaged temperature anomalies in the Bering Sea indicate the past nine years have included three warm (2003–2005), an average (2006), and five cold (2007–2011) years. We examined how these climatic states influenced the diet quality and condition (size, energy density and total energy) of young-of-the-year (YOY) pollock (Theragra chalcogramma) in fall. The implications of fall condition were further examined by relating condition prior to winter to the number of age-1 recruits-per-spawner the following summer (R/S). The percentage of lipid in pollock diets was threefold higher in cold years compared with warm years, but stomach fullness did not vary. Consequently, fish energy densities were 33% higher in cold years (P

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 (25-40 mm 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.

A multispecies approach was used to examine the role of the canopy forming kelp, Nereocystis luetkeana , in structuring kelp communities near Juneau, Alaska (58°22′53 N, 134°38′45 W). Large-scale (1500 m 2 ) manipulations were used to test direct and indirect effects of Nereocystis on faunal assemblages. Fish and invertebrate abundances were quantified in relation to canopy (canopy, no canopy), depth (bottom, surface), and season (summer, winter) using Standard Monitoring Units for Recruitment of Fish (SMURFs), light traps, and visual surveys. Lacuna vincta directly utilized the canopy of Nereocystis with greatest abundances at canopy sites during the summer. In contrast, a direct negative effect of Nereocystis was observed for schooling Gadidae fishes; six times more fish were observed at sites without canopy kelp. The abundance of juvenile benthic fishes was twice as high at the bottom of sites containing Nereocystis as compared to no canopy sites, providing strong evidence for an indirect effect of canopy presence on community structure. Other invertebrate abundances (i.e., amphipods, copepods) were greater within the bottom strata (sub-canopy) of all sites, regardless of canopy or season. Our results illustrate the importance of a multispecies approach and present novel information for a little-studied, high-latitude kelp system.

Understanding mechanisms behind variability in early life survival of marine fishes through modeling efforts can improve predictive capabilities for recruitment success under changing climate conditions. Walleye pollock (Theragra chalcogramma) support the largest single-species commercial fishery in the United States and represent an ecologically important component of the Bering Sea ecosystem. Variability in walleye pollock growth and survival is structured in part by climate-driven bottom-up control of zooplankton composition. We used two modeling approaches, informed by observations, to understand the roles of prey quality, prey composition, and water temperature on juvenile walleye pollock growth: (1) a bioenergetics model that included local predator and prey energy densities, and (2) an individual-based model that included a mechanistic feeding component dependent on larval development and behavior, local prey densities and size, and physical oceanographic conditions. Prey composition in late-summer shifted from predominantly smaller copepod species in the warmer 2005 season to larger species in the cooler 2010 season, reflecting differences in zooplankton composition between years. In 2010, the main prey of juvenile walleye pollock were more abundant, had greater biomass, and higher mean energy density, resulting in better growth conditions. Moreover, spatial patterns in prey composition and water temperature lead to areas of enhanced growth, or growth ‘hot spots’, for juvenile walleye pollock and survival may be enhanced when fish overlap with these areas. This study provides evidence that a spatial mismatch between juvenile walleye pollock and growth ‘hot spots’ in 2005 contributed to poor recruitment while a higher degree of overlap in 2010 resulted in improved recruitment. Our results indicate that climate-driven changes in prey quality and composition can impact growth of juvenile walleye pollock, potentially severely affecting recruitment variability.