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Marine Ecology and Stock Assessment Program

Spatial Distribution, Energetic Status, and Food Habits of Eastern Bering Sea Age-0 Walleye Pollock

figure 5, see caption
Figure 5.  Spatial distribution of log transformed catch per unit effort (fish/m3) for age-0 walleye pollock sampled in early autumn during warm (200405) and cool (200607) years in the eastern Bering Sea.

Age-0 walleye pollock were collected from the eastern Bering Sea during years when ocean temperatures were anomalously warm (200405) and cool (200607), see Figure 5 above. Variability in spatial distribution, food habits, energetic condition, and recruitment to the age-1 life stage was investigated in relation to thermal regime.

Age-0 walleye pollock were large in size and widely distributed during warm years, whereas they were small and largely confined to the middle domain of the eastern Bering Sea during cool years. Energy density was positively correlated with body weight and was greater during years when conditions were anomalously cool.

The proportion of smaller age-0 walleye pollock in the diet of larger individuals was high when conditions were warm (21.9% of diet by weight), and euphausiids were the most important prey (36.5% of diet by weight) when conditions were cool.

Eastern Bering Sea age-0 walleye pollock were abundant and broadly distributed from Bristol Bay to offshore and northern locations during warm years; during cool years, age-0 fish were less abundant, and their distribution was constricted to the southeastern Bering Sea. An inverse relationship between brood year abundance and survival from age-0 to age-1 was found.

Our results indicate that when spring/summer sea temperatures on the eastern Bering Sea shelf are very warm and when the water column is highly stratified during summer, age-0 walleye pollock allocate more energy to growth than to lipid storage, leading to low energy density before winter and thus to higher overwinter mortality.

By Jamal Moss

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