The contribution of diet to the dramatic reduction of the 2013 year class of Gulf of Alaska walleye pollock (Gadus chalcogrammus)

A survey-based time series (2001-2019) showed that age-0 walleye pollock (Gadus chalcogrammus) occurred in very high abundances in 2013 compared with other years; however, recruitment of the 2013 year class to age-1 was lower than average. Diet composition of age-0 fish was examined from the 2013 year class to assess the potential impact of the consumed prey on walleye pollock. High abundances of smaller age-0 fish were found at stations southwest of the Shumagin Islands compared with low abundances of larger fish found surrounding Kodiak Island. Fish in the southwest region showed a higher intake of low-quality food items such as pteropods and larvaceans compared with fish in the northwest region that had consumed mostly higher quality prey such as large copepods and euphausiids. Even though no significant differences were found in fish condition between regions overall, spatial differences in fish weight were found after accounting for sample day of year. Prey-specific Index of Relative Importance analysis showed southwest region fish had consumed a larger diversity of taxa, whereas fish from the rest of study area primarily consumed large copepods and euphausiids. These results suggest that high abundances of smaller pollock found in the southwestern part of the study region consumed a higher percentage of low-quality, lipid-poor prey taxa, which likely contributed to reduced overwinter survival and increased mortality.

Automated summary

A survey-based time series from 2001 to 2019 revealed that age-0 walleye pollock had high abundances in 2013, but their recruitment to age-1 was lower than average. The study found that fish in the southwest region consumed more low-quality food, while fish in the northwest region primarily consumed higher quality prey. These results suggest that the diet composition of prey may impact overwinter survival and mortality of walleye pollock.