Geographic variation in feeding of Pacific saury Cololabis saira in June and July in the North Pacific Ocean

Abstract

AbstractGut contents of Pacific saury Cololabis saira during their feeding migration through a transition zone between subtropical and subarctic waters in the North Pacific Ocean are reported. Geographic changes in feeding habits and preferences are described for the months of June and July, for the years 2012, 2016, and 2017. Pacific saury prey comprised 27 taxa. Cluster analysis based on numerical abundance of these prey taxa in guts indicated six Pacific saury feeding types (A to F) existed. Of these, types A–E occurred in low sea surface temperature waters (<ca 14°C). Gut content weight and gut fullness index were greater in types A, B, and E, with copepods Neocalanus plumchrus/flemingeri and/or N. cristatus contributing highly to carbon‐base weight. Although small euphausiids occurred in guts, guts were also often empty, suggesting feeding was less active at higher sea surface temperatures (>ca 14°C). Feeding patterns reveal N. plumchrus/flemingeri tended to be important prey species in areas west of ca 175°E, whereas Pacific saury feed mainly and selectively on N. cristatus in eastern areas, indicating a longitudinal difference in the trophic pathway from zooplankton prey to Pacific saury. These spatial differences in trophic pathways improve our understanding of nutritional intake in the commercially important Pacific saury during its feeding migration, and the effects this might have on fish size and weight, and associated commercial value.