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

Abstract

Gut 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.

Extensive Marine Heatwaves at the Sea Surface in the Northwestern Pacific Ocean in Summer 2021

“…In fact, some studies have reported impacts of MHWs on lower trophic levels of marine ecosystems (e.g., [38,39]). Commercially important fisheries' resources include Japanese sardine Sardinops melanostictus and Pacific saury Cololabis saira, which utilize the northwestern Pacific waters around the focal area as a nursery ground in summer (e.g., [40,41]). Hence, for sustainable management of ecosystems in the northwestern Pacific Ocean, physical and biological studies are essential, not only to evaluate influences of the 2021 MHWs but also to project the influences of future MHWs on marine ecosystems.…”

Effects of oceanographic environment on the distribution and migration of Pacific saury (Cololabis saira) during main fishing season

“…Growth, feeding, distribution, and migratory patterns of Pacific saury are all affected by SST 29 – 31 . The geographic distributions and abundances of Pacific saury fishing stocks in the northwestern Pacific are strongly linked to sea temperatures 9 , 22 .…”

Reduced body weight of Pacific saury (Cololabis saira) causes delayed initiation of spawning migration

“…Important food sources for Pacific saury in summer are large copepods, especially Neocalanus spp. (Miyamoto et al, 2020;Odate, 1994). The biomass of Neocalanus copepods varies interannually (Tadokoro et al, 2005).…”

“…Hatched larvae and juveniles are transported east along the Kuroshio Extension (Oozeki et al, 2015), after which they migrate north from subtropical regions into subarctic Oyashio waters from May to July (Fukushima, 1979). There they feed on the abundant copepods which occur in those regions (Miyamoto et al, 2020; Odate, 1994). Subsequently, they commence spawning migration towards the west in August or September (Kakehi et al, 2020; Miyamoto et al, 2019).…”