Summer diet and feeding strategy of Pacific cod (Gadus macrocephalus) inhabiting the southern coast of Hokkaido, Japan

Abstract

The ontogenetic and interannual variations in the diet and feeding strategy of Pacific cod (Gadus macrocephalus) were examined based on 1,302 specimens collected by a trawling net off the southern coast of Hokkaido from late June to early July during 2016-2020. The diet comprised 63 species (13 taxa). Fish was the most important prey, followed by decapod crustaceans. In 2016, walleye pollock (Gadus chalcogrammus) was the dominant fish prey species, while amphipods, decapods, and Japanese lanternfish (Notoscopelus japonicus) were prominent in the diet in 2017.Japanese sardine (Sardinops melanostictus) were more predominant during 2018-2020. An ontogenetic comparison of diet indicated that smaller individuals (£ 400 mm standard length, SL) preyed mainly on small prey items, such as decapod crustaceans and polychaetes, whereas larger individuals (> 400 mm SL) preyed mainly on fish. Moreover, prey size exhibited a significant increasing trend with predator body length. These results suggest that Pacific cod has a flexible feeding strategy that differs by life stage. The updated information on predator-prey relationships provided herein improves our understanding of energy flow in the marine ecosystem and could facilitate ecosystem-based fishery management strategies.

Marine heatwaves alter the nursery function of coastal habitats for juvenile Gulf of Alaska Pacific cod

“…Mysids dominated juvenile Pacific cod diet composition during the MHWs, and, in August 2015 and 2019, they were present in more than 75% of all individual fish stomachs. Although coastal GOA zooplankton communities are poorly characterized relative to the pelagic GOA 60 , 61 , our observed shifts in diet composition during MHWs may be reflective of changes to the nearshore given that Pacific cod are considered opportunistic predators 62 . In the southern California Current, mysid abundance increased during the 2014–2016 MHW 63 , and the similar increase of mysids in Pacific cod diet composition observed during GOA MHWs may be due to changes in their spatial, temporal, or depth distributions that increased their accessibility to juvenile Pacific cod.…”