Trophic ecology of Pacific cod Gadus macrocephalus off the southern and northeastern coasts of Hokkaido

概要

Feeding habits and nutritional condition of Pacific cod Gadus
macrocephalus were investigated based on the 1,893 specimens collected
in the waters off the southern coast of Hokkaido (SCH) during 2016–2020
and off the northeastern coast of Hokkaido (NCH) during 2018–2020. The
results of stomach contents analyses indicated that Pacific cod ingest a
variety of prey species, comprising 60 and 45 species in SCH and NCH,
respectively. Fish was the most important prey in SCH (95.3, %IRI;
relative important index) and NCH (68.6, %IRI), respectively. The
dominant fish prey were Japanese sardine Sardinops melanostictus in SCH
(36.7, %IRI) and walleye pollock Gadus chalcogrammus in NCH
(35.1, %IRI). Pacific cod also preyed highly on decapod crustaceans,
mainly snow crab Chionoecetes opilio (44.2, %IRI) in NCH. In SCH, the
predominance of walleye pollock in 2016 (48.5, %W; percentage of wet
weight) was replaced by Japanese sardine in 2018-2020 (36.3–65%, %W).
Such temporal and spatial variations in the diets suggest that Pacific cod is
a generalist and opportunistic feeder. The variation of prey species was
great in the cod measured 300–500 mm SL, whose main diet gradually
shifted from decapods to fish as they grow. The stomach fullness index was
higher in the individuals feeding on Japanese sardine (SCH) and walleye
pollock (NCH). ...

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