# Combined stomach content and stable isotope analyses revealed variations in trophic ecology of pacific cod in the east sea

## TL;DR

This study used stomach content and isotope analysis to show how Pacific cod diets and feeding levels vary by location, season, and size in the East Sea.

## Contribution

The study provides new insights into how Pacific cod trophic ecology varies with location, season, and fish size in the East Sea.

## Key findings

- Pacific cod diets vary latitudinally, seasonally, and by size, with teleosts, cephalopods, and carid shrimps as key prey.
- Larger cod consume more teleosts and cephalopods in cold seasons, while smaller cod prefer carid shrimps and amphipods.
- Stable isotope values differ between northern and southern sites, with higher values observed in larger cod and at Hupo.

## Abstract

This study investigated changes in the dietary composition and trophic levels of Pacific cod (Gadus macrocephalus) using stomach content and stable isotope analyses. Pacific cod samples were collected seasonally from May 2018 to February 2022 using bottom gill nets at the northern (Ayajin) and southern (Hupo) sites of the East Sea along the Korean coast. The primary dietary components included teleosts, amphipods, carid shrimps, and cephalopods. Gravimetric dietary analysis revealed distinct latitudinal, seasonal, and size-related variations, with teleosts, cephalopods, carid shrimps, and euphausiids serving as the key prey items. During the cold season, teleosts constituted the major dietary components of the large-sized Pacific cod, whereas smaller individuals consumed more carid shrimps, amphipods, and euphausiids. In the warm season, large-sized individuals predominantly consumed cephalopods irrespective of location, whereas smaller individuals favored amphipods and euphausiids at Ayajin and carid shrimps at Hupo. Differences in stable isotope values (δ13C and δ15N) between Ayajin and Hupo, between size classes, indicated higher values in the Hupo and in large-sized individuals. Increased consumption of teleosts and cephalopods by larger Pacific cod led to enriched isotope values, whereas the contribution of carid shrimps elevated the trophic level at Hupo. This study provides comprehensive insights into the dietary variations and trophic levels of Pacific cod in response to changes in prey availability.

The online version contains supplementary material available at 10.1038/s41598-025-20151-1.