Annual Changes in the Feeding Ecology of Blackfin Flounder (Glyptocephalus stelleri) in the East Sea of Korea

A total of 3930 blackfin flounder (Glyptocephalus stelleri) individuals were collected continuously on a monthly basis from the East Sea of Korea in 2024 (n = 1800) and 2025 (n = 2130). The total length ranged from 10.6 to 44.0 cm in 2024 and from 11.9 to 49.7 cm in 2025. The major prey items differed between the years. In 2024, polychaetes (75.3%) and amphipods (12.2%) were the dominant prey items, whereas in 2025, euphausiids (33.1%), polychaetes (33.7%), and fish (17.5%) were the most important prey groups, indicating a clear interannual variation in diet composition. PERMANOVA revealed that diet composition varied significantly with year, season, and size class (p < 0.05), with a significant interaction between the year and season. These patterns were consistently supported by the CAP ordination, which showed a clear separation of samples along the seasonal gradient on the CAP1 axis, with additional variations associated with the year and size class observed within the respective seasonal groupings. Ultimately, these results suggest that G. stelleri functions as an opportunistic feeder that is capable of shifting its diet in response to environmental fluctuations. This study aims to provide scientific data for efficient fishery resource management and ecosystem-based assessments in response to future climate change.