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The western part of East/Japan Sea (WES) is an important area for understanding climate change processes and interactions between atmospheric and oceanic conditions. We analyzed the trends in recent oceanic conditions in the WES after the recent climate regime shift (CRS) that occurred in the late 1990s in the North Pacific. We explored the most important climate factors that affect oceanic conditions and determined their responses to changes in climate change. In the CRS that occurred in the late 1980s, changes in oceanic conditions in the WES were influenced by intensity changes in climate factors, and, in the late 1990s, it was by spatial changes in climate factors. The latitudinal shift of the Aleutian low (AL) pressure influences recent changes in oceanic and atmospheric conditions in the WES. The intensity of the Kuroshio Current and the sea level pressure in the Kuroshio extension region associated with the latitudinal shift of the AL pressure affects the volume of transport of the warm and saline water mass that flows into the WES and its atmospheric conditions. In addition, the fluctuations in the oceanic conditions of the WES affect various regions and depth layers differently, and these variations are evident even within the WES.

This study examined the dietary patterns of walleye pollock, Gadus chalcogrammus, off the middle eastern coast of Korea between January 2016 and December 2017 to determine the influences of various predictors on dietary changes. Based on stomach content analyses, walleye pollock was found to be a demersal carnivore that mainly consumes carid shrimps, euphausiids, mysids, teleosts, and cephalopods. The main prey species identified in the diets of walleye pollock were Euphausia pacifica (euphausiids), Themisto japonicus (amphipods), Neomysis spp. (mysids), Neocrangon communis, Pandalus borealis (carid shrimps), Watasenia scintillans (cephalopods), and Bothrocara hollandi (teleosts), which are hyper-benthic and bentho-pelagic organisms. Dietary analyses based on the weight contributions of different prey taxa to the diets revealed significant variations in dietary composition in terms of fish size, water depth, and season, implying intraspecific dietary segregation. Euphausiids dominate the diets of smaller individuals (