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Bottom temperature warming and its impact on demersal fish off the Pacific coast of northeastern Japan

Shigeho Kakehi*, Yoji Narimatsu, Yuriko Okamura, Asagi Yagura, Shin-ichi Ito

*Corresponding author:

ABSTRACT: Global climate change occurs not only at the ocean surface but also at the ocean bottom, which is the main habitat of demersal fish. To clarify the actual status of the bottom temperature warming off the Pacific coast of northeastern Japan, we examined gridded bottom temperature fields from 2003 to 2019 created by a newly developed gridding method using flexible Gaussian filter weighting with time, distance, and depth. The spatially averaged bottom temperature had a strong, significant warming trend of 0.083°C yr–1 to 0.115°C yr–1 in depth zones of 150–300 m, indicating bottom temperature warming. Corresponding to the warming, increases in landing amount were found in warm-water species such as searobin in the middle region of our study area (37°50’–39° N). The results of seasonal catch amounts suggested that ribbon fish and swimming crab recently began to overwinter and reproduce in the area. The distribution shifts of non-target species in fishery were also analyzed using bottom otter trawl survey data from the area from 2003 to 2019. Northward distribution shifts and increases in density were observed in blackbelly lantern shark and bighand grenadier, indicating that bottom temperature warming led to habitat expansion. Conversely, darkfin sculpin and jelly eelpout shifted northward with decreasing density, suggesting that bottom temperature warming had a negative effect on them. Deepsea bonefish shifted deeper into colder waters with increasing density and mean body weight. Thus, changes and responses of demersal fish to bottom temperature warming in the area were revealed.