Case Report: Oceanic migratory behavior of chum salmon in the summer Bering Sea using a pop-up satellite archival tag

Background The Bering Sea is a key foraging habitat for Pacific salmon, but their migration ecology remains poorly understood due to the region’s remoteness. Chum salmon ( Oncorhynchus keta ) is one of the most abundant Pacific salmon species, and spends much of its life in the open ocean. To obtain preliminary information on its migration ecology, we deployed a pop-up satellite tag (PSAT) on a chum salmon (fork length: 530 mm; ocean age: 3) captured and released in the central region (56.0°N, 174.9°W). Results The PSAT surfaced 75 days later in the North Pacific Ocean, near the waters off Amchitka Island in the Aleutians (50.8°N, 179.3°E), transmitting depth, water temperature, light, and acceleration-based activity data. From 65 days post-release, the PSAT recorded sea surface temperatures above 20°C, implying predation by an endothermic fish. The estimated track indicated a southward movement within the Bering Sea, suggesting it continued foraging migration. The fish predominantly occupied surface waters (above 10 m) but occasionally dived below the thermocline (deeper than 40 m). No consistent diel vertical migration was observed; however, increased activity was detected during twilight and in dives occurring during the daytime and twilight periods, potentially linked to foraging behavior. Conclusion This pilot case study provides the first documentation of chum salmon migrating in the summer Bering Sea over a two-month period and new insights into their open-ocean behavior, such as crepuscular activity. However, further study with additional individuals is required to explore the variation and consistency of these patterns.