Northern fur seals’ migration follows food, currents
Northern fur seals haul out on San Miguel Island, California. Photo: NOAA Fisheries/ Kristin Wilkinson.
New insights into the northbound migratory movement of northern fur seals (Callorhinus ursinus) were discovered through a collaborative study co-authored by a graduate student at the University of Hawai‘i at Mānoa and a Professor Emeritus at Hokkaido University, and led by the Wildlife Research Center of Kyoto University. The study, published recently in Deep-Sea Research Part I, revealed that the seals’ migration path is influenced by where they can find abundant prey and swift ocean currents.
“Specific seafloor features may concentrate prey resources and water temperature data suggest that animals may be foraging in the Kuroshio–Oyashio Transition Zone, where prey availability is high,” said Heping Li, lead author of the study and doctoral student at the Wildlife Research Center of Kyoto University.
“Seals also showed a high tendency to travel near the edges of anticyclonic eddies, where high-velocity regions may reduce travel cost,” added Ryo Dobashi, oceanography graduate student in the UH Mānoa School of Ocean and Earth Science and Technology.
“Our study filled key gaps in understanding the northbound migration of juvenile and young adult male northern fur seals along the Sea of Japan coast of southern Hokkaido,” said Li. “These findings enhance our understanding of how fur seals respond to oceanographic conditions during this critical phase of their annual life cycle.”
Long-distance migrators
Northern fur seals are long-distance migrators, moving seasonally between breeding colonies in the north and wintering grounds in the south. This seasonal migration allows them to avoid sea ice and harsh conditions in northern waters while relocating to ice-free areas where they can access abundant prey and restore their energy for the next breeding season. These seals are frequently observed along the Sea of Japan coast near southern Hokkaido and have been reported to damage fishing gear, remove catch directly from the net, and potentially compete with local fisheries.
Although the southward migration has been relatively well-documented, their northbound migration to breeding colonies, which begins in spring, remains poorly understood due to challenges such as tag loss, limited battery life, and the difficulty of capturing animals at sea. As fisheries damages in this region draw increasing concern, understanding northern fur seals movements and habitat use during this period is essential.
In the study, researchers collected satellite tracking data from juvenile and subadult male fur seals to investigate their northbound migration routes and behavioral responses to oceanographic features during their return trip to breeding colonies.
Movement patterns revealed two distinct phases: in the stay phase, south of 43° N, seals exhibited slower movements with frequent course changes, while in the northbound transit phase, when they were north of 43° N, their movement became faster and more directed. Results revealed that foraging activity was concentrated along continental shelf-breaks and within particular temperature ranges (8–13 ° C).
Future changes in response to climate
“As top marine predators, fur seals may shift their distribution and habitat use in response to environmental changes driven by climate variability and human activities,” said Li. “These shifts could lead to increased competition with coastal fisheries and with other marine predators for shared resources. Long-term monitoring is essential to understand how these top marine predators interact with changing ocean environments and to support sustainable marine ecosystem management.”
Additional authors of the study are Professor Yoko Mitani at the Wildlife Research Center of Kyoto University and Professor Emeritus Humio Mitsudera at Hokkaido University.
Read also on Kyoto University News and UH News.