Study: Arctic fish expanding into new coastal habitats in Alaska
Study co-author with an Inconnu (or Sheefish) in the Kobuk River in Northwest Alaska
Katja Berghaus
Changing behavior of Inconnu highlight need to protect connected coastal and freshwater habitats
ANCHORAGE, AK (Nov. 10, 2026) A new study shows one of Alaska's iconic fish species is expanding into new coastal habitats hundreds of miles from its historical range.
Published in the journal Arctic Science, the study found that Inconnu, also known as Sheefish, appear to be expanding into new freshwater and coastal habitats in Northwest Alaska. Inconnu are increasingly being documented in rivers, lagoons and coastal waters outside their previously known range, with some fish traveling as much as 250 kilometers (about 155 miles) beyond their previously documented distribution. The study also found that all Inconnu exhibited diadromy—moving back and forth between freshwater and saltwater—and relied extensively on freshwater, estuarine and marine habitats throughout their lives.
The research team combined Traditional Ecological Knowledge shared by local subsistence fishers, long-term fish monitoring data, pop-up satellite archival tag information and chemical analysis of fish otoliths, or ear bones, to better understand how Inconnu use freshwater and coastal habitats throughout their lives. Inconnu are an important source of food for many Indigenous and rural communities in the region and their changing distribution may affect existing fish assemblages and could have implications for subsistence fisheries.
"Protecting Inconnu requires protecting entire watersheds and coastal ecosystems ... As development pressures intensify across the Arctic, conserving connectivity among these habitats will be increasingly important for sustaining subsistence fisheries." - Jason Leppi, Ph.D., study co-author
“Inconnu in Northwest Alaska are known to reproduce only in the Kobuk and Selawik Rivers watersheds. Individuals weighing up to 27 kg (60 lb) migrate annually from coastal feeding areas to spawn in the mainstem rivers before descending to estuarine overwintering areas. Maintaining water quality and watershed integrity across these intact ecosystems will help inconnu populations persist as Arctic conditions continue to change” said Jason Leppi, Ph.D., fisheries scientist for The Wilderness Society and co-author of the study.
In addition to the dramatic landscape changes occurring as a result of global climate change, proposed developments in the region, such as sulfide mining in the Ambler Mining district, within the headwaters of the Kobuk River watershed, present major risks to Inconnu populations. Mining activities have been shown to degrade watershed integrity and downstream cumulative impacts are an additional threat to migratory fishes.
"This study demonstrates that protecting Inconnu requires protecting entire watersheds and coastal ecosystems. Inconnu depend on rivers, estuaries, lagoons, and nearshore marine waters throughout their lives,” said Leppi. “As development pressures intensify across the Arctic, conserving connectivity among these habitats will be increasingly important for sustaining subsistence fisheries."
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