In addition, smaller rivers such as the Nowitna, Black, and Porcupine have small local populations. The Minto Flats and Upper Yukon River populations are year-round residents in the eastern part of Interior Alaska. The Lower Yukon and Kuskokwim groups overwinter in the delta areas of these large rivers while the Kobuk-Selawik groups spend the winter in the brackish waters of Hotham Inlet and Selawik Lake. These latter groups can best be termed estuarine anadromous. Upstream migrations of sheefish from the wintering grounds begin during the period of ice breakup.
Some fish move to feeding grounds while mature fish migrate to spawning areas.
The movements last from a few weeks in the Upper Yukon to over four months in the Lower Yukon River. Sheefish travel up to 1,000 miles upstream to spawn in the Alatna River. Sheefish do not feed in the later stages of the spawning migration but subsist on reserves of body fat. Sheefish have very stringent spawning ground requirements. The water must be from 4 to 8 feet deep with fast current over a bottom composed of differentially-sized gravel.