Winter Habitat of Juvenile Dolly Varden in the Canning River

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In the Arctic, rivers often freeze all the way to the bottom each winter leaving fish with limited habitat where they can survive. 

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The number of fish living in Alaska’s Arctic rivers is thought to be capped by the availability of freshwater that does not freeze as ice creating overwintering habitat. This project is specifically focused on identifying places where young Dolly Varden char (Salvelinus malma; also called Arctic char or Iqalukpik) overwinter. Large springs in the Brooks Range are key spawning and overwintering habitat for adult char, but the smaller, younger fish may need to avoid these areas so that hungry adults do not eat them. At the same time, char cannot survive in the ocean’s cold winter temperatures. Thus, we expect that young fish seek out deeper pools or areas with small springs in the lower reaches of the river that provide pockets of overwintering habitat separated by long stretches where the river is frozen to the bottom. We will visit areas that might provide pockets of overwinter habitat in the Canning River in late winter (April) to record fish presence/absence with minnow traps, small mesh nets, hook and line sampling, and an underwater video camera. By identifying the specific places where young Dolly Varden char overwinter, managers will have more information on locations important to the population of Dolly Varden char in making decisions on human activities in and around the river.  

In the Arctic, rivers are often thought to freeze completely during winter. Since fish need liquid water to survive, there are few places where they can live. Fish usually inhabit deep river channels and areas where springwater enters a stream. However, this video shows that winter habitat occurs in places we didn't expect, below the ice in the delta of a shallow river. 
Vanessa von Biela, USGS (Public domain.)

All photo credits below: Randy J. Brown, USFWS. Public domain.

Canning River with Brooks Range in the background

Canning River with Brooks Range in the background.

Michael Carey and Vanessa von Biela on Canning River

Michael Carey and Vanessa von Biela on the Canning River.

Canning River with bars view

Canning River with bars.

Canning River with bars

Canning River with bars.

 

Vanessa von Biela with cut bank at Canning River

Vanessa von Biela with cut bank at Canning River.

 

Hole in the ice from an auger

Hole in the ice from an auger.

Lowering minnow trap to fish

Lowering minnow trap to fish.

Minnow trap in icehole

Minnow trap in icehole.