Research Document - 2001/092

Overwintering habitat of juvenile Dolly Varden
(Salvelinus malma)(W.) in the Rat River, NT,
as determined by radio telemetry.

By S.J. Sandstrom, C.B. Chetkiewicz and L.A. Harwood

Abstract

In late-September 1995, a survey of the Rat River Dolly Varden (Salvelinus malma) stock was conducted by seining the various pools and riffle areas at the spawning and overwintering site on Fish Creek, a headwater tributary. Although this study determined the main overwintering location of the adult component of the population, it failed to find appreciable numbers of anadromous juvenile char (i.e., < 400 mm) at this site. In an attempt to determine where the juvenile component of the stock resides during the late-fall, and perhaps document whether additional overwintering habitat exists for this stock, sixteen anadromous juvenile char were radio tagged on August 26 and 27, 1996 near the mouth of the river, approximately 150 km downstream of the spawning/overwintering site. Four radio-tracking flights were made along the Rat River and the Fish Creek tributary on August 30, October 6, November 9, 1996 and March 20, 1997. Results of these tracking flights found that juvenile char use the same areas for overwintering as do the adult char, i.e., several deep pools just upstream of the aufeis field. However, unlike adults juvenile char do not move into these areas until well after freeze-up. Upon completing their upstream migration to the Fish Creek tributary by mid- to late-September juvenile char first occupy areas in Fish Creek within and below the main aufeis field. Final upstream movement into the overwintering pools above the main aufeis field likely does not occur until sometime in late November. It is speculated that this behaviour may be to avoid antagonistic interactions with the spawning adult char upstream. This region of the river may also provide better cover from predators and/or may provide an area of lower energy requirement prior to freeze-up.

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