Seasonal Movement of Dolly Varden and Cutthroat Trout with Respect to Stream Discharge in a Second-Order Stream in Southeast Alaska

Abstract

The relationship between the movement of small (<150-mm) Dolly Varden Salvelinus malma and cutthroat trout Oncorhynchus clarkii and stream discharge is not well known in streams of southeast Alaska. We measured movement in a small headwater stream using passive integrated transponder (PIT) tags and stationary antennas to record time and date of movement. Fish with PIT tags were detected by transceivers and stationary antennas in the stream. The date and time of detection at an antenna were matched with stream discharge (m³/s) at the same date and time. Most Dolly Varden moved upstream during late summer and early fall. Most cutthroat trout movement was in May, and movement declined through the summer. Few fish moved during the winter. Most fish moved within a narrow discharge range, with a few moving at higher discharges. More than 97% of fish from both species were detected as moving upstream at discharges below the 5% exceedance level during the 4-year period of discharge measurements. Dolly Varden and cutthroat trout moved throughout the entire length of usable habitat in the stream. Connectivity throughout watersheds even within headwater streams is important and can be maintained for these species by use of road crossings that ensure passage over a range of flow conditions such as those described here.