Passive Integrated Transponder Tag Monitoring Reveals Complex Migration and Life History Patterns in Mountain Whitefish in Upper Columbia River Tributaries

Abstract

AbstractMountain Whitefish Prosopium williamsoni is a native salmonid distributed throughout the Columbia River basin, but little is known about the life history traits of tributary‐specific populations. We captured and tagged 129 Mountain Whitefish with passive integrated transponder (PIT) tags between 2010 and 2015 at a weir on the Twisp River, Washington, to assess migration patterns. Detection records suggested that two populations of Mountain Whitefish overlap in the Twisp River during spring: resident fish that spawn in the Twisp River (42% of fish) and migrant fish that spawn in the Okanogan River (58% of fish). The median entry day into the Twisp River was similar for resident (April 17) and migrant (April 16) populations, but median exit day was significantly earlier for migrant (July 2) than for resident fish (November 6). Migrant fish exited the Methow basin and traveled at 14.1 river kilometers per day, passing the lower Okanogan River PIT antenna with a median date of September 17. After spawning and overwintering in the Okanogan River with a median exit date of March 16, these fish returned to the Methow basin traveling at 22.1 river kilometers per day. These results improve our understanding of Mountain Whitefish life history and habitat use in tributaries upstream of Wells Dam, Washington.