Naches Bull Trout Population Group

Overview

The Naches Population Group consists of three fluvial bull trout populations. Detailed information on each can be found here:

American River Bull Trout Population

Crow Creek Bull Trout Population

Rattlesnake Creek Bull Trout Population

These three populations make use of shared foraging, migration, and overwintering (FMO) habitat in the Naches River, and historically may have mixed with Upper Yakima and Tieton River populations before dams blocked migration corridors in the early 1900s. Naches fluvial bull trout may also utilize the mainstem Yakima river upstream and downstream of the confluence with the Naches River when temperatures are suitable. Information on conditions, threats and actions for this shared FMO habitat are detailed in the Naches River FMO Habitat page.

Population Genetics

The genetic composition of Naches River fluvial Bull Trout populations, including Rattlesnake, Crow, and American/Union/Kettle, reflects gene flow among populations (Small et al. 2009). Most individuals in these populations were assigned to a single genetic cluster with over 90% ancestry, but several individuals displayed mixed ancestry, indicating interpopulation mixing. For example, in the American and Union populations, 8 out of 52 fish had ancestry linked to Rimrock basin fish, suggesting historical spawning events. Crow Creek fish exhibited significant ancestry from Rattlesnake-origin fish, while some Rattlesnake fish had ancestry from American-Union, Crow, SF Tieton, and Indian Creek. Additionally, a few Rattlesnake individuals showed strong ancestry (>94–97%) from SF Tieton and NF Tieton populations, indicating emigration or one-way gene flow due to entrainment (Small et al. 2009).

Population Monitoring

An early 2000s study captured bull trout using hook-and-line as well as weir and box traps (Mizell and Anderson 2010). Sixty-two bull trout were radio-tagged in the Naches drainage. Of the 62 bull trout tagged in the Naches drainage; 29 were captured from various holding pools in the main stem Naches, 16 from the Tieton River below Rimrock Reservoir (Tieton Dam), seven from Rattlesnake Creek, three from the Bumping River, two from the American River and five from Union Creek (American River tributary). The researchers radio tracked bull trout from September 2003 through December 2006. DNA samples were taken and each fish was genetically assigned to a population. The results showed that bull trout move very little during the winter season once they settle into a preferred holding pool (Mizell and Anderson 2010). Summer movements toward spawning areas occurred from May through August, depending on where the spawning tributary was located. Some individuals stayed in the mainstem Naches river throughout the year without migrating to a spawning tributary.

Naches fluvial bull trout spawning is monitored yearly via two to three passes of redd surveys. Other population monitoring has not occurred for these populations.

Note Little Naches potential population area and link to page; cite scott ppt/future report

Note Cowiche controversy- not further addressed as BT populaiton areas