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.

Several other headwater areas in the Naches Basin have been hypothesized to be past or current natal areas for bull trout.

The Little Naches River watershed is large and contains apparently suitable bull trout habitat in streams other than Crow Creek and many surveys have been conducted in the Little Naches River and various tributaries over the years (USFS 1996a, Reiss 2008, Kline 2024). There have been individual bull trout sightings reported throughout the Little Naches stream network but their origin is unknown (Anderson 2010). USFS led 3.5 miles of night snorkel surveys in 2007 in the North Fork Little Naches; additional surveys occurred in the South Fork Little Naches in 2008; no bull trout were identified. In 2018 eDNA samples were collected in the middle and north forks of the Little Naches River in an attempt to understand if there was a spawning population. A few samples returned as positive, yet bull trout had still not been physically observed. In 2024 WDFW followed up with a demographic survey in the North Fork Little Naches and more eDNA samples in the north and middle forks. No bull trout were observed over 8 nights of snorkeling and the eDNA sample results were negative for bull trout (Kline 2024). While it is clear that bull trout use portions of the Little Naches watershed as FMO habitat, no signs of successful spawning and rearing have been found outside of Crow Creek.

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 aside from investigations in the upper Little Naches watershed. The Washington Department of Fish and Wildlife Ecological Interactions Team electroshocks sites throughout the Naches watershed to monitor anadromous productivity and occasionally they encounter bull trout.

One juvenile bull trout was documented in Fall Creek, a tributary to the South Fork Cowiche Creek in 2002 during Yakama Nation surveys and WDFW notes indicate an possible report from 1974 (Morris 2002). WDFW followed up with electro-shocking and night snorkeling in 2002 but did not locate additional bull trout or evidence of a spawning population. Cowiche Creek was included in the USFWS Critical Habitat designation based on the Yakama Nation sighting. Since then, no other sightings have been reported, and 3 eDNA samples taken in 2019 did not detect bull trout. Partners in the basin have not typically considered Cowiche Creek an extant bull trout population. Stream temperatures suitable for bull trout spawning and rearing are likely limited to the very upper watershed (Fall Creek and the upper Rock Creek, the South Fork upstream of there, and possibly Upper Reynolds Creek). The Yakima Bull trout Work Group has identified this area as a potential target for future eDNA surveys.

Bull trout have been observed in lower Nile Creek (Todd Newsome, personal comm.), but no spawning and rearing population has been identified. Oak Creek and Little Rattlesnake Creek were surveyed by WDFW and the US Forest Service (USFS 2002). No bull trout were found.