South Fork Tieton Bull Trout Population

Overview

The South Fork Tieton River is the largest tributary of Rimrock Lake, entering the reservoir from the south at its eastern end. Prior to impoundment the South Fork joined the North Fork in McAllister Meadows to form the mainstem Tieton River. The South Fork Tieton River originates in the Goat Rocks Wilderness Area, and most of the stream is contained within the Okanogan-Wenatchee National Forest. A waterfall 14.2 miles upstream of the reservoir represents an impassable barrier for migratory fish. Numerous small tributary streams enter the South Fork Tieton River below this waterfall, including Bear, Short and Dirty, Grey, Spruce, and Corral creeks. Bear Creek, which enters the stream 1.6 mile below the barrier falls, is the largest of these.

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Population Information

Population Distribution and Life History

The South Fork Tieton River supports a single local population of bull trout, which displays an adfluvial life history type. It is possible that a resident component exists as well although this has not been confirmed. The known spawning area for this population is located entirely within the National Forest, extending from about RM 5.0 to the waterfall (Figure 13). It also includes Bear Creek but none of the other tributaries. What about the lower portion of Spruce and Camp Creeks?

Figure 13. South Fork Tieton River subwatershed

Juvenile bull trout primarily rear within the spawning area and have also been found in several of the creeks in which spawning activity has not been documented. Rimrock Lake provides FMO habitat for subadult and adult fish. It appears that adult bull trout enter the South Fork Tieton River prior to spawning earlier than other populations in the Yakima Basin. A copy of a local angler’s fishing journal provided to Eric Anderson documented his catch from 1987-1994 and included bull trout caught in June. Snorkel surveys in 2000 to document spawning migration timing found adult bull trout moving into the river in late July (James 2002a).

Natural Barriers limiting distribution

A 30 foot waterfall near RM 14, South Fork Falls, is an impassable barrier to migrating adfluvial Bull Trout. Barrier falls also occur on Bear Creek (near RM 0.75).

Population Genetics

Results of genetic analyses show that this population is genetically distinct from all other populations in the Yakima Basin including the other adfluvial populations residing in Rimrock Lake to which it is physically connected (Indian Creek and North Fork Tieton River). The population did cluster with the other Naches River fluvial populations, indicating some degree of gene flow (Reiss 2003; Small et al. 2009). This likely reflects a pre-dam exchange of genetic material or a more recent one-way genetic contribution from entrained fish. All genetic samples were collected from post-spawn adults captured in 1996 and 2000 in a box trap deployed in the river. Connectivity and thus the potential for genetic exchange with downstream populations in the Naches River fluvial system was eliminated by the construction of Tieton Dam in 1925.

Population Monitoring

WDFW began exploratory spawning surveys in the South Fork Tieton River in 1990 with a mainstem index area established and complete surveys started in 1994. Bear Creek was included in the survey after WDFW found numerous bull trout in the lower end of Bear Creek during electroshocking surveys that same year. Short and Dirty Creek was also electrofished in 1994, and juvenile bull trout were observed (Anderson 1994). In 1993 the Forest Service captured juvenile bull trout in minnow traps in several South Fork Tieton tributaries (Milk, Bear, Spruce and Corral creeks) (USFS 1993b). Sexauer (1994) estimated juvenile bull trout population density and derived length frequencies for both juveniles and adults in the South Fork Tieton River in 1992. The author also studied life history aspects of the species in the river and documented habitat use. James (2002a) trapped and tagged bull trout annually from 1995-2000 and conducted snorkel surveys in 1992, 1996, and 2000 while studying the population status and life history characteristics of the South Fork Tieton population. WDFW snorkeled and electroshocked Bear Creek in 2003 as part of a project to develop a bull trout presence/absence sampling protocol (Hoffman et al. 2005). Larsen et al. (2003) examined these data in more detail, and Peterson et al. (2005) provided final analysis.

The results of studies investigating the entrainment of Rimrock Lake bull trout through the outlet works of Tieton Dam were discussed previously in the Population Monitoring section for Indian Creek. Also discussed was the collection of 37 bull trout from the stilling basin directly below Tieton Dam during a fish salvage effort in 2005 and the subsequent analysis of genetic samples taken from these fish. This analysis revealed that eight of the bull trout captured in the stilling basin below the dam assigned to the South Fork Tieton River population (Small et al. 2009).

In 2022 and 2023 WDFW performed night snorkel demographic surveys covering XX RM, only accounting for XX % of available habitat. Adult, juvenile, and YOY Bull Trout were observed.

Other Distribution Data (eDNA, etc.) ? or include in narrative above?

-WDFW demographic data 2022-2023?

-USFWS Trap and Haul data

-any info from above falls?

Redd Survey Data

Figure 12.

The spawning period for the South Fork Tieton River population occurs primarily during the month of September but can extend through mid-October. Complete bull trout redd surveys have been conducted in an index area on the South Fork Tieton River since 1994. This index area begins at river mile 8.4 in an area locally referred to as “Blue Slide” and extends 5.8 miles upstream to the barrier waterfall. Also included in the annual survey is 0.6 mile of Bear Creek from the mouth to an impassable barrier. This creek annually hosts large numbers of spawners despite its relatively small size and limited accessible length. Many years, especially over the last decade, additional surveying has been done in a 3.5-mile reach directly below the mainstem index area with as many as 30 additional redds found. Despite these observations there are currently no plans to expand the South Fork Tieton River index area to include this reach. To do so would make population trend comparisons across all years difficult. The redd counts presented below in Figure 12 do not include redds observed in this additional reach. Confirm with Marc?

Excluding 1995 (an incomplete survey year), an average of 187 redds has been counted annually. The highest counts during the period of record have been observed in three of the last four years (surveys were hampered in 2010 by high flows).

Population Status and Trend

The USFWS (1998) did not consider the South Fork Tieton River population singularly. The agency considered the Rimrock “subpopulation” to be stable and increasing. WDFW similarly lumps the Rimrock adfluvial populations and rates the status of this stock as healthy (WDFW 2004).

The South Fork Tieton River population has been the most stable bull trout population over time in the Yakima Basin and is currently considered the strongest in terms of abundance. Despite some years with average and above average redd counts the population appears to be trending downward since the original Yakima Bull Trout Action plan was published in 2012. 88 redds were counted in 2024, the lowest number since complete surveys began in 1996.

(Insert graph of redd counts; ideally via live link)

Habitat

Habitat Overview

South Fork Tieton River elevations range from 2,900 feet at the mouth to 3,850 feet at the base of the impassable waterfall located just over 14 miles upstream. As mentioned previously this entire reach is located in the Okanogan-Wenatchee National Forest. The primary land use activities in the watershed are recreation and livestock grazing. Bank erosion and riparian damage has occurred in areas where two established campgrounds and scattered dispersed campsites are located. These same impacts have resulted from off-road vehicle use near the stream. The Forest Service has actively addressed these issues over the last decade. Livestock grazing (and direct access to the river) has also impacted bank stability and riparian condition, most likely to a greater extent than recreation, as it has been more widespread. While significant measures have been recently implemented to address grazing impacts, they are an ongoing issue. Timber harvest has been heavy in the past but is now limited. However, the associated roads remain and road density in the watershed is relatively high. Except at crossings these roads are generally not close to the river, but a relatively high percentage of them (30%) are within high erosion hazard landforms (Haring 2001). Forest health in the South Fork Tieton watershed is a definite concern. A growing fear is that extensive beetle kill combined with high tree density could fuel a catastrophic wildfire.

Despite the impacts described above spawning and rearing habitat conditions in the South Fork Tieton River are considered very good. Channel and riparian condition, LWD, pool frequency and quality, and water temperatures all rate high (Haring 2001). The river appears to receive considerable sediment input from various sources, particularly in the area known as “Blue Slide” (RM 8.4), which is a natural landform. One potential concern derives from hydraulic conditions at the mouth of the river.

The issue is one of habitat access and was created when a bridge on Forest Service Road 1200 was constructed years ago. The natural channel of the river was relocated to flow under the bridge through a notch blasted out of bedrock. A waterfall begins to form at this location when the reservoir is drafted below 131,000 acre-feet. It is believed to become impassable for bull trout attempting to migrate upstream when the pool volume drops below 127,000 acre-feet (Thomas 2001). An informal agreement is in place with the USBR to maintain at least this minimum pool through August 10 of each year, the date Yakima basin biologists agree bull trout have likely concluded their spawning migration into the South Fork Tieton River. Under current operations heavy drafting of Rimrock Lake does not begin until early September and the reservoir has held more than 127,000 acre-feet on August 10 (average 177,155) for the 32 years since modern-day operations (i.e., flip-flop) were initiated in 1981. Previous to this at least part of the spawning migration may have been blocked from entering the South Fork Tieton; should a proposal to change current reservoir operations occur in the future it could resurface as an issue.

Take note of current bridge replacement and re-route of SFT project

Extent of available spawning and rearing habitat

Check above under overview of population distribution and life history? Pull down description or remove this sub heading

Habitat Monitoring

Sexauer (1994) surveyed habitat use by juvenile and pre-spawning adult bull trout. Thomas (2001) assessed the potential impact of the waterfall at the confluence with Rimrock Lake on bull trout passage. Two glaciers, Mead and Conrad, are in the headwaters of South Fork Tieton River. USGS (Josberger et al. 2007) have photographic evidence and density measurement showing that Conrad Glacier is receding. Flows may decrease as these glaciers recede.

Mongillo (1982) measured water quality parameters and zooplankton densities for Rimrock Lake.

The Forest Service and the Yakama Nation Timber Fish & Wildlife Program (TFW) have worked cooperatively to maintain a long-term data set of sediment monitoring data in the South Fork Tieton River (Matthews 2011). There are three reaches that have been sampled every year from 1999 to present. Is this still ongoing? This monitoring effort demonstrates an overall relatively high level of fine sediments in the substrate within the spawning reach (~12-14%), which would qualify as “functioning at risk” (USFWS 1999) and may indicate a need to address sediment sources in the drainage.

Field Habitat Surveys

The Forest Service completed habitat surveys on the South Fork Tieton River in 1991 (15.8 miles) and again in 2000 (6.0 miles) using Hankin and Reeves protocol (USFS 2003c). Yakama Nation was working on another habitat survey in 2024.. Check with Jonny Lambert YN. Bear Creek and other associated tributaries were surveyed between 1991-1998. In all of these surveys, data were collected on pool/riffle frequency, riparian and channel condition, substrate, LWD, and temperature.

Stream Temperature Data

The South Fork Tieton River was monitored for temperature via thermographs deployed at three sites on the mainstem during the summer low flow period in the majority of years from 1995-2007 (USFS 2011a). Other thermographs were deployed in associated tributaries, including Bear Creek during that same time period, primarily in 1995. There was a monitoring gap in temperature data from 2007 - 20XX when the USFWS deployed loggers in the lower mainstem. In 2023 USFS monitored temperatures in Grey Creek and Spruce Creek, tributaries to South Fork Tieton. In 2024 Mid-Columbia Fisheries deployed temperature loggers in all the Bull Trout spawning indexes.

Other Habitat Data/Monitoring

Anything to put here? Keep this sub-heading?

Threats

Tied to stuff from SSA

Similar to the Indian Creek population, several of the highest severity threats to the South Fork Tieton population result from the presence of Tieton Dam are (passage barriers, entrainment, and prey base). The dam precludes upstream gene flow from Naches River fluvial populations, entrains adult and subadult fish through the outlet works, and has eliminated anadromous fish access to the South Fork Tieton River. Other high and medium severity threats include illegal angling in Rimrock Lake, potential introgression with brook trout, recreation activities (campsites adjacent to spawning areas), extensive forest health issues (forest management), and grazing. There is a grazing allotment within the spawning and rearing area but an agreement stipulates that cattle are to be excluded during the spawning period. < --- Is this still accurate?? However, cows were observed in Bear Creek in 2011 during spawning, which may constitute a significant threat. Agriculture, altered flows, development, dewatering, limited extent of habitat, transportation, and mining are not threats present for this population.

Connectivity

Fish Passage Barriers (Check/update FDSI)

Significant

Entrainment (Dams? Irrigation Diversions?)

Unknown Significant

Water Quantity and Quality

Current and modeled future temperature conditions

(iFrame of NORWEST results?)

Summary of Primary Limiting Factors

(Look at threat summary table format and Teanaway example)

Recovery Strategy

Population-level Recovery Strategy

(High-level discussion of priority needs)

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Actions

Completed Bull Trout Recovery Actions

(Mix of narrative and table, or could be a database)

Recommended Actions

(Link to or summarize BTAP database)