Introductions of non-native and invasive aquatic species are increasing (reviewed in Gozlan et al. 2010) and as a result, so are the prevalence of subject research, management and publications relating to the invasions (Thomaz et al. 2015). Non-native species introductions present significant risk (Gozlan and Newton 2009), often altering the environmental ecology through reduction or elimination of other aquatic organisms in the recipient system (Mack et al. 2000; Gallardo et al. 2015). Non-native fishes are impacting native salmonid populations throughout the Pend Oreille Subbasin, comprised of the Upper Pend Oreille, Priest River, and Lower Pend Oreille subbasins. Non-native fish species currently constitute 64% of the fish assemblage in the Subbasin (KNRD 2017). Competition, hybridization, and predation are primary factors in the decline of native Bull Trout (Salvelinus confluentus), Westslope Cutthroat Trout (Oncorhynchus clarki lewisi; hereafter, WCT), sucker and minnow populations. Therefore, the overarching intent of this project is to implement specific strategies and actions that suppress or eradicate non-native fish in areas where native species are in decline or have been extirpated and recover those populations. Actions conducted through this project have direct impacts on non-native fish species (e.g., reduced abundance, localized extirpation), lead to actions in which non-native fish species are directly impacted (e.g., collect population and distribution data to warrant action; develop management strategies; coordination) or evaluate the post-action response of native fish populations.

Bull Trout and WCT are important native species in the Pend Oreille Subbasin and both have been greatly impacted by non-native fish. Populations of WCT are in decline across their historic distribution (Shepard et al. 1997, 2005). Over 99% of the streams in the Lower Pend Oreille Subbasin, were once occupied by WCT (Shepard et al. 2005), which represented 47% of their distribution in Washington State. In the 622 km of streams surveyed by the Kalispel Tribe Natural Resource Department (Tribe) in the Lower Pend Oreille Subbasin, WCT occupied only 35% of surveyed reaches. Of those, 38% are allopatric WCT populations existing upstream of a natural or anthropogenic passage barrier. Many of the isolated WCT populations persist in small segments and due to population size and limited length of habitat, those populations are at a high risk of extinction from stochastic environmental events and loss of genetic variation (Harig and Fausch 2002; Hilderbrand, 2002, 2003). An estimated 3.4 Km of stream length is required to support a WCT population of 500 age-1 and older fish (Young et al. 2005). Of the 19 isolated allopatric WCT populations evaluated in the Lower Pend Oreille Subbasin, 14 are limited to stream segments less than 3.4 Km (KNRD data).

Bull Trout have declined across their native range and have been listed a threatened species under the US Endangered Species Act since 1999. While many factors have led to the declines (USFWS 2008a), the introduction of (Leary et al. 1993) and impacts by (Donald and Alger 1993; Reiman et al. 2006; Guy et al. 2011; Kovach et al. 2019) non-native species continue to impact Bull Trout. Within the Pend Oreille Subbasin, Bull Trout were historically abundant, with multiple life histories present (e.g., resident, fluvial and adfluvial). Bull Trout populations are now primarily restricted to the Pend Oreille Basin upstream of Albeni Falls Dam, which lacks fish passage, eliminating connectivity to the Lower Pend Oreille Subbasin. Bull Trout observed in the Pend Oreille River and its tributaries below Albeni Falls Dam are now rare. Bull Trout in the Upper Pend Oreille Subbasin—those utilizing Lake Pend Oreille and its tributaries, are presently stable, yet continue to face threats of hybridization, predation, and competition by non-native fishes. Within the Priest River Subbasin, Bull Trout were abundant and provided a harvest-oriented trophy fishery in Priest and Upper Priest lakes (Bjornn 1957; Mauser et al. 1988). However, harvest opportunities were discontinued in 1984 following significant declines. Although the harvest was removed, a positive population response did not occur (Mauser et al. 1988), as non-native species continued to impair the remaining population.

In tributaries, Brook Trout (Salvelinus fontinalis) are the most ubiquitous and problematic for native salmonids in the Pend Oreille Basin.  Due to their spawn timing and earlier emergence, young of year Brook Trout (Griffith, Jr. 1972) are notably larger than their WCT counterparts which leads to a competitive advantage and displacement of WCT in areas of overlap (Abbott et al. 1985; Behnke 1992; Wootton 1998). To prevent further declines to native salmonids, the Tribe and partners have implemented actions to reduce the abundance of non-native fish. When geographic isolation occurs (e.g., waterfall, culvert, fish management structure), mechanical, chemical, or alternative methods can be applied to remove non-native fish, allowing natural or assisted re-occupancy of the vacated habitat. Through the history of this project, a several methods have been employed to protect and restore native WCT populations; piscicides were applied, fish management structures installed, and mechanical suppression was and continues to be conducted.  

Saucon Creek, a tributary to West Branch LeClerc Creek, is a priority watershed under the Pend Oreille PUD Settlement Agreement (US-FERC 2008). Isolated by a natural barrier near its confluence, Saucon Creek has a sympatric population of Brook Trout and WCT in the lower 2.1 km, above which exists a an allopatric WCT population. Multiple-pass electrofishing treatments to remove Brook Trout have been used since 2014 and is currently approaching complete eradication of Brook Trout.

Mill Creek and its tributaries encompasses 30.6 km above a natural barrier. Mill Creek has a sympatric population of Brook Trout and WCT, with several small, isolated headwater segments of allopatric WCT. This project was initiated in two phases, with the first (upper project area) starting in 2018, and the second (lower project area) in 2019. This mechanical suppression treatment is unique as it is markedly larger in size than other treatments conducted through this project, although the same electrofishing techniques are applied.  This project coupled with past successes, lends confidence that expanding efforts to larger watersheds can expedite the reduction of non-native salmonids in tributaries, preserving remaining populations of native salmonids. Coupling current suppression efforts with advancements in technologies and methods, should increase the size, shorten duration, and decrease cost of conservation outcomes in the subbasin.

One such advancement is the use of Myy (Trojan-Y chromosome) Brook Trout. The Washington Department of Fish and Wildlife (WDFW) and Tribe recently partnered with Idaho Fish and Game (IDFG) and the Western Association of Fish and Wildlife Agencies (WAFWA), to conduct pilot studies that evaluate the application of stocked Myy Brook Trout (Schill et al. 2016) in projects actively suppressing Brook Trout. This technique is intended to expedite the removal of the Brook Trout population, as Myy Brook Trout produce only male offspring, which over time will skew the population sex ratio toward predominantly males (Schill et al. 2017). The theoretical result is eventual elimination of females and extirpation of the population (Schill et al. 2017; Kennedy et al. 2018). Mill Creek was selected by WDFW as a candidate to conduct an Myy Brook Trout pilot study. To determine if stocked Myy Brook Trout are influencing the extant population, an annual genetic evaluation of juvenile Brook Trout will occur. Parentage analysis (Wang 2004, 2014) of juvenile Brook Trout reveals if and to what extent Myy’s are contributing to wild stocks. Progeny sex ratio will signal if the population is being biased toward males over time (Schill et al. 2017; Kennedy et al. 2018). As WDFW is responsible for stocking Myy Brook Trout, this project will contribute through data sharing and financial assistance with genetic/parentage analysis. The application of this  management action is novel and as such is being evaluated over multiple geographic areas in the western US (i.e., WAFWA organization). The development and refinement of this technology hinges on project such as Mill Creek. If successful, the application of sex ratio augmentation through combined Myy stocking and active suppression of the wild population, could greatly enhance the ability to preserve and expand tributary native fish populations, reduce cost and public concern, and perhaps be applied to different species or larger systems.

Lake Trout (Salvelinus namaycush) in Priest Lake had been robust for decades, yet Lake Trout were not abundant in Upper Priest Lake until the late 1990’s (Fredericks 1999). Connected through the Thorofare, Lake Trout occupied Upper Priest Lake through migration from Priest Lake. By 1998, Lake Trout abundance in Upper Priest Lake was estimated to be 859 fish (Fredericks 1999). Due to decades of impacts, particularly those imposed by Lake Trout, Upper Priest Lake Bull Trout are considered depressed, while those in Priest Lake are considered functionally lost (DuPont et al. 2007). With concerns for native fish populations, a Lake Trout removal program (i.e., gill netting) was initiated in Upper Priest Lake in 1998. With a promising response in the Upper Priest Bull Trout population, the 2019-2024 IDFG Fisheries Management Plan renewed the native fish conservation goal, setting the stage for continued Lake Trout reduction efforts (IDFG 2019). This project cost shares suppression efforts in Upper Priest Lake, with the intent to stabilize Bull Trout and other native fish populations.

Northern Pike (Esox lucius; hereafter, pike) were an unwelcomed and potentially disastrous addition to the Pend Oreille Subbasin.  Pike are a large apex predator with a Holarctic distribution (Scott and Crossman 1973), naturally occurring in North America from portions of Alaska south to Missouri and Nebraska east of the Rocky Mountains and west of the Appalachian Mountains, but historically absent in Pacific drainages south of Alaska. Pike have been introduced outside of their native range in the northwestern contiguous United States (Fuller and Neilson 2019), southern British Columbia, Canada (Baxter and Doutaz 2017) and Alaska (ADFG 2007).  Illegal introductions (1950’s-1990’s) established populations in the Blackfoot, Clark Fork, and Flathead rivers in Montana (Huston 1985; Berg 2003; summarized in Bernall and Moran 2005), which form the headwaters of the Pend Oreille Basin. No pike were collected in electrofishing, gill netting, and beach seining surveys conducted in Box Canyon Reservoir from 1987 to 1992, when 92,967 fish were examined (Barber et al. 1989; Bennet and Liter 1991; Ashe and Scholz 1992). No pike were detected in any Box Canyon Reservoir in subsequent surveys until 2004.

Pike are opportunistic piscivores that prey on fish within weeks of hatching (Ratt 1988). Pike have eliminated fish species (He and Kitchell 1990) and in certain instances, the entire prey base (Nicholson et al. 2015). Pike demonstrate opportunistic feeding strategies that reflect species availability (Margenau et al 1998). During their expansion Box Canyon Reservoir (i.e., 2004-2011), the catch per unit effort (CPUE) of pike increased more than five-fold in reservoir surveys, while declining significantly for most other species (Meyer and Garrett in prep). Though salmonids were a small percentage of the pike diet in Box Canyon Reservoir (Bean et al. 2011; Harvey 2011), Muhlfeld et al (2008) estimated that the population of 1,200 to 1,300 pike in the Flathead River consumed more than 13,000 WCT and nearly 3,500 Bull Trout. Due to rapid growth potential, large ultimate size, and plasticity in the diet of pike, most life stages of resident and migratory fish in the Pend Oreille River and downstream waters, including the anadromous portion of the Columbia River, are potential prey. The Independent Scientific Advisory Board conducted a review of predation impacts and management effectiveness in the Columbia River Basin (ISAB 2019), where they described several conclusion relating to pike entering the anadromous zone. In general, where no refuge exists, pike can drive preferred prey toward extinction, and all but adult salmon can be consumed, with pre-smolt life stages the most vulnerable as they likely co-occupy preferred habitat. Efforts to increase the relative abundance of native salmonids in the lower Pend Oreille Subbasin through mainstem fish passage projects, tributary restoration, and conservation aquaculture may be seriously compromised by the continued (allowed) expansion of pike. Moreover, uninterrupted spread through emigration and illegal transport within the Columbia Basin poses serious ecological risk, particularly for ESA listed salmon and steelhead stocks.

The Tribe and WDFW developed a joint management position to: (1) minimize the impact of pike to native fish species, (2) reduce the number of pike in Box Canyon Reservoir, and (3) reduce the spread of pike downstream while preventing further illegal introductions. Pike were designated a prohibited species in Washington State in 2011, with harvest promoted through fisheries contests and liberalized regulations. Following a successful pilot study in 2011 (see 2012 proposal), and projects demonstrating similar success (summarized in Dunker et al. 2018; 2012 proposal), we hypothesized that a spring netting strategy targeting staging and spawning pike could be scaled up and applied to Box Canyon Reservoir, resulting in their considerable reduction. Therefore, the initial (2012) project objectives were to reduce the relative abundance (i.e., CPUE) of pike >350 mm total length in Box Canyon Reservoir, as evaluated in an annual Spring Pike Index Netting (SPIN) survey (see BPA project No. 199700400), from 13.2 to <1.7 pike/net-night in the southern half of Box Canyon Reservoir and from 2.9 to <0.5 pike/net-night in the northern half of Box Canyon Reservoir. Meeting initial objectives (Bean 2015), the current focus is limiting their relative abundance at or below the initial targets, preventing reestablishment, and limiting entrainment. The current suppression strategy remains consistent, and is only modified in terms of total effort applied annually, which is reflective of recent data and surveys.

In 2016, Pike were detected and evaluated (i.e., SPIN survey) in Boundary Reservoir, and their relative abundance was higher than anticipated (Harvey and Bean 2016). As this reservoir has significantly less available habitat (i.e., limited to upstream one-third), and is frequently subjected to fluctuations in elevation (i.e., Boundary Dam operations) which likely limits recruitment, a markedly reduced effort would be necessary to suppress the pike population. The objective for Boundary Reservoir, established to model Box Canyon Reservoir, is to reduce pike to less than 0.5 pike/net-night in annual SPIN surveys. This objective was established to ensure pike are limited (i.e., reduced) to the point that downstream entrainment events were minimized.

Literature Cited: see attached 2020 Project Proposal (https://www.cbfish.org/Document.mvc/Viewer/P181279)