PROJECT BACKGROUND

Non-native fish species are impacting native salmonid populations throughout the Pend Oreille Subbasin. Competition, hybridization, and predation by non-native fish have been identified as primary factors in the decline of native Bull Trout (BT) and Westslope Cutthroat Trout (WCT) populations. The majority of tributaries to the Pend Oreille River were historically occupied by native WCT; now less than 35% harbor WCT. Although anthropogenic impacts contributed to significant declines over the past century, corrections to those impacts (i.e., habitat modifications), in the presence of non-native fish tend to benefit invasive species instead of native species. Therefore, the goal of this project is to implement actions to suppress and/or eradicate non-native fish in areas where native populations are declining or have been extirpated and reintroduce native fish species where appropriate. These projects have been identified as critical to recovering native ESA-listed BT and declining populations of WCT. Actions developed through this project have either direct impacts on non-native fish species (e.g., reduced numbers through suppression/eradication activities),  lead to actions in which non-native fish species are directly impacted (e.g., collect fish distribution data to warrant action; develop management strategies for non-native fish species; collect data on impacted native salmonid populations) or monitor the response to recovered native fish populations  following actions taken against non-native fish species. As such this project will discuss the following actions:

1. Mechanical Suppression: Physical removal of non-native fish species of interest by way of electrofishing, netting (gill, fyke, seine, etc.), trapping (weir, light-minnow, minnow, etc.) or angling leading to a reduced, depressed or potentially eliminated population.

MECHANICAL SUPPRESSION AND MONITORING ACTIVITIES IN TRIBUTARIES

MILL CREEK (MILL SUBBASIN): Mill Creek historically contained a pure WCT population but now is comprised largely of EBT, although a genetically pure, low density WCT population remains. Resident (non-migratory) fish in Mill Creek are protected from further invasion of EBT by a natural migratory barrier low in the creek, within approximately one mile of its confluence with the Pend Oreille River; this barrier is likely passable by large migratory salmonids at least seasonally. In 2018, mechanical suppression of EBT using multiple-pass depletion electrofishing techniques was initiated. Due to the size of the project area (barrier to headwaters), the project was separated into two sections. The upper (headwaters) section begins above the confluence of Mill Creek and Sylvis Creek (13.6 km).This sections received a suppression treatment in 2018 and 2019. The lower section includes the remainder of Mill Creek and tributaries from just below Sylvis Creek to the barrier (17 km); the first suppression treatment occurred in 2019. In total, nearly 15,000 age-1 and older EBT have been removed from mill Creek since 2018. Suppression will occur throughout the entire 30.6 km project area in 2020. Juvenile EBT genetic samples will be taken to monitor the contribution of Myy Brook Trout (stocked by WDFW) toward shifting the population to predominantly males, thereby expediting the eradication of Mill Creek Brook Trout.

SAUCON CREEK (LECLERC SUBBASIN): Saucon Creek historically contained a pure WCT population and is now comprised of a mixed population of EBT and WCT. Saucon Creek is protected from further invasion of EBT by a barrier low in the creek near the confluence with West Branch LeClerc Creek. Mechanical suppression of EBT using electrofishing techniques began in 2014 in the 2.1 km section where sympatric populations of WCT and EBT exist; upstream of this point is occupied by allopatric WCT. In total we have removed >3,300 age-1 and older EBT in Saucon Creek (2014-2019) and project trends indicate EBT densities are decreasing annually, with WCT densities increasing. In 2020, we will conduct an additional EBT removal treatment and anticipate similar project trends.

MECHANICAL SUPPRESSION AND MONITORING ACTIVITIES IN MAINSTEM RIVERS OR LAKES

PEND OREILLE RIVER NORTHERN PIKE SUPPRESSION: Northern Pike (NP), illegally introduced in the Clark Fork River, Montana has immigrated to the Washington’s Pend Oreille River, where they have caused drastic declines in native species and gamefish being managed by State and Tribal agencies. Northern Pike threaten to undermine current and future recovery efforts for BT and WCT, as well as other native salmonids, minnows, suckers and introduced gamefish in the watershed. Northern Pike also pose significant risks to the anadromous fisheries of the Columbia River and Endangered Species Act (ESA) recovery efforts if left unchecked to emigrate further downstream.

After engaging the public in 2011-2012, KNRD and WDFW developed a 3-pronged approach to suppressing the Pend Oreille River Box Canyon Reservoir population to pre-2004 levels: increasing angler harvest through outreach and education, targeted (harvest-oriented) fishing contests, and mechanical suppression of the population with gillnets. The objective was initially to reduce the abundance of NP in Box Canyon Reservoir from the 2011 Spring Pike Index Netting (SPIN) survey catch-per-unit-effort (CPUE) value of 13.2 NP/net night in the southern half (core area from Pioneer Park to Riverbend including sloughs) to <1.73 NP/net night and from 1.9 NP/net night in the northern half (Riverbend to Box Canyon) to <0.5 NP/net night.

KNRD, with support from WDFW has implemented eight years of mechanical suppression in BCR (2012-2019) with project support provided by BPA, US Bureau of Indian Affairs, WDFW, Kalispel Tribe, and Avista Corporation. Up to 35 specifically designed gillnets gill nets were deployed and retrieved daily, with target net saturation generally occurring from ice-off (March) through the spring freshet (June) or ended earlier if target reduction was met (2014) or later phases were unplanned (2015-on).

Thus far nearly 18,000 NP have been removed in 5,200 overnight gillnet sets in the BCR. Based on 2019 SPIN results, the adult population in the core area (southern half of BCR and sloughs) was reduced by >90% from the 2011 baseline of 13.2 NP/net to 0.36 NP/net night. Although the BCR population is largely depressed, the 2019 project and monitoring results showed a slight increase in total catch, although it was generally localized.

Recreational angler harvest appeared negligible based on observations by field staff, derby results, and anecdotal reports and as anticipated, mechanical suppression removed the vast majority of NP. In 2015, a report on the effectiveness of mechanical suppression to remove 87% of the NP population was produced as a supplemental technical report to the 2015 Non-Native Fish Suppression (BPA Project No. 2007-149-00) annual report and submitted the Independent Scientific Review Panel of BPA’s Fish and Wildlife Program and is available to interested parties.

A 2016 SPIN survey in the downstream Boundary Reservoir indicated the NP relative abundance was higher than anticipated and warrants additional mechanical suppression. In the first year of monitoring the downstream Boundary Reservoir, the CPUE for sloughs was 5.44 NP/net night and 1.58 NP/net night in river sets, indicating suppression efforts needed to expand downstream to the upper section of this reservoir. Suppression efforts thus far (2016-2019) have removed 590 Northern Pike in 396 gillnets. CPUE in SPIN surveys has annually declined and was 0.23 and 0.10 NP/net in the slough sets and river sets, respectively. This indicates the population had been reduced significantly from 2016, and is below the relative abundance target for the reservoir of <0.5 NP/net night.

Suppression will continue in 2020 for both reservoirs. Based on the 2020 Northern Pike suppression (March-April) and SPIN Survey (May) results for Box and Boundary reservoirs, the necessity and level of suppression will be developed for 2021. Staff from the Tribe and WDFW will meet annually and use all available data and information to make the appropriate decision on out-year suppression activities in both reservoirs.

LAKE TROUT SUPPRESSION IN UPPER PRIEST LAKE (IDAHO): The Idaho Department of Fish and Game (IDFG) has been suppressing Lake Trout in Upper Priest Lake (UPL) through extensive gill netting since 1997.  A larger effort has been annually implemented since 2007, with >30,000 Lake Trout (LKT) removed since 2007. Bull Trout redds are monitored in the UPL watershed and have increased from 7 (2007) to 91 (2017), with the most recent (2019) count at 67 redds.

The Hickey Brothers Research (LLC) will again be contracted to use gillnets to remove LKT from UPL. Gillnets will be fished over a 7 day period in late May/June 2020. Nets will be oriented based on catch rates at a particular site and on the discretion of the netting crew; effort will be made to avoid incidental BT captures. Data from the 2020 effort will be summarized and compared to previous efforts to monitor project effectiveness and success. This project provides cost-share funding to continue LKT suppression. The US Fish and Wildlife Service also contributes significant project funding. Continuing to reduce LKT predation and competition with BT and WCT through reduction and/or eradication efforts will assist in BT recovery and long term persistence of all native fish in UPL.

INVASIVE SPECIES DETECTION AND MONITORING

Environmental DNA (eDNA) sampling technology greatly improved our ability to detect invasive fish species and understand their distribution. As we move forward with non-native fish management and prevention, we will continue to apply such proven and novel techniques as appropriate. In 2020, we will continue to use eDNA sampling as suppression and eradication projects in tributaries and larger bodies of water are investigated, developed, implemented, or monitored.

INVASIVE SPECIES COORDINATION AND PROJECT RESULTS SHARING

Given the scope of this project and the nearly two decades of invasive species management by KNRD, it is becoming more critical to be involved with the coordination of invasive species issues and information sharing. In 2020 KNRD, through this BPA project and other programs, will continue to  attend and present invasive species management data at local and regional venues. This project will also support staff attendance at local and regional coordination and technical staff meetings focused on addressing invasive species. The focal area is the Columbia River Watershed but other opportunities to address broader invasive species issues will be considered and attended as appropriate.