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The overall objective of this pilot project is to determine whether mechanical modification of dense beds of EWM can improve fisheries habitat in Noxon Reservoir. We propose to reduce the amount of invasive watermilfoil in two plots in the reservoir and create boater lanes using a mechanical harvester, and monitor the results to see if the mechanical manipulation of the dense weed beds creates more edge habitat for the reservoir fishery and improves the angling experience. The results of this pilot project will help drive future management decisions in the Noxon and Cabinet Gorge reservoirs.

This project is intended to address the lack of quality littoral habitat structure in the reservoirs. The reservoirs are infested with EWM, which creates a monoculture habitat both along shorelines and in interior beds. By altering these beds, we hope to improve that habitat for the Smallmouth and Largemouth Bass sport fishery. These actions are consistent with Montana Fish, Wildlife and Park’s (MFWP) fishery management goals for Noxon and Cabinet Gorge reservoirs (https://fwp.mt.gov/binaries/content/assets/fwp/fish/statewide-fisheries-management-plan/2019-2027-sfmpg.pdf) as well as with the purpose and goal of the Montana Tributary Habitat Acquisition and Recreational Fishery Enhancement Program under the Clark Fork Settlement Agreement (https://www.myavista.com/about-us/celebrate-our-rivers/federal-licensing), which has funded much of the EWM treatment to this point.

This pilot project also is consistent with the Sanders County AIS Management Plan (https://sanderscountyais.com/management), which calls for the adaptive management of aquatic invasive plants in the reservoirs and the goals of Montana’s Statewide Strategic Framework by addressing the objective to “ensure that invasive species control restores the desired ecological, economic, and cultural values to the land that is being managed,” and allowing for adaptive management to learn from past experiences, improve effectiveness and reduce impacts. (http://dnrc.mt.gov/divisions/cardd/docs/misac-docs/misac-resources-docs/2016-montana-invasive-species-strategic-framework.pdf/)

Background:
Noxon Rapids Reservoir was created by the Noxon Rapids Dam, which was completed in 1959 and is operated by Avista Utilities. The reservoir is on the Clark Fork River in Sanders County near the city of Trout Creek, Montana. The 35.5-mile long reservoir is 2.5 miles wide and bound upstream by the base of Thompson Falls Dam, which is owned and operated by NorthWestern Energy. At full pool, Noxon Rapids Reservoir is 7,852-surface acres with an average depth of 65 feet and a maximum depth of 200 feet.

Natural resource needs in the Noxon and downstream Cabinet Gorge reservoirs are addressed under the 1999 Clark Fork Settlement Agreement, a 45-year agreement developed by 26 stakeholders in the basin. Among the priorities of management are to enhance the recreational fishery. One of the most popular recreation activities in the reservoirs is fishing of Smallmouth and Largemouth Bass, Northern Pike and Yellow Perch. The elimination of large water level fluctuations by Avista in the 1980s resulted in successful reproduction of bass species, which has resulted in increased angling pressure. In 2015, 26,000 angler days were recorded on Noxon Reservoir, ranking it third in MFWP’s Region 1 for angling pressure.

Noxon Reservoir hosts up to seven bass fishing tournaments annually and currently holds the state record for largemouth bass. A 2015 creel survey found that most anglers targeted either species of Bass, followed by Northern Pike and Yellow Perch. Between April and November, 1,324 were people interviewed on Noxon Reservoir, and 30 to 40 percent were targeting either Smallmouth or Largemouth Bass or both. Survey participants caught 11,500 fish of 15 different species.

Fishing is one of Montana’s biggest outdoor industries, reeling $919.3 million into the state in 2017, according to the 2020-2024 Statewide Comprehensive Outdoor Recreation Plan. Montana’s fishery draws many people to the state and nonresident travel is a big income generator in Sanders County. In 2019, the estimate of non-resident traveler spending in Sanders County was $20.3 million, according to Institute for Tourism and Recreation Research at University of Montana. But Montanans are avid anglers as well – of those participating in the Noxon Reservoir creel survey in 2015, 85 percent were Montana residents.

Eurasian watermilfoil was first confirmed in Noxon Reservoir in 2007. In 2008, the Sanders County Commissioners established the Sanders County Aquatic Invasive Plants Task Force (Task Force) to develop and implement an integrated weed management approach to contain and manage infestations of EWM. In May 2010, an environmental assessment was prepared that covered herbicide treatment of EWM, Curly Leaf Pondweed, and Flowering Rush in Noxon and Cabinet Gorge reservoirs. This environmental assessment was subsequently approved in July 2010. Widespread herbicide treatment of EWM in Noxon Reservoir occurred from 2012 to 2016 and primarily focused on large dense beds of EWM throughout the reservoir. In 2017 no treatment occurred while the Task Force conducted an alternatives analysis for treatment of EWM in the reservoirs. Based on this analysis and input from stakeholders, treatment of EWM shifted from reservoir-wide to treatment of priority areas near public and private access sites, including public and private boating access sites and shoreline dock areas, and when funding is available, high density shallow access areas with significant boat traffic. Priority treatment areas within the proposed action area are determined annually based on pretreatment sampling results and available funding.

In recognition of this shift and the low probability that EWM will be extirpated from either Noxon or Cabinet Gorge reservoirs, there is interest in managing this invasive plant to benefit the reservoirs’ fishes and fisheries. Modifying EWM beds to benefit the fisheries is consistent with the findings of a literature review of EWM conducted by Avista to gain insight into the potential effects of EWM on fishes in Noxon Reservoir. (Kusnierz, 2021)

We plan to test the efficacy and desirability of mechanically harvesting EWM with the intention of improving fish habitat during the summer of 2022. This pilot project will see if mechanical harvest is an effective tool to address the reservoirs’ lack of quality littoral structure. Currently, the reservoirs are annually infested with large dense beds of EWM, with the acreage ranging year to year depending on conditions. The effects of EWM are wide-ranging and include those that can affect water quality, fish communities, and recreation access.

When EWM is dominant it can alter phosphorous levels in the water column, reduce chlorophyll concentrations, alter temperature, and reduce dissolved oxygen concentrations as compared to open water habitats and areas containing native macrophytes. Water quality monitoring does not show an excess of nutrients in the Noxon Reservoir, however, but potential reductions in dissolved oxygen concentration may be a concern, as it can inhibit reproductive success of fish.

Macrophyte species and density can affect macroinvertebrate demographics and dense stands of macrophytes can have varied impacts on fish species depending on the species’ habitat preferences, feeding habits, and predatory fish species present, according to the literature review. The review found studies showing that Largemouth Bass have more success foraging in moderate plant density than in monocultures and that Northern Pike, Largemouth Bass, Yellow Perch and Bluegill tend to prefer macrophytes. And while Northern Pike and Largemouth Bass may prefer macrophytes, if their preferred prey is adversely affected by an aquatic invasvie plant such as EWM, the benefits may be lost. Also, large fish may have difficulty accessing dense stands of EWM or other macrophytes.
However, the review found that studies were based on a limited number of lakes and limited in geographic scope, typically in the northern portion of the Midwest and in the southern USA. The review recommended further study of fish response to habitat manipulation projects and the establishment of standardized macrophyte management methods that improve fisheries resources.

In addition to potential impacts to water quality and fish, the impacts to recreation and angling access is apparent, resulting in support of EWM control measures from lakeside property owners and the public. Sanders County’s priority areas for EWM management, which currently is carried out through the application of herbicides in early August, are boat launches and boat docks. A secondary priority are locations offshore where recreational boating or fishing may occur. Anglers have difficulty boating through areas where EWM forms large, dense beds, and typically avoid those areas. By creating boating lanes through existing large EWM beds, we plan to learn whether that can have beneficial impacts on fish populations and angler satisfaction.

Citation:
Kusnierz, Paul and Tholl, Timothy 2021. Eurasian Watermilfoil as Fish Habitat,
Montana Tributary Habitat Acquisition and Recreational Fishery
Enhancement Program Appendix B, Project Completion Report
(Draft). Avista Natural Resource Office, Noxon, Montana.

• Increase edge habitat for Largemouth and Smallmouth Bass, Northern Pike, Yellow Perch, Pumpkinseed and non-game species by 217,800–290,400 linear feet;
• Improve fishing access and experience in Noxon Reservoir by opening up boat lanes through large infestations of Eurasian Water Milfoil (EWM) and increasing angling opportunities particularly for Largemouth and Smallmouth Bass in those areas;
• Reduce amount and density of Eurasian Watermilfoil by 15-20 acres.

Project Objectives are to:

• Boater Access: Increase boater access by opening up 15–20 acres of otherwise weed-choked reservoir surface with boat lanes of an estimated 108,900–145,200 feet in length and 6 feet in width; The access lanes will be within two EWM beds of approximately 30–40 acres in area combined.

• Habitat: Increase edge habitat for targeted sport fishes (Largemouth and Smallmouth bass) by 217,800–290,400 linear feet; This will be an increase from virtually no edge habitat within the interior of the EWM beds.

• Sport Fish: A measurable increase in abundance of Largemouth and Smallmouth Bass in the project area. Length and weight will also be recorded to determine if there is any measurable difference of fish in treated beds versus control beds.

• Invasive Species: Reduce EWM 40–60 percent of bed size, resulting in a decrease of an estimated 15–20 acres of EWM; The treatments will be within two EWM beds of approximately 30–40 acres in area combined.

• Angler Satisfaction: Increased catch rate of Smallmouth Bass and Largemouth Bass in treated area compared with control area.

We will use a mechanical harvester (contracted over two seasons) to create openings in two beds of milfoil and follow up with extensive monitoring of amount of EWM removed, the abundance and condition of fish, as well as angling success. Both the treated and control beds will be sampled to evaluate fish response and EWM growth. EWM will be measured prior and post mechanical treatment, and over time to determine the effectiveness of the harvesting method. Also, monitoring of the beds prior to and after mechanical harvesting will estimate fish abundance and diversity, as well as length and weight. While fish size and condition will be documented, we are not establishing target values because we are uncertain whether this project will yield any clear results in that regard.

In addition, angling success will be evaluated with the intention of improving the sport fishery. The numbers and species of fish caught by anglers will be determined in the treated areas, compared with the control areas. Based on the outcome of this research, mechanical harvesting of EWM may continue to be employed as a fisheries management tool. If mechanical harvesting of EWM results in a desirable amount of control, and boat launches and other high use areas can effectively be cleared of EWM, then it may eventually be used along with or instead of herbicides.

Permits needed for this pilot project include a Stream Protection Act 124 permit from MFWP. The 124 permit will be secured at least two weeks prior to the project’s start date. In addition, MFWP and the Task Force must complete an Environmental Assessment (EA) under the National Environmental Protection Act and the Montana Environmental Protection Act. A draft EA was distributed for public comment in April 2021. A Record of Decision on the EA is expected in 2021, which will cover the project period.

EWM Monitoring
• Prior to treatment all plots will be sampled using rake tosses. Field rake toss locations will be established in GIS by a applying a grid to locations within the plot perimeter identified during previous survey efforts. At least two points per acre will be sampled. Additional or fewer locations will be sampled if the extent of the bed is substantively different from the previous MFWP survey.

• Locations sampled will attempt to capture the shape of the bed. The perimeter of the beds will be recorded in a GPS unit and the addition or removal of rake toss locations will be done in the field based on the measured perimeter of the EWM bed at the time and the established grid on the GIS maps created prior to the rake toss sampling.

• Rake toss samples will be performed by dropping a rake attached to a telescoping pole to the bottom on one side of the boat and rotating the rake 720 degrees. The rake will be retrieved, and the percent fullness estimated for all aquatic vegetation, just EWM, and just curlyleaf pondweed (CLP). This process will be repeated on the other side of the boat. The two rake fullness estimates will be averaged and a cover class assigned to that point. In addition, at each rake toss location, distance from top of EWM to reservoir bottom will be measured. Cover class associated with the rake toss estimates will be consistent with current surveys conducted by MFWP as part of the Task Force herbicide treatment program.

• Immediately following the treatment of a plot with the harvester (the same day), each rake toss location from the pretreatment EWM sampling will be visually inspected and scored as either EWM present (harvested) or absent (not harvested). The percentage of “present” rake toss locations will be divided by the total number of pretreatment locations to serve as verification that enough EWM had been harvested. If the treated estimate and the rake toss location estimate are not within 10% of each other, the path widths and lengths will be verified to ensure the appropriate amount of EWM is removed. If necessary, additional treatment will be performed.

Fish Monitoring:
• Pretreatment fish sampling will consist of electrofishing. Electrofishing will consist of making a single 50 m pass at three evenly-spaced locations around the perimeter of each EWM bed. Every fish that can be captured will be identified to species, weighed (g), and measured for total length (mm). In addition, location, date, time, water temperature and personnel will be recorded. Fish will be anesthetized to accurately identify, measure, and weight fish. Fish will be held in aerated tanks during the entire capture process. After being processed, fish will be released at the center point of the transect that was electrofished. GPS coordinates will be collected for each electrofishing path.

Angler Survey:

Details for the angler survey are under development. Generally, the goal is to determine if anglers are more satisfied with the access and fishing quality in the modified EWM beds than in the control areas. MFWP and Avista will partner with the Montana chapter of B.A.S.S. Nation and the Task Force to develop a plan for evaluating angling experience. The plan outline is to recruit experienced anglers to fish the control and treatment beds such that an even amount of time is spent fishing control versus treatment beds during the same time of day. Anglers will be asked to record the date, weather, beds fished, the time fishing began and ended at each bed, the species targeted, the species and length of each fish caught, perception of the treatments (beneficial, neutral, negative), and suggestions to make the beds more accessible and desirable for fishing. The survey will be conducted both in 2022 and 2023 following the mechanical treatment.

Monitoring Schedule:

2022:
• June–early July – pretreatment sampling of EWM and fish
• July – EWM treatment and visual monitoring of treatment areas
• July–September: Angler Surveys
• August–September – post-treatment sampling of EWM and fish

2023:
• June–early July – pretreatment sampling of EWM and fish
• July – EWM treatment and visual monitoring of treatment areas
• July–September: Angler Surveys
• August–September – post-treatment sampling of EWM and fish

Outreach efforts will address the need to share information with the public about the pilot project and information specific to anglers. The Task Force will provide in-kind assistance to produce and distribute outreach materials. Specifically, we plan to:
• Work with the Task Force and Montana B.A.S.S. Nation to keep stakeholders informed of the progress and enlist their support and assistance;
• Prepare press releases for distribution in the summer of 2022 and 2023 to inform the public about the project, its purpose and results, and acknowledging the role of project partners and funders;
• Provide signage at public access points on the Noxon Reservoir, with acknowledgement of project partners including Friends of Reservoirs;
• Post press releases on the County’s Task Force website;
• Other measures as appropriate.