Fish within the Esocidae family are among the most sought after freshwater sportfish in North America and are widely viewed as a premier trophy fish. Tiger Muskellunge (Esox masquinongy x E. Lucius), a sterile, hybrid fish produced by crossing Muskellunge (Esox masquinongy) and Northern Pike (Esox lucius), is a particularly fast-growing esocid because no energy is spent on reproduction. Tiger Muskellunge provide a unique opportunity for natural resource managers to create trophy fishing opportunities without the risk of establishing an unwanted naturally reproducing population while simultaneously taking advantage of their piscivorous nature to control nuisance or overabundant fish populations. However, because of their solitary and sedentary behavior, Tiger Muskellunge are a difficult species to manage. Traditional fishery monitoring techniques estimate population abundance and demographics as a snapshot in time and space and rely on large sample sizes. The combination of low capture rates and spatial segregation typically found with Tiger Muskellunge limits fishery-independent data and can restrict the ability of managers to make informed management decisions. Acoustic telemetry has gained widespread popularity as a tool to understand migration, habitat use, and survival of aquatic animals. Acoustic telemetry functions similarly to radiotelemetry in terrestrial environments; an animal-borne tag transmits an acoustic signal detected by a receiver, which in this case is an underwater hydrophone. Compared to capture-recapture studies where numerous animals are tagged in hopes that a small proportion of tagged individuals are observed later, acoustic telemetry provides an abundant and continuous stream of detection data and spatial movements across multiple years without the need for recapture. Furthermore, once an array of acoustic telemetry receivers is deployed, multiple studies can be conducted on various species to rapidly increase the number and quality of inferences the researcher can extract from the detection data. Acoustic telemetry is a powerful tool to gather fine- and broad-scale data on fish movement, habitat requirements, and responses to environmental change. Improving population estimates and understanding behavioral traits are important for ecosystem-based management in aquatic environments and can help managers better understand how species respond to environmental changes (e.g., seasonal drawdowns and habitat loss), intraspecific competition (e.g., resources and space), predator-prey dynamics, and refine population size estimates to inform stocking strategies. Pineview Reservoir, Weber County, Utah is a popular warm-water fishery that experiences significant seasonal drawdowns. The Tiger Muskellunge population at Pineview Reservoir is considered a trophy fishery; however, monitoring of Tiger Muskellunge is not conducted regularly because of the difficulty associated with sampling, and angler catch rates and satisfaction are declining. Tiger Muskellunge at Pineview Reservoir has traditionally been stocked at a high density of 50-mm fingerlings. Recent drought years have reduced the availability of nearshore nursery habitats and may have limited the survival of fingerling Tiger Muskellunge. UDWR managers are developing an adaptive stocking model to adjust the size-at-stocking (50 vs 200-mm fish), stocking frequency, and time of stocking (spring vs summer) by accounting for key physical and biological attributes limiting the growth and recruitment of juvenile Tiger Muskellunge. However, the behavior, habitat use, intraspecific competition among age-classes, and mortality of Tiger Muskellunge are not known. Additionally, part of this project will be to add more habitat to promote the recruitment of young of the year (YOY), age 1, and adult Yellow Perch, Perca flavescens, Black Crappie, Pomoxis nigromaculatus into Pineview Reservoir. Dramatic fluctuations in reservoir levels and fall turnover create situations that make survival very low for YOY, age 1, and adult fish. This additional habitat will increase the probability for these fish to overwinter and stabilize the panfish population in the reservoir.

1) Establish an acoustic telemetry array within Pineview Reservoir and perform range detection 2) Develop protocols for intracoelomic implantation of acoustic transmitters in Tiger Muskellunge 3) Quantify post-stocking survival rates of juvenile Tiger Muskellunge 4) Evaluate dispersal and habitat use of newly stocked juvenile Tiger Muskellunge 5) Calculate seasonal movement, residency patterns, and home ranges of adult Tiger Muskellunge 6) Estimate demographic parameters (e.g., population size, mortality rates, carrying capacity) 7) Provide managers insights on spatio-temporal movements and habitat use to improve catch rates with traditional sampling gear 8) Increase additional habitat options for YOY, age 1, and adult Yellow Perch and Black Crappie. 9) Stabilize population fluctuations by recruiting additional panfish each year into the reservoir which will provide additional angling opportunities.

Pineview Reservoir is an impoundment of the Ogden River with a surface area of 11.6 km2, a normal operating depth of 25.0 m, and a mean depth of 13.4 m. The primary fish community is comprised of black bullhead (Ameiurus melas), black crappie (Pomoxis nigromaculatus), bluegill (Lepomis macrochirus), largemouth bass (Micropterus salmoides), smallmouth bass (M. dolomieu), tiger muskellunge, and yellow perch (Perca flavescens). Fish community sampling occurs on a two-year rotation and Tiger Muskellunge are stocked on an annual basis. Pineview Reservoir consists of three inlet forks and one outlet fork, with each inlet fork physically isolated by peninsulas from the others and all forks converging in the center of the reservoir (see attached map). The reservoir shape is ideal for acoustic telemetry studies as the geographical barriers between reservoir forks prevent individuals from being detected in multiple forks and allows for broad-scale spatial and seasonal movements to be monitored with a limited number of receivers. An acoustic array within each fork would allow researchers to quantify habitat use, spatial overlap of conspecifics, and seasonal migration behaviors. The morphology of the outlet fork is steep with limited shoreline habitat; therefore, we propose to not deploy receivers in this fork of the reservoir as suitable habitat for juvenile Tiger Muskellunge is not present. Recent drought conditions have greatly reduced water volumes among reservoirs within the Weber River drainage. Pineview Reservoir dropped to levels not seen in over two decades. High summer water temperatures and low water levels have eliminated shoreline habitats and nursery grounds typically accessed by Yellow Perch, Black Crappie, and Tiger Muskellunge. During seasonal drawdowns, deep-water, artificial habitats can provide invaluable resources for escaping predation and increasing survival in the forage fish community. UDWR has been installing artificial habitat structures within Pineview Reservoir since 2018, has observed the success in forage fish survival, and sees the need to include more in the reservoir.

The following objectives are found in the Utah Tiger Muskellunge Management Plan: 1. Objective A.6, C.6.G - Maintain and improve the quality of stocked and wild fish populations in Utah. This objective will be addressed by identifying post-stocking survival rates and population dynamics of juvenile Tiger Muskellunge to inform optimal stocking densities and stocking strategies (i.e., size-at-stocking, stocking frequency). Additionally, we can improve the robustness and precision of ongoing capture-recapture studies to greatly improve the quantitative methods for assessing Tiger Muskellunge stocks. 2. Objective C.6, R.2.F - Establish quantifiable desired habitat conditions and develop standardized habitat monitoring procedures. Apply these procedures to establish baseline habitat conditions before restoration work and repeat these assessments after work is completed so success can be evaluated. Adapt management approaches based on monitoring conditions. This objective will be addressed by linking juvenile Tiger Muskellunge presence to specific physical and habitat components to guide habitat development plans and ensure suitable nursery habitat is present as reservoir levels fluctuate. Additionally, by incorporating adult Tiger Muskellunge we can identify critical habitat use across life stages. These next plans are from working documents in regional work plan efforts. Constituency goal: C.6 -- Increase hunting and fishing opportunities. Improved access and additional fishing opportunities for anglers Increased participation in fishing within the Northern Region. Reduce habitat fragmentation and reconnect fish populations F-Perform 5 habitat improvement projects annually to increase fishing access , habitat quality and sustainability Increased fishing success for anglers Improved watershed, ecosystem and stream health Improved fish populations in systems where habitat is limiting Maintain and strengthen relationships with private landowners, Trout Unlimited, NRCS, DWQ and other key partners R.2 -- Maintain existing wildlife habitat and increase the quality of critical habitats and watersheds throughout the state Improved fish populations in systems where habitat is limiting Maintain and strengthen relationships with private landowners, Trout Unlimited, NRCS, DWQ and other key partners Leverage ability to get work done through those relationships

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We propose to deploy acoustic arrays, one within each outlet reservoir fork, for a total of 12 receivers (Innovasea NexTrak R1) systematically placed throughout the reservoir. Receivers will be suspended 2 m from the bottom of the reservoir with a 50-m snag line stretched along the bottom of the reservoir for retrieval. A temperature logger will be attached to each receiver. Receivers will need to be serviced (i.e., battery change, data download) annually. Tiger Muskellunge are produced annually by the UDWR and raised in a hatchery setting up to 200 mm in length prior to stocking. We propose to tag 75 juvenile Tiger Muskellunge (150-200 mm total length) prior to stocking with one of the smallest commercially available acoustic transmitters (Innovasea V8-4x; 8 mm diameter; 20.5 mm length; 2.0 in air; >400-d tag life) to increase post-stocking survival. Individuals will be selected haphazardly from their rearing tank. Each fish will be measured, sexed, and tagged with an intramuscular external tag located near the posterior edge of the dorsal fin. Fish will be anesthetized (Aqui-S 20E), placed supine on a surgical board for tag implantation, and incisions closed with a synthetic absorbable monofilament. Tagged juveniles will be monitored for 1-week in a hatchery raceway, accessed for incision healing, inflammation, and tag retention, and then transported and dispersed throughout the reservoir. Additionally, we propose to tag 20 adult Tiger Muskellunge collected by the Utah Division of Wildlife Resources via boat electrofishing and local Muskies, Inc. chapter members captured by hook and line. Adult Tiger Muskellunge will be tagged with a larger acoustic transmitter (Innovasea V13-1x; 13 mm diameter; 31.5 mm length; 9.4 in air; >1800-d tag life) to increase tag life and study duration. Tagged adults will be held in an aerated tank until individuals are recovered. All field tagging events will be conducted when water temperatures are below 20C to facilitate incision healing and minimize infection. All surgeries will be conducted by a single trained researcher. Once habitats are received and transported to the reservoir, groups and individuals will assemble these habitats. Assembled habitats will be transported to a designated area marked by a minimum of four buoys. Larger habitats (i.e. Mossback) will be placed in the center and smaller habitats (i.e. Pond King) will surround them. These habitats will be randomly spread throughout the designated drop area. This area will be at a depth which still had plenty of water in 2021 during the lowest reservoir elevation levels seen in the past 20 years.

Protocols for intracoelomic tag implantation will be evaluated based on the survival, degree of healing, and tag retention rate after the 7-day hatchery holding period. Individuals that do not meet criteria for release will be euthanized and tags will be removed and deactivated for future use. Additionally, the intramuscular external tag will allow for long-term incision healing and the condition of tagged fish to be monitored during angler captures. Detection data will be downloaded from the receivers annually. Post-stocking survival will be evaluated as the proportion of individuals surviving through the first growing season. Individuals will be assumed to be alive until one of the following events is observed and considered to be a mortality: (1) the total cessation of detections after clear evidence of movement; (2) the beginning of a gap in detection history spanning at least 4 months, with no clear evidence of movement; or (3) the beginning of a long string of detections at one or very few adjacent receivers (e.g., 3 months) as a dead fish or a tag resting on the bottom near the receivers), with no subsequent evidence of movement. A set of linear mixed-effect models will be used to quantify seasonal and inter-annual changes in detections within and among the reservoir forks. Daily presence/absence at each receiver will be analyzed as a binomial response variable, sex and tagging location or release location as fixed effects, and total length at tagging, age of fish, water temperature, monitoring year, and day of year as random effects. A movement matrix will also be used to quantify the degree of connectivity between receivers and regions of the reservoir. This matrix will be used to create weighted and directed seasonal networks for each tagged individual that reflects the extent of space and habitat used during the entire monitoring period and the relative importance of each habitat occupied. Habitat use by above mentioned fishes, will be conducted during the fall and winter months via boat using sonar to graph habitats and fish. During the winter, sonar used for ice fishing purposes will also be used to detect fish using the structures. An ROV may also be used during these times to capture live video of the structures and any fish around them.

Muskies Inc US Forest Service Weber Basin Water Conservancy District

1. Expand sample sizes of tagged Tiger Muskellunge and tag fish across multiple years 2. Implant tags with environmental sensors (e.g., depth, temperature) to identify vertical migration and critical environmental thresholds 3. Use predation tags to quantify predation on juvenile Tiger Muskellunge 4. Tag forage fish species to assess artificial habitat use with a fine-scale acoustic telemetry positing array 5. DWR will continue to monitor Yellow Perch and Black Crappie using Fyke and gill nets per sampling protocol. New habitats will continue to be deployed in the Middle and North Arms of the reservoir in future years

DWR will use data collected to improve stocking estimates, install more habitat structures if needed, and continue to assess the sustainability of this fishery. Collecting this data for TMK will provide DWR with better managing capabilities. The panfish species also using the habitat structures to avoid predation will survive at higher rates and produce more forage for TMK and better angling opportunities into the future.

07/01/2024

06/30/2025

2025

The acoustic telemetry portion of this project included range testing, study design, equipment purchasing, receiver deployment, and initial transmitter implantation. In fall 2024, testing showed that acoustic receivers could reliably detect signals up to 600 meters--200 meters less than originally planned. Based on this, UDWR biologists and Muskies Inc. designed a hybrid array to track fine-scale movement in Pineview Reservoir's middle arm and broader movement in the north and south arms. In spring 2025, 20 receivers and 95 transmitters were purchased, and anchoring devices were built. All receivers were deployed between May 29 and June 2. A fishing event on May 30 brought 18 boats and nearly 40 volunteers, but only four Tiger Muskies were caught, with three of those fish receiving transmitters. Follow-up electrofishing by the UDWR added nine more implanted fish. Efforts were paused in June due to warm temperatures and the risk of excessive handling stress and infection but will resume in September. So far, 11 of 12 implanted fish have been confirmed alive and moving, showing the surgeries were successful and protocols safe. Seventy-five juvenile Tiger Muskies are also part of the study and are being raised at the UDWR Fountain Green Hatchery. As of August 4, they are about 60% of the size needed for tagging. They are expected to be implanted with acoustic transmitters and released by October 2025. The habitat portion of this project involved purchasing, mapping, assembling, and placing 98 habitat structures in the middle arm of Pineview Reservoir. These structures were arranged in several small groups, covering about two acres of the reservoir. UDWR began purchasing and receiving materials in January 2025, and by May, technicians had started assembling the habitats ahead of deployment. The habitats were transported using several trucks, a horse trailer, and two boats, and were placed in approximately 70 feet of water while the reservoir was at full pool and spilling. Placement followed the same depth as previously installed habitats. On May 23, 2025, a crew of UDWR biologists, technicians, and volunteers successfully assembled and deployed all 98 structures.

Acoustic telemetry is a tool that uses sound signals to track fish. It helps researchers learn where fish move, what habitats they use, and how they respond to changes in their environment. This information can improve population estimates, show how fish compete for space and food, and guide stocking and habitat decisions. Pineview Reservoir is a popular warmwater fishery that goes through big seasonal water drawdowns. The Tiger Muskie population there is managed as a trophy fishery, but it is hard to monitor because these fish are difficult to catch and sample. In recent years, angler catch rates and satisfaction have been going down. By tracking fish with acoustic telemetry, we can learn more about their movements and habitat needs, which will help ensure suitable habitat is available for both young and adult fish as water levels change. This will also make the population more resilient over time. Testing at Pineview showed that receivers can only detect transmitters up to 600 meters, about 200 meters less than expected. Because of this, a hybrid tracking design was chosen. This design combines detailed tracking in the middle arm of the reservoir with broader tracking across the north and south arms. It ensures fish movements are recorded even if they leave the middle arm. Using the equipment we already invested in, this approach gives us better data and will help managers make smarter, science-based decisions. UDWR has documented that young-of-year Yellow Perch and Black Crappie can use low-oxygen deep-water habitats to escape predators and forage. These areas also provide cover in fall and winter when the reservoir turns over, oxygen levels equalize, and predators gain access to smaller fish. Previous habitat installations have shown high use by fish, confirmed through underwater video, sonar, and angling, and have been very successful. This project served as a test run to see how many structures could be assembled and placed in a single day with volunteers. To my surprise, all habitats were assembled in less than two hours--the longer task was transporting and placing them in the reservoir. Because no ramp is located close to the site, travel time limited the number of structures we could place. For future projects, we plan to have volunteers bring boats to improve efficiency.

UDWR will resume Tiger Muskie collection efforts in September 2025 and will implant transmitters in the juvenile fish being raised at the hatchery once they reach the target size. All proposed fish are expected to be implanted by the end of October 2025. Data collection and receiver maintenance will continue annually through 2030. UDWR will continue monitoring the habitat structures using sonar, underwater cameras, and angling. One final effort to place a larger group of habitats is planned for the next fiscal year under WRI Project 7613.