Henrys Lake Newsletter - Fall 2023

Henrys Lake anglers, we’ve got a lot to catch up on! It’s been a busy season so far, and we have several projects in the works. Before we get into all that, I’d like to take a moment to thank the Henrys Lake Foundation for inviting me to attend and speak at their annual fundraising event. I gave a presentation about the state of the fishery and a detailed review of the results of our delayed ice fishing mortality study (more about that here). We had a productive Q&A session after the presentation, which sparked several constructive one-on-one conversations thereafter. It was a genuine pleasure speaking with so many people who have such rich histories with the lake. I’ll be sharing much of the information we discussed at that event with all of you here in this newsletter. 

Annual Population Survey

Each year, IDFG conducts a gillnet survey on Henrys Lake to assess the current state of the fishery. We begin the survey immediately after ice-out, which didn’t occur until 19-May this year (Figure 1). We set nets at six sites throughout the lake every night until we reach our goal of at least 50 net-nights of effort. Since ice-out was so late this year, we had to take a brief hiatus over Memorial Day weekend to perform our routine creel surveys but we finished the gillnet survey by June 2nd. 

This year, our gillnet survey resulted in a capture rate of 2.9 trout per net. Individual species-specific trout catch rates are as follows: Yellowstone Cutthroat Trout (YCT) = 1.7 fish per net, hybrid trout (HYB; triploid Rainbow Trout X YCT) = 0.8 fish per net, and Brook Trout (BKT) = 0.4 fish per net. There’s no sugar-coating that one. It’s the lowest total trout catch rate we’ve observed in the last ~30 years and lower than any of us would like to see. Before we move on to discuss other population metrics collected during the survey, let’s dig a little deeper into what’s going on with the low gillnet catch rates and what we’re doing about them. Drought conditions have plagued the region over the last few years and are likely to blame for the declining trend in gillnet catch rates observed over the same time frame. Fisheries all around the region have suffered similarly. Annual recruitment (A.K.A. how many fish from each year class survive from one year to the next) is incredibly variable in Henrys Lake, and tied to a suite of uncontrollable environmental factors. Despite yearly stocking rates remaining relatively consistent, we see large fluctuations in year-class strength. Through the years, stocking strategies in Henrys Lake have been altered time and time again to try to come up with the “perfect” recipe for consistently producing strong year classes of fish. However, if too many are stocked on a year that happens to have good recruitment, growth rates suffer, and we end up with a strong year-class of skinny, slow-growing fish that have to age their way out of the system before things can get back to normal. While it’s important to bring catch rates back up, it’s also important to maintain the fast growth and good fish condition that make Henrys Lake the trophy fishery that it is. We increased our stocking targets this year to compensate for low catch rates, but were cautious not to overcompensate. We increased total stocking from ~1.06 million fish in 2022 (796,574 YCT, 157,070 HYB, and 104,160 BKT) to ~1.5 million fish in 2023 (1,127,143 YCT, 255,678 HYB, and 64,777 BKT). We’ve had a good water year so far in 2023, and we’re hopeful that it will lead to good survival of these stocked fish. 

Now, let’s dig into some of the other population metrics we gathered from this year’s gillnet survey. Utah Chub (UTC) were still particularly abundant in the 2023 gillnet survey (26.6 fish per net), but have declined slightly since last year (2022 = 31.8 fish per net). On a brighter note, average size (total length) of YCT is the largest we’ve observed in at least 20 years, and the only time average size of HYB were larger than this year was last year (Table 1). You can see a full break-down of size-classes represented across the species in Figure 3. 

We also pay close attention to the body condition of our trout species in Henrys Lake. To do this, we use a metric called “relative weight” (abbreviated Wr). Relative weight for each fish is calculated based on a specific equation for that species, and a Wr of 100 indicates a fish in excellent condition (i.e. better than average). In 2023, average Wr for trout in Henrys Lake was as follows: YCT = 89, HYB = 95, and BKT = 91 (Figure 4), indicating that fish are generally in good condition and have been trending upwards over the past few years. With all these large fish in good condition, trophy potential is high! 

Current and Upcoming Projects

Electric Fences: Back in June, we installed miles of electric fence along the riparian areas of several of the Henrys Lake tributaries (Howard Creek, Targhee Creek, Duck Creek, and Kelly Creek). These fences protect the stream and riparian areas from habitat degradation. Throughout the summer, our IDFG Henrys Lake seasonal crew continually maintains these fences to ensure they remain “hot” while livestock are in the area. At the end of the season when cattle are moved elsewhere, we take down the fences for the winter to allow wildlife to freely move around the lake and tributaries. 

Fish Screen Maintenance: IDFG manages and maintains several “fish screens” located on irrigation diversions drawing water from Henrys Lake tributaries (Howard Creek, Targhee Creek, and Duck Creek). These fish screens prevent fish from being lost from tributaries, and instead, return them to the creek where they came from via underground pipes. During the runoff season, sediment builds up in the fish screens that has to be dug out weekly to ensure proper function of the screens. This August, IDFG staff tussled with a stubborn solar-powered screen with motor and electrical issues on Howard Creek, but the problems were finally diagnosed and fixed. Cows have water, and out-migrating fingerlings can make it back into the stream now! 

Lower Targhee Creek: Over the past year, IDFG and partners have been working with motivated landowners on lower Targhee Creek to assess the potential of the property for a large-scale restoration project. Targhee Creek provides incredibly valuable spawning habitat for wild YCT in Henrys Lake, as well as thermal and oxygen refuge during critical periods for fish survival. We’re very much still in the planning and pre-restoration monitoring phase of this project, but we’ve been busy gathering all the data we can (see picture of the picket weir and large hybrid below), and identifying the best ways to make this ecosystem function optimally for both fish and wildlife.

Regulatory Buoy Replacement: It’s no secret - our buoys around the fishing closures at the mouth of Hatchery Creek and Staley Springs have taken a beating over numerous years of ice sheet abuse. We’ve got a shipment of shiny new ones that have been delivered, and we’ll get those installed during ice-out 2024.  

Fish Stocking: In June, we stocked 255,678 sterile hybrid trout in Henrys Lake (Figure 5). Just earlier this month (September), we stocked 1,127,143 Yellowstone Cutthroat Trout fingerlings and 64,777 triploid Brook Trout fingerlings! In an effort to bolster survival of stocked fish and strengthen tributary returns for wild fish, a small portion of the YCT fingerlings were stocked into Henrys Lake tributaries rather than the main lake. Approximately 20,000 YCT fingerlings were stocked into Targhee Creek, and approximately 10,000 YCT fingerlings were stocked into Duck Creek. In the coming years, we hope to expand tributary stocking efforts, and evaluate relative survival/growth/recruitment of fish stocked in tributaries vs. the main lake. The fish stocked in the main lake were spread out and stocked at three locations: Henrys Lake State Park, Bill Frome County Park, and the Henrys Lake Hatchery. 

Vaulted Toilet Installation: 

Justin Langley – IDFG Upper Snake Regional Recreation Site Foreman

Henrys Lake has been a popular fishing and boating site for many years. With recent changes to the fishing regulations, it has seen a boom in popularity during the winter months. The Henrys Lake Hatchery is one of only five public access sites on the entire lake, and one of only two access sites that are actively maintained/plowed during the winter. On average, by IDFG creel data (2019-2020), this site sees 12 sportsman a day, year-round. With the growth in usage, the need became apparent for an on-site permanent vaulted toilet at the Henrys Lake Hatchery access site. There has been an ADA-compliant portable toilet in place for years but is designed to support only 10 people per week. With the support of the Fremont County Parks and Rec and the Henrys Lake Foundation, IDFG was awarded a grant to install a permanent ADA-compliant vaulted toilet with a parking pad. The new vaulted restroom will not only able to handle the extra year-round traffic but is also easier to keep sanitized and in good condition. The new vaulted toilet will be installed near the Northwest entrance of the Henrys Lake Hatchery public parking lot. Installation of the new vaulted toilet is expected, and on track, to be completed by late-September/early-October 2023.

Ask a Biologist

At the end of each newsletter, I like to have an “Ask a Biologist” section where I can help answer/explain a timely and important question I receive about Henrys Lake or the surrounding watershed. Please send me any relevant questions you may have! My email is Nathan.Tillotson@idfg.idaho.gov.

Question: 

What’s the best way for someone to get involved in conservation/management projects that benefit Henrys Lake?  

Answer: 

There are ample and diverse opportunities for people of all abilities to get involved in the natural resource conservation/management of Henrys Lake! IDFG alone has several volunteer opportunities throughout the year for folks to get involved at Henrys Lake, including (but not limited to) YCT spawning in February-March, the annual population survey in April-May, Creel Surveys over Memorial Day Weekend, tributary electric fence and fish screen monitoring/maintenance throughout the summer, and tributary surveys in the fall. Other opportunities arise frequently, including current and upcoming activities collecting pre-restoration project data on Targhee Creek. If you’d like to get involved in any of these efforts, send me an email at Nathan.Tillotson@idfg.idaho.gov, or if you’re interested in getting involved in a variety of IDFG projects contact our Volunteer Service Coordinator, Gerren Steel, at Gerren.Steel@idfg.idaho.gov and learn how to become an Idaho Master Naturalist! Other great ways to get involved or contribute are with our NGO partners, including the Henrys Lake Foundation and the Henry’s Fork Foundation. Both foundations have accomplished great things in the name of conservation in the Island Park area, and we’re fortunate to work with them on a variety of projects. Click on the hyperlinks on their names to learn how to get involved in each organization and about some of the work they’ve accomplished!