Henrys Lake Newsletter – Winter 2024/2025

Henrys Lake anglers, let’s get you caught up on recent happenings, this year’s stocking report, and much more. We’ve been busy this season, and there’s a lot to share. Let’s get into it! But first, a brief fishing report.

Fishing Report

The lake ice-capped this year on November 19, and we’ve been building ice ever since. In most places, we’re up to ~11 inches of ice, but several pressure ridges are running throughout the lake with some thinner spots near springs, so be careful! Fishing was good on first ice, with several people reporting excellent catch rates from the Outlet, State Park, and Hatchery. Catch rates have slowed considerably since then, but folks are still reliably catching fish at the Hatchery and State Park. With light snow loads, access to the State Park and Cliffs has remained open, but those locations will likely be inaccessible by wheeled vehicles soon. As access becomes more limited, don’t be afraid to go for a walk to get away from crowds, and drill several holes to find the edges of weed beds. The shallows (~2ft of water) produce fish much more reliably than people think, so don’t be afraid to try close to shore. Folks are having more success with subtle presentations lately, such as tungsten teardrop jigs tipped with plastics/bait, or worms rested on the bottom. 

Remember, the trout harvest season on Henrys Lake closes on February 14th! Henrys Lake is catch-and-release only from February 15 through the Friday before Memorial Day weekend. 

2024 Stocking Report

Henrys Lake is heavily supplemented by hatchery-reared fish. 100% of the hybrid cutbows (HYB) in Henrys Lake are hatchery-origin, and ~90% of the Yellowstone Cutthroat Trout (YCT) are hatchery-origin. It’s a little harder to determine what proportion of our Brook Trout (BKT) are wild vs. hatchery-origin, but we can say confidently that at least 45% of the BKT in Henrys Lake are stocked fish.

With the Henrys Lake fishery being so reliant on stocked fish, we need to stock at high densities to achieve catch rate goals. Every year, we routinely stock >1 million trout into Henrys Lake. With recent declines in our gill-net catch rates (read all about that here), we stocked more fish in 2024 than we have since 2010 (Figure 1). In total, we stocked 1,594,000 fish into Henrys Lake in 2024, including 1,286,000 YCT, 201,000 HYB, and 107,000 BKT (Figure 1). 

In addition to increasing stocking numbers to compensate for lower catch rates in recent years, we’re conducting a number of stocking strategy evaluations to identify ways to bolster recruitment (i.e., the proportion of fish that survive to a catchable size) of our stocked fish. We know that recruitment of each year class varies considerably, but it’s extremely difficult to pinpoint what factors contribute to annual recruitment variability. While we can’t change things like water temperature, annual snowpack, water level, or water chemistry/quality, we can change things like timing, location, and fish size-at-stocking. In 2024, we stocked ~70,000 YCT into Henrys Lake tributaries (Targhee Creek, Duck Creek, and Timber Creek; pictured below), and we will be comparing survival of those fish to the survival of our lake-stocked fish in the coming years. We’re also changing the timing of our HYB stocking. Since 2019, we’ve stocked most of our HYB in June, but have observed poor recruitment of HYB since that change. In 2025, we’ll be reverting to our original strategy of stocking all our Henrys Lake fish in September. 

Another important component of stocked fish survival can be their size-at-release. Unfortunately, IDFG hatchery space is limited due to demands from other fisheries, and it’s difficult to conduct size-at-release studies in-house when considering the quantity of fish needed for Henrys Lake. We are currently working with Henrys Lake Foundation to explore solutions to this problem, and greatly appreciate their willingness to help us go beyond our normal scope and find answers to these important questions!

Current and Upcoming Projects

Creel Survey: This year (6/1/24 – 6/1/25), we are running a creel survey! Twice a week, creel clerks will be out interviewing anglers about their fishing trip that day. These data are vital for estimating total fishing effort, harvest rates, angler demographics, opinions, and much more! If you encounter one of our creel clerks, the survey should only take a couple of minutes and we greatly appreciate your participation. If you’re interested in getting involved, volunteering as a creel clerk is an easy way to do just that! Send me an email at Nathan.Tillotson@idfg.idaho.gov and we’ll get you trained up. 

Lower Targhee Creek: Over the past two years, IDFG, Henrys Lake Foundation, and other partners have been working with motivated landowners on lower Targhee Creek to plan, fund, and implement 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. Phase 1 of this project was scheduled to break ground this year, but got held up due to some permitting red tape. We’re back on track to complete phase 1 in Summer 2025! This phase will provide ~1.5 miles of additional spawning habitat for YCT in lower Targhee Creek, as well as improve hyporheic flow, groundwater recharge, wetland function, and expand oxygen/thermal refugia for trout in Henrys Lake. This project would not have been possible without generous contributions from both the landowner and the Henrys Lake Foundation, so they deserve a huge shout out here!

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: Is the extended ice fishing season the reason for catch rate declines in Henrys Lake? 

Answer: 

All our research points to “no” – there is no evidence that the extended season on Henrys Lake has contributed to lower catch rates. Instead, our data indicates that we have a variable recruitment problem, which we are working on solving with stocking strategy evaluations as explained above.  However, this is a simple question with a complicated answer. 

Throughout the history of the recreational Henrys Lake fishery, harvest has never been a factor contributing to trout relative abundance in the lake. However, harvest is not the only way anglers can influence whether a fish lives or dies. Post-release fishing mortality is a real thing that should be accounted for if deemed significant for that waterbody/species. Until recently, we didn’t know what post-release ice fishing mortality was like in Henrys Lake. The information I’m sharing below is somewhat of a repeat from a previous “Ask a Biologist” segment, but this is still by far the most asked question I receive from concerned anglers. 

In the winters of 2021 and 2022, we conducted a post-release ice fishing mortality study on Henrys Lake. For full study details, click here, but I’ll give you a brief summary in this newsletter. We used anglers of all skill levels to capture 161 trout through the ice at Henrys Lake – all using the same bait and barbed hooks. We held those fish in spawn shed at the Henrys Lake hatchery for three weeks to monitor post-release mortality before releasing them back into the lake. At the same time, we allowed 151 trout to swim up our fish ladder and into the spawn shed voluntarily to act as our control group. None of the fish in the control group died, and only one of the fish in the ice fishing group died. That’s 100% survival of our control group, and 99.4% survival of our treatment group. The only fish that died in the treatment group was dropped on the ice a couple of time by the angler, leading us to believe that handling is much more important than whether or not the fish was caught and released through the ice. Regardless, the difference in mortality between the groups was negligible, and we can confidently say that catch-and-release ice fishing does not influence trout mortality in Henrys Lake. 

If harvest doesn’t contribute to trout population declines, and post-release mortality doesn’t contribute to trout population declines, I can confidently say that the extended fishing season on Henrys Lake does not contribute to trout population declines.