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Idaho Fish and Game

Henrys Lake Quarterly Newsletter – Winter 2022/2023

Henrys Lake
Henrys Lake


This is starting to become a trend here lately, but we have yet ANOTHER new state record fish from Henrys Lake! On New Year’s Day, young Spencer Smith caught the new certified weight state record Yellowstone Cutthroat Trout out of Henrys Lake, weighing in at 2.88 lbs, and measuring 20 in. Congrats, Spencer! 


Henrys Lake record YCT


To recap, that is the second state record set by a Henrys Lake fish in just the last three months! As you may recall from the fall edition of our Henrys Lake Quarterly Newsletter, Hailey Thomas set the catch-and-release State Record for Rainbow/Cutthroat hybrid trout back in October with a whopping 36 incher. Beyond these two recent records, Henrys Lake has the Brook Trout market cornered, with both the certified weight record as well as the catch-and-release record. In 2016, Kazen Cromar set the Brook Trout catch-and-release state record with a 22 incher, but it couldn’t top the certified weight record set by Henrys Lake angler DeVee Stratton back in 1978 with their 7.06 lb, 23.5 inch brookie! There’s no arguing it. Henrys Lake has and continues to produce big fish. 


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. This edition of “Ask a Biologist” is a bit more substantive, so it’s going to be the featured piece in the winter quarterly newsletter! Please send me any relevant questions you may have for future editions of “Ask a Biologist”! My email is


Question: With the new extended ice fishing season, will all the catch-and-release ice fishing affect populations of fish in Henrys Lake? 



Delayed Ice Fishing Mortality Study

Henrys Lake ice huts
Ice hut at Henrys Lake



            After the implementation of the regulation change that expanded the ice fishing season on Henrys Lake, many anglers expressed concern that catch-and-release ice fishing would lead to significant post-release (delayed) mortality that would affect the population. In response, the IDFG Henrys Lake team designed and implemented a study to investigate exactly that. In November and December of 2021 and 2022, IDFG staff and volunteers conducted an experiment. Here’s some preliminary results about what we found. 

Henrys Lake brook trout
Henrys Lake Technician, Andy Johnson, holding a Brook Trout captured during the delayed ice fishing mortality study.



We captured fish through the ice using terminal tackle and bait frequently used by Henrys Lake ice anglers (white 1/8 oz barbed jighead with a chunk of sucker/chub meat). We recorded the hooking placement (lip, mouth, gills, gut, external), noted whether the fish was bleeding, noted the fishing method (jigging vs. dead-stick), tagged the fish with an external T-bar anchor (floy) tag, transported them back to our hatchery facility, and held them for three weeks before releasing them back into the lake. During this time, we also allowed fish to naturally make their way up our fish ladder from the lake into our fish trap. We tagged these fish as well and held them for three weeks to act as our control group before releasing them. 

Henrys Lake Fish Biologist, Nathan Tillotson, preparing to floy tag a fish captured during the delayed ice fishing mortality study.
Henrys Lake Biologist, Nathan Tillotson, injecting a fish with a floy tag.
Floy Tag


Results and Discussion: 

            Over the two years of the study, we captured 161 fish (121 Yellowstone Cutthroat Trout [YCT], 21 Rainbow Trout X Yellowstone Cutthroat Trout hybrids [HYB], and 19 Brook Trout [BKT]) via ice fishing for our treatment group, and had 151 fish (all YCT) naturally swim up the ladder and into our trap for the control group. Within the treatment group, average sizes of YCT were 17.9 in and 2.1 lbs, BKT were 14.6 in and 1.2 lbs, and HYB were 20.1 in and 3.0 lbs. Out of all 312 fish involved in both treatment groups, 308 were released alive and well back into the lake, 3 mysteriously disappeared (the mystery was later solved), and only 1 fish died. The one mortality was a Brook Trout in the treatment group that was hooked in the mouth. It was noted in the data that there was some rough handling of this fish before it was transported back to our facility. That’s 100% survival of our control group, and 99.4% survival of our treatment group. With numbers like these, it’s not difficult to come to the same conclusions that we did. It does not appear that catch-and-release ice fishing affects fish mortality at the population level in Henrys Lake. Just be mindful of how you handle your fish if you plan to release them, and try not to keep them out of the water for too long. 

Also, for those that are curious about our disappearing fish, we found a particularly plump mink running around inside the facility where we were holding the fish. We’re not sure exactly how long he was in there, but I’d wager it was enough time to make off with exactly three of our tasty trout. 

Fisheries Biologist, Carli Baum, holding a Yellowstone Cutthroat Trout captured during the delayed ice fishing mortality study.


Current and Upcoming Projects

Winter Dissolved Oxygen Monitoring: Each winter, IDFG staff monitors dissolved oxygen levels under the ice to assess the likelihood of winter fish kill events. Oxygen levels start out high during the early ice season, but decline through the winter as the amount of snow/ice increases and inhibits light from passing through to facilitate photosynthesis. Oxygen levels have been holding strong through the first few surveys, but we will continue to monitor them throughout the ice season. 

Henrys Lake Spawn: Each “spring”, IDFG hatchery staff conducts the Henrys Lake spawn! We collect eggs and milt from Henrys Lake Yellowstone Cutthroat Trout to produce millions of fish that get stocked in waterbodies all over the state, as well as Henrys Lake itself. We also combine Henrys Lake Yellowstone Cutthroat Trout eggs with Rainbow Trout milt, and then “pressure treat” the fertilized eggs to create the famous Henrys Lake hybrids that we all love catching. This year’s spawning operations will be happening from early-mid February through the first week of March. 

Annual Gillnetting Survey: Every spring right at ice-out, IDFG staff conducts the annual Henrys Lake gillnetting survey. Information gathered from this survey allows us to monitor trends in abundance, size, growth, and age-structure of fish in Henrys Lake. This information also helps inform the stocking strategy, or if we need any changes in regulations for future years.