Henrys Lake Quarterly Newsletter - January 2021

Henrys Lake Quarterly Newsletter

January 2021

Many of you may have noticed that the hatchery has been closed to the public and our IDFG presence has been reduced around the lake this season. In response to guidance from Idaho Department of Health and Welfare, all IDFG hatcheries remain closed across the state to limit the risk of transmitting the COVID-19 virus to both department staff and local residents until further notice. Our goal is to continue to serve our sportsmen and women while keeping safety at the forefront of our work.

Each year we stock Henrys Lake with three species of trout. In June 2020, we stocked approximately 191,444 Hybrid Trout (Rainbow x Yellowstone Cutthroat Trout) at ~3 inches in length. This past September we stocked 1,049,850 Yellowstone Cutthroat Trout at ~3” in length and 110,180 Brook Trout at ~5.5” in length.

That’s a total of over 1,351,400 trout!

In the fall of 2019 we began a stream flow project on Rock Creek which included the installation of two diversion structures on this tributary of Henrys Lake. This past October we completed this project by installing flumes to help reduce stream bank erosion and allow for the accurate measurement of water being diverted from Rock Creek. These diversions were installed through a collaboration with the U.S. Forest Service, Henrys Lake Foundation, IDFG, and multiple landowners. The aim of the project was to keep more water in the stream by providing landowners with the tools to know more precisely how much water is being diverted to their properties for irrigation and livestock.

We installed head-gates and flumes at two diversion locations on Rock Creek. Rock Creek is a tributary of Duck Creek which flows directly into Henrys Lake and is an important Yellowstone Cutthroat Trout spawning tributary. We are hopeful that more cold, well-oxygenated water will remain in the stream during critical summer time periods for Cutthroat because these new diversion structures will allow water users to more precisely manage the amount of water diverted. More summer flows in Rock and Duck creeks will improve habitat for Yellowstone Cutthroat Trout in the system.

               
               

         Left: Upper diversion structure and flume          Right: Lower diversion structure and flume

Darcy McCarrick, a graduate student with the Idaho Cooperative Fish and Wildlife Research Unit and the University of Idaho has been conducting research on the interaction between Utah Chubs and Yellowstone Cutthroat Trout in Henrys Lake over the last two years.

The influence of Utah Chub (UTC) on Yellowstone Cutthroat Trout (YCT) is largely unknown, but they can have negative effects on salmonids in systems where they have been introduced. As such, we are very interested in how UTC and YCT interact in Henrys Lake.

During the spring of 2019 and 2020, a total of 94 Yellowstone Cutthroat Trout and 95 Utah chub were surgically implanted with radio telemetry tags. Fish were relocated via mobile tracking from a boat throughout the summer, and via boat and airplane during fall and winter.

To find out more about this project, check out the 2019 results here:
https://mailchi.mp/01cdd8843410/henrys-lake-newsletter-december-2019

and the 2020 results here:
https://mailchi.mp/46fc24704416/henrys-lake-newsletter-september2020

The amount of oxygen in water is crucial to the survival and health of trout. When oxygen levels decline, a fish becomes stressed and its body cannot perform to its full potential. As such, the more oxygen there is available in the water column the better trout health and survival can be. Each winter we track oxygen levels under the ice by measuring the amount of dissolved oxygen throughout the water column at multiple locations on the lake. We use these data to make predictions about oxygen levels for the remainder of the winter. This information is useful in planning and preparing for our spawning operations which typically occur in February. In the graph below you can see that oxygen levels for this season are projected to be significantly higher than we observed during the 2019-2020 winter at this time of year. This is positive news for the fishery meaning trout health and survival should be relatively good this winter.

We will continue to monitor these oxygen levels throughout January. If these oxygen levels follow our projections, we expect high overwinter survival for trout currently in the lake which translates to more fish in the lake for you to catch!

This past year, COVID-19 has created many challenges for each and every one of us. One thing is for certain, this year has highlighted how important outdoor opportunities are to help us step away and recharge even if just for a few hours.

Many anglers took the time to get away this winter and fish the hard water at Henrys Lake.

But how was the fishing, you ask?

During the 2020 Ice fishery we interviewed 154 anglers. Of these anglers, 80% were Idaho residents while 20% of interviewed anglers were from out of state. Anglers fished the hard water for an estimated 69,144 hours of total effort. This is twice as many hours fished compared to the 2019 ice fishing season (34,511 hours). On average, anglers caught approximately 0.4 trout/hour which is less than the catch rate observed in the 2019 ice fishery of 1.28 trout/hour.

Anglers caught an estimated total of 27,756 trout over the season and harvested 6,172 of these trout. This indicates anglers harvested 22% of the trout that they caught. Yellowstone Cutthroat Trout were the most commonly caught fish at 46% of the catch, followed by Hybrid trout at 42% and Brook Trout at 12%.

When compared to the most recent open water fishery survey conducted in 2019 anglers harvested a similar proportion of fish they caught. During the open water fishery in 2019, anglers harvested 14% of the fish they caught, while ice anglers during the 2020 season harvested 22%. Henrys Lake anglers released most of the fish they caught, and the number of fish harvested is lower than anticipated to cause negative impacts to the population number or average fish size in the lake.

Overall there was increased angling pressure on the lake this past ice season but anglers were not as successful as 2019.

1. 2020 spawn: Each year we spawn Yellowstone Cutthroat Trout and Yellowstone Cutthroat x Rainbow Trout Hybrids at Henrys Lake in February and March. We fertilize the eggs and incubate them on site before shipping them to other IDFG hatchery facilities where we raise them to fingerling sizes. These fish are then stocked back into the lake in the spring and fall. Check out the video below to see how we spawn trout at Henrys Lake.
2. Gillnetting: Our annual gillnet survey takes place just after ice-off (April/May). Information gathered from this survey allows us to monitor trends in the abundance, size, age structure, and survival rates of trout and chubs in Henrys Lake.

Our next quarterly newsletter will be sent out in April 2021 so stay tuned!
If you have any questions, thoughts or concerns please contact the Henrys Lake Biologist Jenn Vincent at jenn.vincent@idfg.idaho.gov.