Henrys Lake Quarterly Newsletter - April 2021

Henrys Lake Quarterly Newsletter

April 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.

This spawn season was certainly one for the books. We operated as a small crew who remained on call for the month of February and March. We operated the trap from January 22 through March 3, 2021 and we were able to trap 7,221 unique fish.

Yellowstone Cutthroat Trout
This year we collected an estimated 2,080,890 fertilized Yellowstone Cutthroat Trout eggs over 3 days. These eggs were incubated on site at the Henrys Lake facility for approximately 28 days before they reached their "eyed up" stage. At this stage you can look at the egg and see two little black eyes of the fish inside. If you look long enough you can even see them moving inside the egg! Check out the picture below, can you see the eyes?

Once they have reached this stage, staff sort through the eggs removing any impurities or eggs that were not fertilized. Next the eggs are counted and transported to the Mackay Hatchery where they will finish incubation, hatch, and grow to fingerling trout before being stocked back in to the lake this September.

Check out the video below to see us live in action spawning Yellowstone Cutthroat Trout in 2020.

Hybrid Trout (Yellowstone Cutthroat Trout x Rainbow Trout)

Creating a sterile Hybrid Trout is a collaborative effort between multiple hatcheries and involves a time-sensitive "recipe" that staff need to follow down to the second.

On a hybrid spawn day, staff at the Hayspur hatchery start their day in the wee hours of the morning collecting milt from male Rainbow Trout broodstock on site at the Hayspur hatchery. Milt from each individual male is bagged, put on ice and driven over 3.5 hours to staff at Henrys Lake. At Henrys Lake, staff will collect eggs from female Yellowstone Cutthroat Trout and fertilize the eggs with the Hayspur Rainbow Trout milt. Next the eggs are washed, and disinfected at certain time points following fertilization to clean off the excess milt and limit fungal infections. Next these eggs undergo a pressure-shock treatment for 5 minutes at 9500 psi. This high pressure interrupts cell division in the egg and creates what is referred to as a triploid fish which are unable to reproduce. By stocking the lake with sterile Hybrid Trout we can provide anglers with the opportunity to catch some trophy trout and multiple trout species in the lake while protecting our native Yellowstone Cutthroat Trout genetics and spawning habitat.

This year we collected and fertilized an estimated 926,810 Hybrid Trout eggs over 2 days. These eggs will then go through the same process as described above for the Yellowstone Cutthroat Trout before travelling to the American Falls hatchery to finish incubation, hatch, and grow to fingerling trout to be stocked back into the lake in June 2021.

Over the past two years, historical environmental and biological data have been compiled and processed. These data include air temperature, reservoir volume, stocking rates, catch rates of each species, and hard structures from Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri. Hard structures, such as scales and otoliths, form rings that mark annual growth similar to tree rings. This allows biologists to estimate age by counting the total number of rings and evaluate annual growth by measuring the distance between rings (increments). Check out Figure 1 below, and try your hand at counting the rings.

Growth of the hard structure is proportional to the growth of the fish and the increments can be used to estimate lengths at previous ages. Back-calculated lengths at age of Yellowstone Cutthroat Trout were compared across decades (Figure 2). Two interesting patterns were revealed by this comparison. First, we noticed increased variation in size at age through time. The second pattern is that Yellowstone Cutthroat Trout in the most recent two decades are slightly larger on average than Yellowstone Cutthroat Trout in the past.

Growth was further evaluated with mixed effects modeling. This technique produces growth coefficients that represent growth of all Yellowstone Cutthroat Trout sampled each year. Due to concerns with estimates from scales, growth coefficients were only calculated for years we had otolith data (1994 – 2019). Growth patterns were cyclic and have improved in recent years (Figure 3).

1. 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.
2. Henrys Lake Opener: If you are like me you are eagerly awaiting the Henrys Lake opener! This year the lake will open to fishing on Saturday May 28th, 2021. Our staff will be around the lake on opening day weekend conducting a creel survey. We will interview anglers to better understand the current state of the fishery and how fishing is on the lake. Keep an eye out for staff, we would love to talk with you all.
3. Electric fences: Each June, through a cooperation with multiple landowners and ranchers we install miles of electric fencing along Duck, Howard, Targhee, and Kelly Creeks and along the lake. These fences help to keep livestock out of the riparian areas of Henrys Lake tributaries and off the shoreline of Henrys Lake. By limiting access to these important tributaries by livestock we can protect vital in stream habitat for Yellowstone Cutthroat Trout.
4. Fry Traps: This year we plan on reinstalling fry traps in the main tributaries of the lake. Our goal is to capture fry that have emerged upstream and are travelling to the lake. Through the collection of DNA via a fin clip we will be able to identify if these fry are from spawning wild or hatchery Yellowstone Cutthroat Trout. The number and identity (wild vs. hatchery) of these fry will provide us with valuable insight into the current wild contribution to the lake and amount of successful spawning occurring at Henrys Lake.

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