“I’ve heard stories of a fishkill on Henrys this spring from the long winter, can you find out more about this and report on it?” was a question sent to EastIdahoNews.com and forwarded to me.
The rumors are false.
“I did not see any evidence of a fish kill last spring,” reported Mike Wilson, owner of the Drift Lodge Fly Shop and cabin owner above the Henrys Lake Fish Hatchery. “I watched it closely as the ice broke up last spring.”
“We did not have a major fish kill on Henrys last spring,” Nathan Tillotson, a regional fish biologist that oversees the Henrys Lake fishery, told me. “We had the lowest numbers of fish caught in the gill nets that we have seen in over 30 years last spring and the recent drought has been extremely hard on area fisheries. But with lots of water and the quality of water this year, we should see a lot of improvement. If we don’t, we are going to find out what is happening.”
Where do fish kill rumors start? I guided on Henrys Lake for over 35 years and was involved with the gillnetting and spawning of fish at the Hatchery for over 20 years. During those years I have seen many ups and downs including two major fish kills, terrible fishing seasons and fantastic fishing ones.
Trout in Henrys live only about three or four years — with an occasional one living up to 11 — mainly because of their rapid growth rate and their spawning stress. Most of the spawners are three to four years old and being spring spawners, coincides with ice-out and last spring the ice came off the lake on May 19, just a week before Memorial Day. Cutthroat trout begin spawning in February and by the time the ice has receded, some of the spawners have started dying from spawning stress. Even into June, we will see evidence of spawning stress because their bodies are weakened allowing fungus patches to develop on their skin which will kill them.
The main way the Idaho Department of Fish and Game determines the fish population of the lake is by running gill nets right after ice out. They attempt to set six nets out each night until they have collected fish from 50 net-nights. This year the ice left late, so they did not get them finished until the first week of June.
“Our goal is to have 11 trout per net per night and in the last few years we have have averaged 11.3 fish until this year,” said Tillotson. “This year, our gillnet survey resulted in a capture rate of 2.9 trout per net. There’s no sugar-coating that one. It’s the lowest total trout catch we’ve observed in the last 30 years and lower than any of us would like to see.”
Tillotson went on to explain that the low numbers are probably a result of the recent drought that has “plagued the region over the last few years that is tied to a suite of uncontrollable environmental factors.” Stocking rates have basically remained the same, about 1.1 million fingerlings, but in 2023, they raised that number to 1.5 million to compensate for the loss in fish populations.
Surveys show that about 90 percent of the fish in Henrys come from the stocking, with 10 percent from natural recruitment from the streams. The key to the adult population is how many of the planted fingerlings survive that first year. Water quality and quantity are key factors, so most stocking happens before the blue/green algae bloom appears.
“Our studies show that we have a mortality rate of from 99 percent to 2 percent,” Tillotson told me. “Most years we have a mortality rate of 80 to 90 percent and then about every fifth year or so, we have one between 20 to 50 percent. When that happens, we have a lot of fish and the size drops. This year, with the low numbers we had in the lake, we had the largest average size of trout that we have ever had. The average cutthroat was 17.3 inches.”
In past years, most fingerlings were stocked at the Henrys Lake State Park, Frome County Boat Dock and the Hatchery, but this year the Fish and Game also stocked fingerlings in Duck and Targhee Creeks to see if that would result in better survival and to acclimate them to the streams.
Fall fishing on Henrys has always been one of the better times to fish the lake and this year appears to be no different. A group of fishermen who fished the lake for three days this week reported the first day they had difficulty finding the fish, the second day was “so-so” but they found a hot area. On Wednesday, they had a great day “landing 10 fish over 23 inches with one over 28 inches and a brook trout over 22 inches.”
I hope this helps some fishermen understand a little more about what is happening at Henrys Lake and that next year will be better. My hope is with all the moisture that we may even see better kokanee fishing at Ririe Reservoir also – we will just have to wait and see what happens.
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