Outdoor Idaho

On the Henry's Fork

Interview with the Biologist: Dr. Rob Van Kirk


What if someone told you that much of what we think we know about the Henry's Fork is based on myth? And what if that person were a respected biologist?

Dr.Rob Van Kirk is the Research Director for the Henry's Fork Foundation. OUTDOOR IDAHO interviewed him in the summer of 1996.


OUTDOOR IDAHO: What is it that most people don't realize about the Henry's Fork?


It's really been a revelation to a lot of people to learn that this famous river was stocked with hatchery fish and the fish population was maintained by hatchery fish. That's probably been a bigger revelation than that rainbows aren't native. Those two things have been nothing short of earth-shattering for many people.
OUTDOOR IDAHO: When, in recent memory, was the fishing the best on the Henry's Fork?
In the early seventies the river was stocked with hatchery rainbow trout quite heavily: 30,000 fingerlings and 30,000 catchable trout per year... In 1970 the operation at Island Park dam was changed; they used to shut it off. They'd turn it off at the end of irrigation season and when it filled in the spring, turn it on again, and so the survival of fish over the winter was really lousy.

Once they turned that water on in the winter, survival of the fish went way up and habitat conditions improved. Around that time the Harrimans donated the land to the state, so it became public for the first time in eighty years.

Flyfishing was just beginning its modern rennaissance in this country, and the flyfishing writers came to the Henry's Fork. It was the first time they were able to walk down to some of this water to fish it.There were huge rainbow trout and tons of insects, and the next thing you know there were articles in the national magazines that the Henry's Fork was THE place; and it really was, from 1976 til about 1983.

I came here in 1977, and started working with Mike Lawson, and the fishing was better than anything I'd ever seen. But a bunch of things happened in the late seventies that in retrospect we can say were responsible for a decline in the trout population.


OUTDOOR IDAHO: What happened?
Special regulations were put on the river in 1978, which changed it from a local hatchery-supported fishery with a six fish limit to a slot limit: you could keep three under twelve and one over twenty. So the angling clientele shifted from 70% local to 70% out-of-state. Most of them were people catching and releasing, but when they did that they quit stocking the river.

But they still had problems getting young fish to survive the winter, and limiting that input of fish from the hatchery caused the fish numbers to go down.

If you look at the population trends over the last twenty years, they just go down, down, down, until it hits rock bottom in 1992. And then we had the sediment incident in 1992.


OUTDOOR IDAHO: In 1992 over 50,000 tons of sediment from the Island Park Dam landed in the Henry's Fork when they lowered the reservoir. What effect did this have on the fish?
Ironically, the '92 drawdown was the only bright spot in the population trend over the last twenty years, because a large number of reservoir fish came into the river, about ten to fifteen thousand fish. So, instead of 3,000 fish in Box Canyon, we had 11,000 fish.

It was kind of a mixed blessing, I guess. It compromised some features in the river -- there were undoubtedly some places in the river where the sediment filled in a lot of spaces along the banks where the young fish seek cover -- but on the other hand, fishing would have been pretty lousy in 1993,'94 and '95. Unfortunately, what we're seeing is that, from that peak, we've seen a steady decline year by year since then.

This reinforces what our research has been showing us: that the limiting factor in this river is recruitment of young fish into the population, and we're sort of heading back down to what the river can sustain naturally without any input from the hatchery or the reservoir.


OUTDOOR IDAHO: If the fish numbers are steadily dropping, is there a solution?
We're putting a lot of hope on a fish ladder on the Buffalo River. When the Island Park dam was built, there was also one put on the Buffalo River. When we look at this river system as a whole, a lot of the spawning occurs in the tributaries, not in the main river. Hopefully, we'll get fish from the Henry's going up the Buffalo, and we figure there's five or six miles of very high quality spawning and rearing habitat on the Buffalo. It's a spring creek; it comes out of the ground, at a constant 52 degrees. In fact, the fish grow faster and have a higher survival rate than the main river. We're hoping that it will give us another 4,000 three year old fish in the Henry's Fork.

If that doesn't work, I don't know what we'll do. But we need to increase the recruitment of young fish into the river. The adults do great. There's a lot of food for them, but the young fish have a hard time in here.

We're also thinking that one hundred years of intensive cattle grazing has resulted in the loss of riparian vegetation all along the river. Young fish utilize overhanging willows, so one of the things that could significantly help us out is to revegetate all these banks. At some point you may see us planting willows.


BACK TO HENRY'S FORK BACK TO OUTDOOR IDAHO