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The Upper Henry’s Fork Project: uncovering the diamond in plain sight


Since 2018, PhD student Jack McLaren (that’s me!) has been working with the Foundation to understand what restricts fisheries production and ecosystem health in the Upper Henry's Fork River from Big Springs to Island Park Dam. With support of our wonderful members, we’ve collected quite a bit of data over the past three years. What we’ve found so far has changed our understanding of Island Park Reservoir and the Henry’s Fork upstream of Island Park Reservoir. More importantly, results from this project are supporting our efforts to conserve, protect, and restore trout and salmon habitat in the Henry's Fork River. After three long years of data collection—rain or shine—I’m very much looking forward to telling the story of this project and our results. To start off, here’s a “bird’s eye”, five-minute overview of the project. Enjoy, and stay tuned for future blogs about what we've done and what we've found!

Two men in wetsuits wading in a clear stream
The Author (Jack McLaren, left) and HFF Staff Scientist Bryce Oldemeyer (right) hard at work during a snorkel survey. Image credit: Christina Morrisett

The Issue:

The Henry’s Fork River and its tributaries upstream of Island Park Dam are beautiful streams in a beautiful setting, with some of the best invertebrate diversity and abundance and best water quality in the entirety of the Henry’s Fork, and yet fishing conditions don’t always seem to match. Why is that?

A forested river with clouds and sky reflected in the water
The beautiful Upper Henry’s Fork near Mack’s Inn. Image credit: Jack McLaren

Multicolored line graph of scientific data
Water temperatures at the Flat Rock Sonde just downstream of Highway 20 near Mack’s Inn for June-September 2021 (black line) with average water temperatures between 2014 and 2021 (gray line). Red, yellow, yellow/green, light green, and green polygons represent lethal, stressful, semi-stressful, sub-optimal, and optimal conditions for rainbow trout. Water temperatures remain optimal for the majority of the usually-stressful summer period. See more data like this at the following:

The problem:

There are a significant number of recreational floaters in this area, but there is little evidence that these floaters are having a negative impact on fish populations. For example, there are plenty of recreational non-angling floaters in Box canyon and Warm River stretches, and yet those fisheries still support excellent angling. The fact is, we don’t know much about the Upper Henry’s Fork or the “bottlenecks” that constrict total fish numbers and fish habitat in the Upper Henry’s Fork.

A man holds a fish in front of a river with kayakers
The problem is this: how do we make more of these quality fish in the first place? Answering this question could help improve the fishery even with recreational use. Image credit: Jack McLaren

The Solution:

A solution can be found in the work the Henry’s Fork Foundation has done in other parts of the Henry’s Fork Watershed. For example, in the Henry’s Fork in the Harriman Ranch we know that the critical bottleneck is winter flows; more winter flows = more fish. Add in spring freshets which lead to more bugs (see Bryce’s excellent blog), and we have a fairly good understanding of what it takes to grow more and bigger fish (and have better fishing) in the Henry’s Fork downstream of Island Park Reservoir. We’re adopting the same approach of using data and science to find bottlenecks and create effective and efficient conservation programs to alleviate those bottlenecks in the Upper Henry's Fork. The Henry's Fork Foundation used your donations leveraged with federal and state competitive grants to fund a PhD student at Utah State University (USU) to find out what the critical bottlenecks are for fish in the Upper Henry's Fork and Island Park Reservoir.

A man standing in a river with scientific instruments
The author, Doctoral Research Associate Jack McLaren, tests water near the North Fork Club for its alkalinity, turbidity, temperature, and nutrient content. Results of these analyses help identify what, if any, fundamental building blocks of life—i.e. nutrients and carbon—might be limiting factors for plants, trout, bugs, and other living things in the Henry’s Fork upstream of Island Park Reservoir. Image credit: Natalie Pontikes

The benefits:

The big benefit of understanding the bottlenecks of trout and salmon numbers and habitat is that knowing the limits to a system can help managers and others to take action to remove those limits and end up with more and bigger fish.

A man standing in a river holding a fish
The author, Doctoral Research Associate Jack McLaren, holding an 18 inch long kokanee salmon fair-caught with hook and line from the Henry’s Fork River upstream of Island Park Reservoir. Kokanee in the Henry’s Fork upstream of Island Park Reservoir provide some fun variety in the fall time, so long as runs are good enough. A typical kokanee salmon ranges from 12-18” at maturity, while fish in the Henry’s Fork are large: 16-22” with some approaching 24”. Improving numbers of these fish would benefit anglers and the ecosystem. They are not only fun to catch but their eggs and flesh are important food sources for other fish. Image credit: Julie McLaren

So what?

Why focus on this part of the Henry’s Fork when there are already other parts of the river that need our attention? Beyond the obvious aesthetic attraction of the Upper Henry's Fork—it is truly a captivating place—the Upper Henry’s Fork is a true spring creek. It arises from Big Springs, which is itself a true wonder as one of the largest springs in the western United States. Spring-fed, high-elevation systems like the Upper Henry’s Fork are more resilient in the face of drought, warming temperatures, and development. Understanding and conserving these systems can provide a bulwark against fish habitat loss elsewhere. Also, understanding how nutrient releases from new wastewater treatment infrastructure could affect fish and fish populations will be one of many important side-benefits of studying the Henry’s Fork upstream of Island Park Reservoir.

It doesn’t hurt that despite the challenges, the Upper Henry’s Fork and Island Park Reservoir show flashes of potential in its fishery. Responsibly targeting pre- and post-spawn fish running out of Island Park Reservoir (while avoiding redds) can provide fruitful days catching a mix of rainbow trout, cutthroat trout, brook trout, kokanee, and whitefish, depending on the season. Island Park Reservoir contains some truly large trout and plenty of room to spread out. Figuring out how to improve the fishery while simultaneously managing current threats could help produce yet another place to catch trophy fish and explore new sights and experiences in our beloved Henry’s Fork Watershed.

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