SUMMER 2023 UPDATE YELLOWSTONE LAKE CUTTHROAT RECOVERY

By DAVE SWEET

Wyoming Trout Unlimited Yellowstone Lake Special Project Manager and WYTU board member

It has been a while since I have provided an update to the entire Wyoming Trout Unlimited community on the status of Yellowstone Cutthroat trout recovery in Yellowstone Lake — a couple years, in fact. You may have wondered if the effort is continuing. I assure you that it is and with some very good news.

The National Park Service (NPS) has remained absolutely committed to suppressing the lake trout population, to the tune of spending about $3 million a year for the past several years. The Hickey Brothers gill-netting remains the cornerstone of the effort and is supplemented by NPS crews doing telemetry studies to locate the invasives which helps in placing the nets in optimal locations while also conducting spot suppression with gill nets.

The National Park Service (NPS) has remained absolutely committed to suppressing the lake trout populations, to the tune of $3 million a year...

The graphs (Figures 1 and 2, below and upper right) show the overall gill-netting effort along with the total number of lake trout removed per year. The gill-netting effort has remained at about 90,000 units and the total number of lake trout removed remains high but is declining.

The most significant development of the past few years of gillnetting, however, is the precipitous decline in the number of adult (age 6+) lake trout left in the system. The netters have consistently targeted these highly predacious older fish which are the ones responsible for the reproduction. Lake trout don’t spawn until they are 5-6 years old.And, small lake trout don’t prey on the

See YELLOWSTONE LAKE PROJECT on page 7 cutthroats.As shown on Figure 3 (previous page, bottom right) the current adult lake trout population in the lake is now about 10 percent of what it was just 10 years ago. system. Suppression will have to continue in order to protect the native fish population and keep the lake trout from rebounding. But the scientists tell us that suppression can be reduced in the next couple years (perhaps by one third) and the fisheries balance maintained. The NPS is committed to that strategy

That doesn’t mean that all age classes are in this same steep decline. Lake trout, like any suppressed fish population, has an amazing ability to successfully spawn and succeed in the survival of eggs to young fish. The phenomenon is called compensation. Lake trout in Yellowstone Lake have certainly exhibited this compensation as the NPS saw large numbers of young fish from the 2018 and 2019 spawning years (see Figure 3). Those fish are currently 4-5 years old and are being aggressively targeted by the gill-netters. Subsequent spawning years after 2019 have not shown the same level of compensation probably due to the continuing drop in adult lake trout numbers.

The result of these many years of lake trout suppression has been the increasing survival of cutthroat in the lake. While no specific population estimates of cutthroat numbers have been recorded; population trends are readily available from numerous studies. Each shows the same trend – the cutthroat are rebounding in good numbers. Whether it is from spawning tributary assessments, or angler surveys, or distribution netting; the results are the same. Yellowstone cutthroat numbers are rebounding and have surpassed recovery objectives. The following graph of the past 50 years of cutthroat population assessment tells a very encouraging story. The cutthroats are back.

Meanwhile, technology continues to evolve. Perhaps one day, the “silver bullet” will be found that can totally remove lake trout. In the meantime, Yellowstone Lake and its river system provides some of the best Yellowstone cutthroat trout fishing to be found anywhere. Make that trip and find out for yourself.

Yellowstone Lake, 1980–2022. Horizontal lines represent the primary (solid line) and secondary (dashed) conservation targets (desired conditions) for cutthroat trout following the suppression of invasive lake trout. Data points represent the average catch-per-unit-effort (C/f) of cutthroat trout each year. Special thanks to Dr. Christopher Guy, U.S. Geological Survey, Montana Cooperative Fishery Research Unit,for creating this figure.

And, obvious to anyone who has fished the system in the past several years, the average size of the cutthroats is truly impressive. If you haven’t fished Yellowstone Lake in the past few years, you are missing out. Fish like this are the norm. Even bigger examples can be caught. My personal best is a robust 27-inch fish. Do yourself a favor and plan a trip to the Yellowstone Lake or River system.

So, what does the future hold for Yellowstone Lake? With today’s technology, the lake trout will never be extirpated from the

Yellowstone Lake Project photos and graphs courtesy of Dave Sweet, Wyoming Trout Unlimited