A number of years ago, I had the opportunity to fish several trout streams around West Yellowstone, MT, including the Yellowstone River in Yellowstone National Park. At that time, fishing for native …
A number of years ago, I had the opportunity to fish several trout streams around West Yellowstone, MT, including the Yellowstone River in Yellowstone National Park. At that time, fishing for native cutthroat trout was excellent, at least from what I observed. We fished the Yellowstone a few times on that trip, mostly in the evening, and it wasn’t difficult to hook several cutthroats in the 18- to 20-inch range. I made that trip again in 2002, and fishing for cutthroats remained excellent.
Soon after, friends that continued to go west and fish the Yellowstone heard reports that the cutthroat population was in decline; they reported to me that the fishing was off. At the time, rumor had it, lake trout had been found in Yellowstone Lake and were preying on young cutthroats, having a serious impact on cutthroat population. When I heard that lake trout were the cause of the cutthroat decline, I wondered how that species got into Yellowstone. Lake
This is what I learned: Around 1890, lake trout were initially stocked by the U.S. Fish Commission (now the U.S. Fish and Wildlife Service) in Lewis and Shoshone lakes, which are both in Yellowstone Park. Records indicate that lake trout were first found in Yellowstone Lake in 1994. Chemical analysis of the ear bones (otoliths) determined that the lake trout in Yellowstone Lake were descendants of the lake trout population found in Lewis Lake. How lake trout from Lewis Lake ended up in Yellowstone Lake remains a mystery. One theory is that lake trout were introduced to Yellowstone Lake from illegal stocking by fishermen. In my view, as a fisheries biologist, this seems very unlikely. First of all, lake trout are a deep-water species, not easily caught by anglers. In addition, several large, sexually mature individuals would have to have been caught, safely transported, then released into Yellowstone Lake.
According to the Yellowstone Park map, Lewis Lake is about 10 miles from Yellowstone Lake. That means, if anglers transported lake trout from Louis Lake to Yellowstone Lake, they would have needed a very large container of cold water that was supplied with oxygen. Lake trout spawn at five to seven years when at an average length of 14 to 17 inches. So, fairly large specimens would have been necessary to start a viable population.
Lake trout (Salvelinus namaycush) are not true trout but actually members of the char family, which include; brook, bull, Dolly Varden and arctic char. Lake trout are the largest species of salmonid fish in the world, with specimens attaining weights of well over 70 pounds. They are voracious predators and feed on whatever variety of fish species are present. In Yellowstone Lake, lake trout are at the top of the food chain, creating havoc for the native Yellowstone Lake cutthroat population. For example, park biologists found that, in one tributary flowing into Yellowstone Lake where 70,000 cutthroats spawned in 1978, only 500 showed up in 2007. In addition, biologists also determined that only about 10 percent of the estimated three to four million cutthroats survived the lake trout’s onslaught, the first decade after discovery.
When National Park Service (NPS) biologists confirmed that lake trout were reproducing in Yellowstone Lake, they called together a panel of experts to assess the problem and find solutions. Those experts recommended the removal of lake trout by gillnetting and trap netting, advising that, while both were effective methods, they would involve an ongoing, perhaps neverending commitment toward eradication. In 2008, NPS biologists once again sought the advice of fisheries professionals in an attempt to further reduce lake trout numbers; they were told to continue with the netting and to increase efforts. So Hickey Brothers, a commercial gillnetting company, was hired to take on the task. In the last 25 years, Hickey Brothers removed almost four million lake trout from Yellowstone Lake.
More recently, biologists were able to locate some of the actual spawning areas used by lake trout by tagging adults with radio telemetry devices. About 14 spawning areas were found. Soon after, biologists learned that when the remains of lake trout were ground up and spread around the spawning areas, bacterial decomposition of the meat depleted oxygen around the spawning beds, suffocating the eggs. A promising new treatment involves releasing pellets made of soy and wheat on the spawning areas, where bacterial decomposition, once again, decreases oxygen levels, causing lake trout eggs and embryos to suffocate. Those 14 spawning areas cover less than five percent of Yellowstone Lake’s total area. More spawning areas must be found if this method is going to become an effective way of control.
On the positive side, in 2018, NPS heard that cutthroats were once again spawning in remote tributaries of Yellowstone Lake. They traveled into the area, did some fishing and caught more than 100 cutthroats in a four-day period! They were joined by a film crew on the trip, which made a short documentary titled “The Return,” a tribute to the positive impact the lake trout eradication program was having on the Yellowstone Lake cutthroat trout population.
At this time, it appears that the effort made by NPS, researchers and gillnetters is having a positive effect on the Yellowstone Lake cutthroat population. Nevertheless, if history is a reminder, once an undesirable species finds its way into an ecosystem, control is a long-term, perhaps never-ending proposition. Credit must be given to all those dedicated folks who worked so diligently to help restore this very unique and very valuable fishery resource. Once in a while, the good guys win, even when it comes to invasive species.