Yellowstone lake trout suppression program

Gillnetting has removed over 3 million lake trout since , of which roughly 2 million have been removed over the past six seasons, during the period Yellowstone Forever has supported the increased effort. How do we know the efforts are working to increase the cutthroat populations?

All indicators—such as an increase in spawning fish in tributaries, a three-fold increase in juvenile fish within the lake, and higher catch rates by cutthroat anglers throughout the lake ecosystem—are all strong evidence that cutthroat trout numbers are up. Angling on the lake has been increasingly good over the last five years, especially after spring thaw.

However, despite the massive removal effort, lake trout are still in Yellowstone Lake in large quantities, and NPS employs adaptive management to continue to improve the approach. All of the data collected is put into models, which are then reviewed by a scientific panel each year to help better understand the present situation and inform decisions for future years.

To complement the gillnetting, other suppression efforts will help maintain low levels of lake trout. Recently, the placement of lake trout carcasses over the spawning areas has proven to be an effective method of killing the lake trout eggs.

The lake trout that are killed each summer are returned back to deep areas of the lake, thus putting those nutrients back into the ecosystem. Most of the fish caught have been dead for days by the time the nets are pulled in, and are not edible. Yellowstone Forever supports this priority park program by raising annual funds to help cover expenses. Nov A Race Against Time. Carty, R. Gresswell, D. Mahony, and S. Fishery and aquatic management program in Yellowstone National Park. Jordan, D.

A reconnaissance of streams and lakes of Yellowstone National Park, Wyoming in the interest of the U. Fish Commission. Bulletin of the U. Fish Commission Kaeding, L. Waterbirds Boltz, and D.

Lake trout discovered in Yellowstone Lake threaten native cutthroat trout. Fisheries Bethesda Kendall, W. The fishes of the Yellowstone National Park. Bureau of Fisheries, Document , Washington, D. Kiefling, J. Jackson Lake completion report. Koel, T. Arnold, P. Bigelow, P. Doepke, B. Ertel, and M. Ertel, and D. Nonnative lake trout result in Yellowstone cutthroat trout decline and impacts to bears and anglers.

Mahony, K. Kinnan, C. Rasmussen, C. Hudson, S. Murcia, and B. Myxobolus cerebralis in native cutthroat trout of the Yellowstone Lake ecosystem. Journal of Aquatic Animal Health Martinez, P. Bigelow, M. Deleray, W. Fredenberg, B. Hansen, N. Horner, S. Lehr, R. Schneidervin, S. Tolentino, and A. Western trout woes. Mattson, D. Influences of cutthroat trout Oncorhynchus clarki on behavior and reproduction of Yellowstone grizzly bears Ursus arctos , — Canadian Journal of Zoology McDonald, M.

Report of the United States Commissioner of Fish and Fisheries for the fiscal years and Government Printing Office, Washington, D. Middleton, A. Morrison, J. Fortin, C. Robbins, K. Proffitt, P.

White, D. McWhirter, T. Koel, D. Brimeyer, W. Fairbanks, and M. Grizzly bear predation links the loss of native trout to the demography of migratory elk in Yellowstone. Moore, H. Cope, and R. Yellowstone Lake creel censuses, Munro, A. McMahon, and J. Natural chemical markers identify source and date of introduction of an exotic species: lake trout Salvelinus namaycush in Yellowstone Lake. Canadian Journal of Fisheries and Aquatic Sciences Murcia, S.

Kerans, E. MacConnell, and T. Myxobolus cerebralis infection patterns in Yellowstone cutthroat trout after natural exposure. Diseases of Aquatic Organisms Reinhart, D. Bear use of cutthroat trout spawning streams in Yellowstone National Park. Pages in L. Darling, and W. Archibald, editors. Rieman, B. Gresswell, and J. Fire and fish: a synthesis of observation and experience. Pages in C. Luce, P. Morgan, K. Dwire, D. Isaak, Z. Holden, and B.

Rieman, editors. Climate change, forests, fire, water, and fish: building resilient landscapes, streams, and managers. Ruzycki, J. Beauchamp, and D. Effects on introduced lake trout on native cutthroat trout in Yellowstone Lake. Ecological Applications Schaller, G. The conservation of the white pelican in Yellowstone Lake.

Simon, J. Yellowstone fishes. Swenson, J. Prey and foraging behavior of ospreys on Yellowstone Lake, Wyoming. Journal of Wildlife Management Alt, and R.

Ecology of bald eagles in the Greater Yellowstone Ecosystem. Wildlife Monographs Syslo, J. Guy, and B. Comparison of harvest scenarios for the cost-effective suppression of lake trout in Swan Lake, Montana. Varley, J. Ecology, status, and management of the Yellowstone cutthroat trout.

Freshwater wilderness: Yellowstone fishes and their world. The Yellowstone Lake crisis: confronting a lake trout invasion.

Socioeconomic values associated with the Yellowstone Lake cutthroat trout. Pages in J. Varley, and P. Three important metrics were assessed for lake trout: total annual mortality in the population, abundance, and population growth rate. A catch-at-age analysis based on the age structure of the total catch of lake trout removed by the suppression program, and the effort used to do so each year, was conducted to estimate lake trout mortality and abundance. In addition, a model based on mortality and several other population descriptors e.

This model also estimates the amount of netting effort needed to achieve a population decrease. In combination, the analyses and modeling results provide rigorous estimates of how successful the program has been at decreasing lake trout in Yellowstone Lake.

Increased Efforts to Suppress Lake Trout Multiple scientific reviews stressed that substantial suppression of lake trout was necessary for the cutthroat trout population to recover. In , removal efforts were increased dramatically in order to drive the lake trout population growth rate from one that had been increasing for over a decade to one that is decreasing Syslo et al.

Hickey Brothers Research, LLC, a company with roots in commercial fishing on Lake Michigan, was tasked with the bulk of the suppression work, operating three full-time boats designed specifically for gillnetting. Crews work six days per week from late May into early October, with each crew setting and retrieving 60 nets per day.

Letting each net soak, or catch fish, for nights allows each crew to handle nets twice a week. Figure 2. Each line approximates one gillnet set; the darker the color, the more lake trout caught per night fished. Thus, the amount of gillnet in the water on a typical mid-season day increased from almost 23 km 14 mi. Total gillnetting effort increased from an average of 20, units m of net set over one night constitutes one unit of effort from to to an average of 65, units from to In , gillnet suppression effort increased to 79, units; netting was expanded into the South and Southeast arms of the lake, areas that previously received relatively little effort figure 2.

Plans are to continue netting effort during and beyond. The latest population modeling suggests at least 55, units of netting effort is needed each year to suppress the lake trout population; we intend to expend approximately 80, units. A large number of lake trout 2, were captured, marked with numbered tags monofilament inserted between the bones of the dorsal fin with a T-bar similar to clothing tags , and released.

Tagged fish later caught in suppression nets or via angling were documented and used to estimate the number of lake trout present in the lake; the derived estimate was , fish greater than mm 8.

The mark-recapture study also enabled an estimate of the probability of capture for four size classes. These results supported previous estimates and highlight the difficultly in catching older, larger lake trout which eat the most cutthroat trout. Older, larger lake trout also have the highest reproductive success. Lake Trout Response to Increased Suppression Efforts In , we experienced our highest lake trout suppression effort, along with the highest number of lake trout removed, to-date figure 1.

Catch per unit effort remained relatively low, indicating crews had to work harder and smarter to catch the same number of fish. Increases in catch and catch per unit effort can reflect increased efficiency, increased abundance, or both. Improvements in fishing gear, increased knowledge of how lake trout use the ecosystem, and experienced personnel can lead to increases in catch and catch per effort despite a decreasing population.

Hence, independently monitoring the effectiveness and results of suppression activities, as well as updating population models, is an important aspect of the program. Models have shown the lake trout population continued to expand through at least , but increased netting since then has begun to reduce lake trout numbers and biomass total weight in Yellowstone Lake.

Abundance estimates for lake trout age 2 and older indicate a cessation of population growth and a decrease in fish older than 2 years figure 3. As this continues, the reproductive and expansion potential of the population will be reduced, greatly aiding overall suppression. In addition, the total biomass of lake trout removed has been well above what is considered a sustainable harvest 0.

Figure 3. Abundance estimates for 2-year-old and year-old lake trout in Yellowstone Lake, Future Outlook The magnitude of the lake trout problem in Yellowstone Lake remains enormous. Lake trout have had several decades to expand throughout the lake and pioneer several spawning areas.

Yellowstone Lake provides near-perfect spawning and rearing habitat for lake trout with few natural predators present. Lake trout are longlived, and one individual female can produce thousands of eggs each year. The survival of young lake trout in the lake is estimated to be 2. Even without cutthroat trout, other foods in Yellowstone Lake would support a large lake trout population.

Reducing the lake trout population to a level that will have only minor impacts to the cutthroat trout population is predicted to take until at least , provided we maintain current high levels of suppression effort.

Compared to other lakes invaded by lake trout in the West, Yellowstone Lake has a relatively simple fish assemblage. Only two species, cutthroat trout and lake trout, occupy the vast majority of the habitat; however, they segregate into different depths or water temperatures of the lake most of the time.

Thus, the solution is deceptively simple: decimate the lake trout population while not adversely impacting Yellowstone cutthroat trout. Reviews of the program over multiple years by multiple fishery scientists, along with in-depth population modeling, continue to emphasize this resource issue can be solved given sufficient suppression effort. In fact, recent monitoring suggests both the abundance of older lake trout and the biomass of lake trout removed has been decreasing since With planned increases in suppression netting for coupled with emerging technology for killing lake trout eggs and embryos, a population crash is expected to happen sooner than population models suggest.

However, until new methods can be verified, netting suppression of lake trout in Yellowstone Lake must continue and is widely supported by anglers, fishery experts, and park managers. Thus, suppression efforts will continue in an attempt to restore a robust native Yellowstone cutthroat trout population in Yellowstone Lake.

Literature Cited Bigelow, P. Koel, D. Mahony, B. Ertel, B. Rowdon, and S. Protection of native Yellowstone cutthroat trout in Yellowstone Lake, Wyoming. Crait, J. River otters in Yellowstone Lake depend on a declining cutthroat trout population.