For millennia, humans harvested Yellowstone fish for food. From the park’s inception more than a century ago, fishing has been a major form of visitor recreation. It is this long-standing tradition and integration with the parks’ cultural significance that allows the practice of recreational fishing to continue in Yellowstone National Park today. In some cases, it also contributes to the National Park Service goal of preserving native species. The biological significance of fish to ecosystems makes them an ongoing subject of study and concern.
Fish and Aquatic Species
Native Fish Species
Yellowstone’s native fish underpin natural food webs, have great local economic significance, and provide exceptional visitor experiences. Though policies of the National Park Service provide substantial protection from pollution and land-use practices that often degrade habitat, historic management efforts by the park service subjected native species to the effects of nonnative fish introductions, egg-taking operations, commercial fishing, and intensive sport-fishery harvest into the middle of the twentieth century.
To reverse declining native fish populations and loss of ecosystem integrity, the National Park Service now takes action to ensure their recovery. A Native Fish Conservation Plan/Environmental Assessment was completed in 2010. The National Park Service aims to reduce long-term extinction risk and restore the ecological role of native species, including fluvial Arctic grayling, westslope cutthroat trout, and Yellowstone cutthroat trout, while ensuring sustainable native fish angling and viewing opportunities for visitors. Scientific peer review continues to provide guidance for future efforts on Yellowstone fisheries. The National Park Service strives to use the best methods available for addressing threats, with a focus on direct, aggressive intervention, and welcomed assistance by visiting anglers.
Yellowstone Cutthroat Trout
Yellowstone cutthroat trout are the most widespread native fish in the park.
Mottled sculpin live in shallow, cold water throughout Yellowstone except the Yellowstone River above Lower Falls and in Yellowstone Lake.
Yellowstone’s minnows are small fish living in a variety of habitats and eating a variety of foods.
Suckers are bottom-dwelling fish that use ridges on their jaws to scrape flora and fauna from rocks.
About 8,000-10,000 years ago twelve species (or subspecies) of native fish, including Arctic grayling, mountain whitefish, and cutthroat trout, dispersed to this region following glacier melt. These native fish species provided food for both wildlife and human inhabitants. The distribution of native fish species was originally constrained by natural waterfalls and watershed divides. These landscape features provided a natural variation of species distributed across the landscape and vast areas of fishless water. At the time Yellowstone National Park was established in 1872, approximately 40% of its waters were barren of fish—including Lewis Lake, Shoshone Lake, and the Firehole River above Firehole Falls.
Park inhabitants and visitors fished for sustenance and survival in this wild, remote place. While most hunting was curtailed by early park management, fishing was not only allowed but encouraged. Driven by the desire to establish recreational fishing in more park waters and new technology that enabled the long-distance transport of exotic fish; Early park managers stocked fish into fishless waters, produced fish in hatcheries, and introduced several nonnative species. The majority of the non-native fish introductions were trout species (lake trout, brook trout, brown trout, and rainbow trout), but other species were also introduced.
Constrained by geography, the native fish within the stocked waters were forced to live together with the nonnatives, be displaced to downstream habitats, or die out. The ranges and densities of Yellowstone’s native trout and grayling were substantially altered. Nonnative species contributed to the decline in the park’s native fish population by competing for food and habitat, preying on native fish, and degrading the genetic integrity of native fish through hybridization. By the 1930s, managers realized the destructive impact caused by nonnative fish. As a result, the National Park Service (NPS) created a formal stocking policy to discontinue these efforts.
Even though the stocking of non-natives stopped, stocking of Yellowstone cutthroat trout from Yellowstone Lake continued both within and outside the species’ native range. Overall, from the early 1880s to the mid-1950s, more than 300 million fish were stocked throughout Yellowstone. Today, about 40 lakes have fish; the others were either not stocked or have reverted to their original fishless condition.
Influences of Some Nonnative Species
Aquatic nuisance species disrupt ecological processes because they are not indigenous to the ecosystem. Invasive organisms can cause species extinction, with the highest extinction rates occurring in freshwater environments. Aquatic nonnative species that are having a significant detrimental effect on the park’s aquatic ecology include lake trout in Yellowstone Lake; brook, brown, and rainbow trout in the park’s streams and rivers; and the parasite that causes whirling disease. Though there are other aquatic nonnative species in the park, their effects are less dramatic.
Aquatic Invasive Species
An aquatic invasive species disrupts ecological processes because it is not indigenous to the ecosystem. Invasive organisms can cause species extinction, with the highest extinction rates occurring in freshwater environments.
Non-native fish distribution and their influence on native fish are not static. While they have not been intentionally stocked since the 1930s, non-native fish continue to advance into new habitats, hybridize with, or displace native fish that previously persisted in the face of extreme environmental change for thousands of years.
Hybridization of cutthroat trout resulting from rainbow trout range expansion continues to be the greatest threat to the park’s remaining native fish populations in waters outside the Yellowstone River headwaters, Yellowstone Lake, and the Snake River headwaters.
Not all of the movement by non-native fish in Yellowstone has occurred naturally. Non-native lake trout, intentionally introduced by managers in 1890 to Lewis and Shoshone lakes, and illegally introduced (possibly intentionally) to Yellowstone Lake in the mid-1980s, first appeared in angler catches in 1994. The lake trout population expanded and over the following decade caused a rapid decline in the Yellowstone cutthroat trout population in Yellowstone Lake.
In addition to nonnative fish in Yellowstone, three aquatic invasive species are having a significant detrimental effect:
Preventing the arrival of additional aquatic invasive species is critical because eliminating them after they become established in a watershed is usually impossible and efforts to reduce their impact can be extremely expensive. Each summer a small team of park technicians inspect the crafts brought in by park visitors before they put their boats or angling gear in the water. They inspect visitor’s equipment and decontaminate it, if necessary. Such decontamination is usually adequate to prevent the entry of most aquatic invasive species.
Arrival in Yellowstone
During the late 1880s when the Army administered Yellowstone, the US Fish Commission (a predecessor of today’s US Fish and Wildlife Service) stocked nonnative fish in some park waters. These stockings comprise the first known, deliberate introductions of nonnative fish to Yellowstone. Four trout species were widely introduced—brook, brown, lake, and rainbow. Rainbow trout hybridize with native cutthroat trout, thus diluting genetic diversity. All four compete with and prey upon native fish.
Other aquatic invasive species, such as the New Zealand mud snail and the parasite causing whirling disease, probably arrived via unaware boaters and anglers carrying the organisms from other locations around the country. We may never know exactly how those species were introduced to the park, but anglers can help prevent other species from arriving.
The aquatic invasive species which pose the greatest risk to ecologic, recreational, and economic values in the Yellowstone area include zebra and quagga mussels, Asian clams, Asian carp species, Eurasian watermilfoil, hydrilla, flowering rush, and viral hemorrhagic septicemia. Fisheries biologists believe several of these species are moving toward Yellowstone.
Their arrival might be avoided if anglers remember:
Zebra mussels (Dreissena polymorpha) and closely related quagga mussels (Dreissena bugensis), collectively called dreissenids, are of particular concern given their ability to attach to watercraft, survive many days out of water, and cause irreparable harm.
Zebra mussels are native to Eastern Europe and western Asia. They were first discovered in North America in 1988 in Lake St. Clair, one of the water bodies connecting the Great Lakes. It is believed that this invasive species was introduced through ballast water discharges from international shipping.
Following their initial invasion, zebra mussels spread quickly across most of the eastern United States and Canada. Zebra mussels are inadvertently transported to new water bodies by boaters who trailer their boats between infected bodies of water.
Zebra mussels drastically alter the ecology of infested water bodies and may severely impact ecosystems. Once established, these efficient filter-feeders consume significant biomass of phytoplankton, depleting the foundation of the aquatic food web. Zebra mussels can attach to most hard surfaces, forming mats that may be up to 18 inches thick. Mussels can impact recreation activities and associated economies by covering docks, boats, and beaches; in addition to causing severe infrastructure and economic damage by blocking water supply pipes of power and water treatment plants, irrigation systems, and industrial facilities.
Zebra mussels’ native predators from Europe, certain types of birds and fish, are not present in North America. Though some ecologically similar species do exist, they do not appear to have significant impact on reducing established mussel populations.
The bighead carp (Hypophthalmichthys nobilis), black carp (Mylopharyngodon piceus), and silver carp (Hypophthalmichthys molitrix) occur in at least 24 states. They out-compete native fish, reduce forage for other fish, and can transmit disease. Silver carp are also known for their ability to jump great distances out of the water when boats travel near them, causing injury to boaters.
Silver carp are native to Southeast Asia and east Russia and were intentionally introduced into the United States in 1973 in an attempt to improve water quality, increase fish production in culture ponds, as biological control and as food fish. The species now occurs in at least 18 states and is naturally reproducing. Both the silver and the bighead carp compete for food (zooplankton) with native fish.
Black carp are native to Asia and east Russia and were unintentionally introduced in the early 1970s as a stowaway with intentionally introduced grass carp. Black carp now occur in at least 5 states. Black carp may reduce populations of native mussels and snails through predation and negatively affect the aquatic ecosystem. None of these species are currently found in Wyoming, or Montana.
These invasive species may continue to be spread intentionally or through accidental introductions as fish or fish eggs and through water currents.
Since the introduction of Corbicula fluminea to the United States in 1938, it has spread into many of the major waterways and is now found in 46 of the United States states. The species have not been completely distinguished, but most varieties are small light-colored bivalves, yellow-green to light brown in color.
The native ranges are in temperate to tropical southern Asia west to the eastern Mediterranean; Africa, except in the Sahara desert; and southeast Asian islands south into central and eastern Australia. The Asian clam is a filter feeder that removes particles from the water column. It can be found at the sediment surface or slightly buried. Its ability to reproduce rapidly, coupled with low tolerance of cold temperatures (2-30°C), can produce wild swings in population sizes from year to year in northern water bodies.
Eurasian watermilfoil (Myriophyllum spicatum) has spread to all of the United States except Hawaii and Wyoming. In 2007, it was found in Montana.
This nonnative aquatic plant lives in calm waters such as lakes, ponds, and calm areas of rivers and streams. It grows especially well in water that experiences sewage spills or abundant motorboat use, such as Bridge Bay.
Eurasian water-milfoil colonizes via stem fragments carried on boating equipment, emphasizing why boats should be thoroughly cleaned, rinsed, and inspected before entering Yellowstone National Park.
Three nonnative plankton species which can displace the native zooplankton that are important food for cutthroat trout may be on their way. These nonnative zooplankton have long spines, which make them difficult for young fish to eat.
The Yellowstone Resources and Issues Handbook, updated annually, is the book our rangers use to answer many basic park questions.
Bartholomew, J.L. and P.W. Reno. 2002. The history and dissemination of whirling disease. In J.L. Bartholomew and J. C. Wilson, ed., Whirling disease: Reviews and current topics. Vol. Symposium 29. Bethesda, MD: American Fisheries Society.
Franke, M.A. 1997. A grand experiment: The tide turns in the 1950s: Part II. Yellowstone Science 5(1).
Franke, M.A. 1996. A grand experiment: 100 years of fisheries management in Yellowstone: Part I. Yellowstone Science 4(4).
Kerans, B.L. and A.V. Zale. 2002. The ecology of Myxobolus cerebralis. In J.L. Bartholomew and J.C. Wilson, ed., Whirling disease: Reviews and current topics, 145–166. Vol. Symposium 29. Bethesda, MD: American Fisheries Society.
Koel, T.M., D.L. Mahony, K.L. Kinnan, C. Rasmussen, C.J. Hudson, S. Murcia, and B.L. Kerans. 2007. Whirling disease and native cutthroat trout of the Yellowstone Lake ecosystem. Yellowstone Science 15(2).
Koel, T. et al. 2014. Yellowstone Fisheries and Aquatic Sciences Report 2012–2013. National Park Service: Yellowstone National Park.
Lilly, B. and P. Schullery. 2000. Bud Lilly's Guide to Fly Fishing the New West. Portland, OR: Frank Amato Publications.
MacConnell, E. et al. 1997. Susceptibility of grayling, rainbow, and cutthroat trout to whirling disease by natural exposure to Myxobolus cerebralis. Whirling Disease Symposium, Logan, UT.
Murcia, S., B.L. Kerans, E. MacConnell, and T.M. Koel. 2006. Myxobolus cerebralis infection patterns in Yellowstone cutthroat trout after natural exposure. Diseases of Aquatic Organisms 71(3):191–199.
National Park Service. 2011. Native Fish Conservation Plan /Environmental Assessment for Yellowstone National Park. Yellowstone Center for Resources.
Parks, R. 1998. Fishing Yellowstone National Park. Helena, MT: Falcon.
Schullery, P. 2008. Vaguely disquieting scenes: Fishing bridge and the evolution of American sport fishing. Yellowstone Science 16(3): 24–33.
Varley, J.D. and P. Schullery. 1998. Yellowstone fishes: Ecology, history, and angling in the park. Mechanicsburg, PA: Stackpole Books.
Last updated: April 3, 2019