"Native fish cannot fulfill their ecological role in YNP if their populations are extirpated or remain decimated, hybridized, and isolated." Koel, et al., 2017
by Todd M. Koel, P.J. White, Michael E. Ruhl, Jeffery L. Arnold, Patricia E. Bigelow, Colleen R. Detjens, Philip D. Doepke, & Brian D. Ertel
In the late 1800s, the waters of Yellowstone National Park (YNP) supported an abundance of fish. Twelve species (or subspecies) of native fish, including Arctic grayling, mountain whitefish, and cutthroat trout, dispersed to this region about 8,000-10,000 years ago following glacier melt. These native fish species provided food for both wildlife and human inhabitants. At the time YNP was established in 1872, park inhabitants and visitors initially harvested fish for sustenance and survival in this wild, remote place. Soon after, popular publications describing the quality and abundance of fishing in Yellowstone began to appear. While most hunting was curtailed by early park management, harvest of fish was allowed. During those early years, sport fishing became an accepted use of resources; and the phenomenal sport fishing experience that the park provided rose in notoriety. Yellowstone’s recognition as an angling mecca was born.
Lying on a high plateau and spanning the continental divide, the headwaters of three major rivers are found in YNP: the Missouri, Snake, and Yellowstone (figure 1). The park is home to 150 lakes and 4,265 km (2,650 mi.) of flowing waters, but historically fish were not able to access all of them. The original distributions of native fish species were constrained by natural waterfalls and watershed divides, which caused a natural variation of species distributed across the landscape and vast areas of fishless water. When American naturalist David Starr Jordan conducted the first survey of fish in YNP in 1889, he found that about 40% of the park was fishless, including the upper reaches of the Bechler, Firehole, Gibbon, and Gardner rivers (Jordan 1891). Also fishless were Lewis and Shoshone lakes, most of the small lakes, and numerous tributaries isolated by waterfalls.
The huge diversity of aquatic habitats—from large rivers to tiny tributaries, immense lakes to small ponds, fish-bearing and fishless, geothermally influenced and not—supports an array of native aquatic animals. In addition to fish, the park’s waters are home to amphibians, aquatic invertebrates, fish-eating birds, waterfowl, and mammals.
Origin of the Non-native Fish ThreatSoon after the park was established, its aquatic species composition changed. This change was driven by the desire to establish recreation and sustenance fisheries in more park waters, and an emerging fish culture technology that enabled the long-distance transport of exotic sport fish. Park managers started planting native cutthroat trout in fishless waters in 1881 and were introducing non-native species into the park by 1889 (Varley and Schullery 1998). A majority of the non-native fish introductions were trout species (lake trout, brook trout, brown trout, and rainbow trout), but several other species were also introduced. By the 1930s, managers realized that non-native fish introductions caused a loss of native fish; as a result, the National Park Service (NPS) created a formal stocking policy to discontinue these efforts (Madsen 1937).
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. More than 818 million cutthroat trout eggs were shipped by rail to locations across North America. They were also stocked extensively across the park, including waters that already supported native cutthroat trout with unique genetics (e.g., Slough, Soda Butte, Grayling, and Specimen creeks).
Overall, from the early 1880s to the mid-1950s, more than 300 million fish were stocked throughout Yellowstone. As a result, non-native species became firmly established in most lakes and in larger rivers and streams; exceptions were Yellowstone Lake, the upper Yellowstone River, the upper Lamar River, the upper Snake River, and tributaries to these watersheds. Constrained by waterfalls, watershed divides, or other landscape features, the native fish within these stocked waters were forced to live together with the non-natives, be displaced to downstream habitats, or die.
Non-native lake trout, brook trout, and brown trout consume native fish and compete for resources, thereby reducing native abundance and, as occurred in the Madison, lower Gibbon, and lower Firehole rivers, completely eliminating natives (Arctic grayling and westslope cutthroat trout) from large pristine habitats in the park. Native fish losses also occur through interbreeding. Because Yellowstone cutthroat trout, westslope cutthroat trout, and rainbow trout are closely related, they can hybridize when living in the same areas. Hybrid individuals can also be capable of reproduction, further exacerbating the problem. In only a few generations, hybrids proliferated in many rivers and streams. Large areas of the park where significant hybridization has occurred include the Bechler, Gallatin, lower Lamar, and lower Yellowstone rivers, and their tributaries.
To address these threats, fisheries biologists increased monitoring and research on the status of Yellowstone fishes, which eventually led to the development of a Native Fish Conservation Plan in 2010 (Koel et al. 2010). This plan outlined a strategy for restoring the ecological role of native fishes, while continuing to provide sustainable angling and fish viewing experiences. The plan included actions to isolate, suppress, or remove non-native fish from certain areas of the park, and then restore native fish in these areas.
Ecologists and a majority of the angling community and the general public strongly supported the plan. However, some anglers and wilderness advocates were uncomfortable with portions of the plan that proposed the enhancement or installation of barriers to prevent further invasion into areas with native fishes; the removal of non-native fishes from several watersheds using fish toxins such as rotenone; and the intense netting of non-native lake trout from Yellowstone Lake, including the frequent use of motorized boats in wilderness areas. Currently, more than 300,000 non-native lake trout are captured in nets and killed each year in an attempt to increase the survival and recruitment of native cutthroat trout in Yellowstone Lake. Also, hundreds to thousands of other non-native fish are electrocuted or removed with rotenone in rivers and streams each year to facilitate the restoration and recovery of native fishes such as Arctic grayling and cutthroat trout.
Native fish cannot fulfill their ecological role in YNP if their populations are extirpated or remain decimated, hybridized, and isolated. However, there is great potential to reconstruct native aquatic communities in some headwaters areas to conditions more closely resembling their historic state (Franke 1997). Thus, managers decided to take bold actions to restore native fish communities in some lakes and watersheds where it was feasible and success was reasonably likely. These largescale restoration activities necessitate encroaching on wildlife and wilderness principles in the short term to restore a more natural system in the long term (White 2016). Indeed, some complex projects may require intensive intervention and persistent maintenance actions for many decades. In the long term, however, these actions will contribute to the National Park Service (NPS) mission of preserving native species and the ecological processes that sustain them for the benefit and enjoyment of people.
Understanding the Conservation NeedPrior to the recent implementation of large-scale restoration efforts, native river-dwelling Arctic grayling were completely absent from park waters. Westslope cutthroat trout, within its native range, remained in only a single, tiny stream known as Last Chance Creek. Yellowstone cutthroat trout faced serious threats in the waters where they persisted.
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, hybridize, or displace native fish that previously persisted 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 (figure 1). As an example, an important cutthroat trout stronghold in Slough Creek in the Lamar River watershed has been invaded by rainbow and hybrid trout in just the last 15 years; hybridization of the native cutthroat trout in this creek continues.
Not all of the movement by non-native fish in Yellowstone that has occurred recently is natural. Non-native lake trout, intentionally introduced by managers in 1890 to Lewis and Shoshone lakes, and unintentionally introduced (possibly illegally) to Yellowstone Lake in the mid-1980s, first appeared in angler catches in 1994 (Kaeding et al. 1996). The lake trout population expanded and over the following decade caused a rapid decline in the Yellowstone cutthroat trout population in Yellowstone Lake. Concurrent with cutthroat trout loss were declines in several important avian and terrestrial species near the lake and its tributaries that depended upon the cutthroat trout as a food source (see “Non-native Lake Trout Induce Cascading Changes in the Yellowstone Lake Ecosystem,” this issue). Thus, the introduction and subsequent expansion of lake trout significantly altered the natural function of the lake and the larger ecosystem (Tronstad et al. 2010). Only through direct management intervention will cutthroat trout recover, with the function of the ecosystem restored.
Conservation ApproachAs continued losses of native fish and altered ecology were realized over the past two decades, Yellowstone’s approach to native fish conservation has greatly evolved. Management now focuses on the implementation of large-scale, innovative actions to preserve and restore native fish faced with non-native threats. The success of these activities requires a broad approach; includes a wide range of partners and stakeholders; and utilizes independent scientific oversight, assessment, and project adjustments to ensure conservation goals are being met. Key aspects of the approach to native fish conservation in Yellowstone include the following:
Vision - Every activity to conserve native fish is driven by a vision to achieve a desired condition. These clearly articulated desired conditions are typically, but not exclusively, based upon conditions that existed in the past, before alteration by European American colonists and settlers. Some desired conditions do not represent a historic or natural condition, but they are the best we can achieve given existing constraints. For example, building barriers and restoring genetically-pure populations of westslope cutthroat trout and Arctic grayling to headwater refuges are primary desired conditions given the looming threats of non-native fish and climate change to these native species across their historical ranges. Because lake trout cannot be completely eradicated, restoring cutthroat trout to an abundance and population structure that existed when lake trout abundance was low (in the early 1990s), and allowing cutthroat trout to regain their ecological importance within the food web are primary desired conditions for Yellowstone Lake.
Partnership - Each aspect of native fish conservation is influenced and benefits from networking, interacting, and partnering with other agencies, conservation organizations, and interested stakeholders with similar visions and goals. Examples of strong partnerships which have resulted in significant advancements in native fish conservation activities in Yellowstone include the Montana Arctic Grayling Recovery Program, the Sun Ranch Westslope Cutthroat Trout Hatchery Program, the Rangewide Yellowstone Cutthroat Trout Conservation Team, and the Yellowstone Lake Workgroup. Formal partnerships have enabled the transfer of information and sharing of successes and failures; increased understanding and use of emerging technologies; leveraged resources, including staff time and equipment in the field; and forged development and implementation of diverse fundraising strategies. The transfer of information and communication has also occurred during public meetings held in park gateway communities each spring, which increases the public’s awareness about program activities.
Planning - The 2010 Native Fish Conservation Plan includes an adaptive management framework to guide efforts to recover native fish and restore natural ecosystem functions. Adaptive management allows for continuous learning and adjustment of actions to ensure desired outcomes are achieved. The overall goals of the 20-year plan are to: 1) reduce the long-term extinction risk for native fish, 2) restore and maintain the important ecological role of native fish, and 3) ensure sustainable native fish angling and viewing opportunities. Annually, fish conservation needs are prioritized and planning for individual projects occurs prior to the forthcoming summer. Planning involves fisheries staff, as well as staff from other workgroups within the park that provide support for fisheries operations. Projects occurring in watersheds that cross park boundaries involve staff from all affected agencies with jurisdiction.
Fundraising - Having a vision with clearly articulated desired conditions and a detailed plan for achieving them has provided a strong basis for fundraising. The budget for the native fish program in Yellowstone is highly diverse and is used to implement a wide range of conservation actions each year. The program is primarily supported by the NPS, other federal agencies, private donations to the Yellowstone Park Foundation (now Yellowstone Forever), and competitive grant awards. Formal partnerships enhance fundraising potential even further. For example, significant funding to support a large, multi-year research initiative on Yellowstone Lake has been acquired by the Yellowstone Lake Workgroup. This funding supports critical research aimed at understanding lake trout movements and spawning locations. Without partner support and fundraising, important studies like this could not take place.
Actions - The activities necessary to preserve and restore native fish varies by species and drainages across the park. Because genetically pure westslope cutthroat trout and Arctic grayling are mostly gone from park waters, activities within the Gallatin and Madison river drainages include creating barriers and isolating headwater refuges; removing non-native and hybrid fish using piscicides (fish toxins); and reintroducing native species as eggs, juveniles, and/or adults from genetically- unaltered or other pure sources from within and outside YNP. Yellowstone cutthroat trout still persist, and all life history forms (large-river migratory, stream-resident, lake-dwelling) are represented in several river systems across the park. However, because they occur in populations mixed with non-natives or hybrids, the actions taken to conserve Yellowstone cutthroat trout focus on selective removal of rainbow trout and hybrids via electrofishing and angling from these waters. On Yellowstone Lake, substantial conservation actions are being taken to restore cutthroat trout. During a six-month field season (May-October), several crews operating large boats set and retrieve miles of net to catch and kill non-native lake trout. In addition, biologists are developing new, alternative methods to suppress lake trout. These actions include electroshocking, suction-dredging, placement of lake trout carcasses, and/or use of rotenone to kill embryos on spawning areas.
Assessment - Long-term monitoring and statistical population modeling are conducted to determine if conservation actions are positively influencing native fish as desired. Independent review of native fish conservation actions and data assessment are provided by technical specialists from state and federal agencies and universities. For the lake trout suppression program specifically, there is a standing panel of scientists that meets annually to provide a critical review (Gresswell et al. 2015). Questions to be addressed through research are also identified. These research needs are met through collaborations with several university and federal (e.g., U.S. Geological Survey) scientists and graduate assistants.
Following an adaptive management approach, feedback obtained during reviews and assessments are used to adjust conservation actions to progress towards desired conditions. This approach is used because of the varied environments and stressors impacting native fish across the park, and the fact that some uncertainty exists in the possible response by native fish following management actions. For example, although initial science indicates lake trout expansion in Yellowstone Lake could be curtailed, it is not known precisely how many years high levels of suppression need to be maintained or if the effort could eventually be reduced without resulting in a lake trout resurgence. Similarly, the rate of native cutthroat trout recovery after the population is released from overriding lake trout impacts is also uncertain. Because of these and other uncertainties, performance metrics are closely monitored to track system responses to lake trout suppression; and the results are used to make adaptations and adjust management actions each year.
Moving Forward with Measurable ObjectivesSeveral recent, significant advancements have been made towards achieving desired conditions for native fish in Yellowstone. However, actions need to be sustained and continued if goals of the Native Fish Conservation Plan are to be met. These efforts would include innovative actions to remove threats and stressors (e.g., non-native fish such as lake trout), thereby creating refuges for native fish as climate change alters aquatic habitats across their respective historic ranges in the future. Measurable objectives are the guiding benchmarks to determine if the purpose and need for an action are being met. At present, the technology does not exist to fully eradicate lake trout from Yellowstone Lake or to completely remove all non-native fish from large, complex river systems. Given these constraints, the measurable objectives for the Yellowstone Lake ecosystem are to:
1. increase large-scale suppression of lake trout so more than half are removed annually, driving the population into decline;
2. maintain surface water access for spawning cutthroat trout in spawning tributaries; and
3. recover cutthroat trout to abundances observed during the early stages of lake trout invasion.
Once the lake trout population has been reduced and spawning tributary connections have been maintained, it is anticipated that an additional 10 years (20 years following plan implementation) may be required for cutthroat trout recovery. The cumulative result of multiple projects would be used to meet the following measureable objectives for streams, rivers, and other lakes:
4. preserve and/or restore Yellowstone cutthroat trout to maintain their current spatial extent in streams (3,300 km [2050 mi.]);
5. restore westslope cutthroat trout until they occupy at least 200 km (124 mi.); and
6. restore fluvial (i.e., stream-dwelling) Arctic grayling until they occupy at least 200 km (124 mi.).
We intend to work within a few project areas each year, with the cumulative results of multiple projects meeting Objectives 4-6 within 20 years.
A healthy ecosystem requires sustainable communities of both terrestrial and aquatic organisms. Park managers have documented the repercussions of historical, non-native fish introductions, including the resulting loss of native fish populations and cascading effects on the environment. In addition, over the past two decades, it has become apparent that these changes were not static. In fact, real-time, present-day losses were occurring to premier, native cutthroat trout populations and fisheries recognized by anglers world-wide. The technology to preserve and restore native fish has greatly advanced in recent years, and YNP is among those actively developing and using these new methods. Park managers, guided by a large body of science and with support by a multitude of external partners, have implemented an aggressive native fish conservation program, which will ensure the persistence of native fish and the ecosystems they support far into the foreseeable future.
Literature CitedFranke, M. A. 1997. A grand experiment. The tide turns in the 1950s: Part II. Yellowstone Science 5:8-13.
Gresswell, R.E., C.S. Guy, M.J. Hansen, M.L. Jones, J.E. Marsden, P.J. Martinez, and J.M. Syslo. 2015. Lake trout suppression in Yellowstone Lake: science review panel. Interim Scientific Assessment, 2014 Performance Year Final Report. YCR-2015-04. National Park Service, Yellowstone Center for Resources, Yellowstone National Park, Wyoming, USA.
Jordan, D.S. 1891. A reconnaissance of streams and lakes in Yellowstone National Park, Wyoming in the interest of the U.S. Fish Commission. Bulletin of the U.S. Fish Commission 9:41- 63.
Kaeding, L.R., G.D. Boltz, and D.G. Carty. 1996. Lake trout discovered in Yellowstone Lake threaten native cutthroat trout. Fisheries 21:16–20.
Koel, T.M., P.E. Bigelow, P.D. Doepke, B.D. Ertel, and D.L. Mahony. 2005. Non-native lake trout result in Yellowstone cutthroat trout decline and impacts to bears and anglers. Fisheries 30:10-19.
Koel, T.M., J.L. Arnold, P.E. Bigelow, and M.E. Ruhl. 2010. Native fish conservation plan. Environmental assessment, December 16, 2010. National Park Service, U.S. Department of the Interior, Yellowstone National Park, Wyoming, USA. http:// parkplanning.nps.gov/document. cfm?parkID=111&projectID= 30504&documentID=37967.
Madsen, D.H. 1937. Protection of native fishes in the National Parks. Transactions of the American Fisheries Society 66:395- 397.
Syslo, J.M. 2015. Dynamics of Yellowstone cutthroat trout and lake trout in the Yellowstone Lake ecosystem: a case study for the ecology and management of non-native fishes. Dissertation. Montana State University, Bozeman, Montana, USA.
Tronstad, L.M., R.O. Hall, Jr., T.M. Koel, and K.G. Gerow. 2010. Introduced lake trout produced a four-level trophic cascade in Yellowstone Lake. Transactions of the American Fisheries Society 139:1536-1550.
Varley, J.D., and P. Schullery. 1998. Yellowstone fishes: ecology, history, and angling in the park. Stackpole Books, Mechanicsburg, Pennsylvania, USA.
White, P.J., with R.A. Garrott, editor. 2016. Can’t chew the leather anymore: musings on wildlife conservation in Yellowstone by a broken-down biologist. Yellowstone Association, Gardiner, Montana, USA.
Todd Koel has served as leader of the Native Fish Conservation Program at Yellowstone National Park since 2001. Koel holds affiliate and graduate faculty status at Montana State University and University of Wyoming. A native of northern Minnesota, Koel received his Ph.D. in Zoology from North Dakota State University in 1997. After teaching at colleges in Minnesota and North Dakota, he served as Riverine Fish Ecologist and Interim Field Station Director for the Illinois Natural History Survey at Havana. He later worked for the Minnesota Department of Natural Resources on a resource monitoring program for the Upper Mississippi River System. When not working on the conservation of cutthroat trout, Koel spends most of his time with his four young boys and two horses roaming the backcountry of the Greater Yellowstone Ecosystem.