Status and Conservation of Yellowstone Cutthroat Trout in the Greater Yellowstone Area

from: Yellowstone Science 25 (1)

by Robert Al-Chokhachy, Bradley B. Shepard, Jason C. Burckhardt, Scott Opitz, Dan Garren, Todd M. Koel, & M. Lee Nelson

Yellowstone cutthroat trout are native to the Greater Yellowstone Ecosystem (GYE) and surrounding drainages, including the Yellowstone River, Snake River, and Two Ocean Pass that facilitate connectivity between these drainages (Behnke and Tomelleri 2002; figure 1). Despite some differences in physical appearance between fine-spotted cutthroat trout, typically found in the Snake River, and “largespot,” found across much of the range, there has been no evidence of genetic distinction between these two groups of Yellowstone cutthroat trout (Novak et al. 2004).

Yellowstone cutthroat trout live in a variety of habitats, including small headwater streams, large rivers (e.g., Yellowstone and South Fork of the Snake rivers), and lakes, each demonstrating multiple life-history forms (Gresswell 2011). These trout are a key component of native communities as a food resource for several species (see “Birds and Mammals that Consume Yellowstone Cutthroat Trout,” this issue). Indeed, changes in Yellowstone cutthroat trout abundance can have cascading effects on ecosystems (see “Non-native Lake Trout Induce Cascading Changes in the Yellowstone Lake Ecosystem,” this issue). Yellowstone cutthroat trout also embody an important cultural and economic role through angling for many communities in the area (Gresswell and Liss 1995).

There have been significant declines in Yellowstone cutthroat trout distribution (figure 1) and abundance, with only 43% of their historic range currently occupied (Endicott et al. 2016). Losses of Yellowstone cutthroat trout have largely been attributed to habitat destruction and fragmentation, non-native species, and overharvest (Gresswell 2011). Only 23% of the current distribution of Yellowstone cutthroat trout is genetically unaltered (i.e., pure), with losses of genetic integrity largely due to hybridization with non-native rainbow trout (Campbell et al. 2002). However, recent assessments indicate the distribution of Yellowstone cutthroat trout has remained relatively stable over the past decade (Endicott et al. 2016). Coordinated efforts of fisheries managers through the Multistate Interagency Yellowstone Cutthroat Trout Conservation Work Group (May et al. 2007) are likely responsible for stemming declines in distribution observed during earlier decades.

Threats and Conservation Actions to Combat Threats

The severity of threats to populations of Yellowstone cutthroat trout have changed recently, and these changes are likely to continue into the future. Overharvest has been greatly reduced through angling regulations and changes in angler behavior (Cooke and Schramm 2007). As a result, current threats are primarily related to non-native species, habitat limitations, and climate change.

Non-native species—These are one of the greatest threats across the current range of Yellowstone cutthroat trout (Gresswell 2011). Species including rainbow trout, brook trout, and brown trout were extensively introduced as sport fish. While populations of some non-native species are socioeconomically important resources to many communities, they can threaten Yellowstone cutthroat trout populations through predation, competition, and hybridization (Campbell et al. 2002, Peterson et al. 2004, Seiler and Keeley 2007). Recent studies indicate the distribution and abundance of non-native species are increasing through time (Meyer et al. 2014). Streams accessible to these non-native species, even in some of the most pristine locations like the Lamar River in Yellowstone National Park, are being invaded by non-native species such as rainbow trout. Changes in non-native fish distributions and the effects of these non-native species on Yellowstone cutthroat trout will likely be exacerbated by climate change (Al-Chokhachy et al. 2013).

Fisheries managers have implemented a variety of conservation tools across the range of Yellowstone cutthroat trout to combat non-native species and enhance the persistence of existing populations. Tools include using fish toxins (piscicides) and mechanical methods (e.g., electrofishing) to remove non-native species in streams, erecting barriers to prevent invasions by non-natives, creating angler incentives to harvest non-natives, altering releases at hydropower dams to limit non-native spawning recruitment, and implementing intensive netting programs to reduce populations of lake trout. For example, Idaho Fish and Game recently implemented an incentive program to encourage anglers to harvest non-native rainbow trout in order to reduce their abundance in the South Fork of the Snake River. Similarly, Yellowstone National Park recently altered angling regulations to align with native fish conservation goals. Other approaches, such as the use of barriers that isolate populations from non-natives but also fragment cutthroat populations, represent a necessary paradigm in fisheries (Peterson et al. 2008). Often such programs are socially challenging and costly, yet may be necessary due to recent invasions by non-native species and their effects on Yellowstone cutthroat trout (Kruse et al. 2000).

Habitat—Degradation and fragmentation of habitat continue to be factors limiting Yellowstone cutthroat trout populations in some areas. Degradation has occurred to varying extents from land use, habitat alteration, and water diversions. Over the past 20 years, a substantial amount of habitat has been restored by state and federal agencies and non-governmental organizations (e.g., Friends of the Teton River, Henry’s Fork Foundation, Trout Unlimited; Williams et al. 2015). Projects that improve fish passage, limit entrainment into irrigation systems, prevent invasion of non-native species, and restore stream channels and riparian habitat have been implemented across the range of Yellowstone cutthroat trout (figure 2). Despite such efforts, there continue to be abundant opportunities for additional restoration projects in areas currently occupied by Yellowstone cutthroat trout and in historically occupied areas where reintroductions may be feasible.

Climate change—Recent and future changes in climatic conditions have and are expected to substantially alter aquatic communities in the GYE and surrounding areas (Shepard et al. 2016). Cutthroat trout have relatively narrow thermal tolerances (Bear et al. 2007), and migration timing and life-history expressions are strongly tied to thermal and hydrologic regimes (DeRito et al. 2010). Warming summer temperatures coupled with changes in the magnitude and timing of precipitation and snowmelt runoff are likely to create more stressful summer conditions for Yellowstone cutthroat trout in some areas (Uthe et al., in review). As stream temperatures warm, the amount of thermally suitable habitat for Yellowstone cutthroat trout may be reduced considerably in some populations (Al-Chokhachy et al. 2013, Isaak et al. 2015). Lake-dwelling populations will also be affected by climate change because they rely on adequate connectivity to tributary streams (Kaeding 2010). In addition to the direct effects of changing thermal regimes, Yellowstone cutthroat trout are likely to become increasingly exposed to diseases in streams where temperatures warm dramatically (Koel et al. 2006) and suffer increased mortality from catch-and-release angling (Cooke and Schramm 2007). Most fish managers in the region restrict opportunities for angling when water temperatures reach critical levels, and these restrictions will likely become more frequent as the climate warms. Such restrictions may affect visitation to the Yellowstone area because angling is often an important component of tourism.

Future Conservation of Yellowstone Cutthroat Trout

Significant efforts are being made to maintain and enhance the existing distribution of Yellowstone cutthroat trout and stem the tide of historic losses. Fortunately, large networks of Yellowstone cutthroat trout populations still exist, particularly within the Yellowstone, the Upper Snake, and Lower Snake rivers (Endicott et al. 2016). The vast expanses of public land at relatively high elevations, including Yellowstone and Grand Teton national parks, can and will likely continue to support cold water habitats that make up the core areas of the Yellowstone cutthroat trout. Populations outside these large lake and river networks vary in size. While populations occupying larger, connected stream networks are likely more resilient (Morita et al. 2009), small populations of Yellowstone cutthroat trout also can have high resiliency (e.g., Peterson et al. 2014). Furthermore, geographically distinct populations (e.g., Camas Creek drainage, lower Bighorn drainage, and the Snake River near the Idaho/Utah border; Haak et al. 2010) are likely to represent areas of key genetic diversity that facilitate the long-term persistence of the species.

The extent and severity of current (e.g., non-natives) and future (e.g., climate change) threats to Yellowstone cutthroat trout populations suggest it will become increasingly important to address these concerns and secure populations. The relatively broad distribution of Yellowstone cutthroat trout suggests the importance in developing effective and coordinated conservation strategies (Williams et al. 2015), particularly as resource constraints often predicate the need to prioritize conservation actions (Lynch and Taylor 2010). With respect to climate change, this may involve identifying habitats that are most resilient to climatic shifts, both within the current distribution and where Yellowstone cutthroat trout were historically located to target population reintroductions. For example, populations with considerable groundwater inputs or those with access to deep, thermally stratified lakes (e.g., Yellowstone and Jackson lakes) are likely to be particularly resilient to climatic shifts.

Continued threats by non-native species will require expanding the tools to cost-effectively reduce or eliminate their threat to important Yellowstone cutthroat trout populations. We need to increase public support for dealing with these threats through improved communication with the public of how non-native species and illegal introductions threaten populations of Yellowstone cutthroat trout. Concomitantly, it will be important to consider novel approaches to control non-native populations, particularly given the high costs and efforts often needed to successfully reduce and/or remove non-native species.

Merging information regarding climatic resilience with existing non-native threats to populations can provide an overall framework for considering the urgency of conservation and management actions. For example, restoring habitat or removing a non-native species in an area with high climatic resilience may be given a higher priority for funding conservation actions than other areas that may be more sensitive to future climatic changes (Lynch and Taylor 2010). Decisions to implement particular conservation actions might be made through a hierarchical framework that considers potential conservation opportunities at range-wide, regional, and local scales, in terms of financial support and the ecological importance of specific populations. Within this framework, coordinating efforts across public and private entities to conserve and restore Yellowstone cutthroat trout populations will become increasingly important in the future, as both our human footprint and conservation needs grow.

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Robert Al-Chokhachy is a Research Fisheries Biologist with the USGS Northern Rocky Mountain Science Center in Bozeman, MT. Robert received a PhD in aquatic ecology from Utah State University in 2006 and conducted postdoctoral research related to threatened and endangered salmonids before joining the USGS in 2010. His current research aims to provide information for effective management and conservation of aquatic ecosystems. Since moving to Bozeman, a large component of his research has focused on the ecology, management, and conservation of Yellowstone cutthroat trout, particularly in the context of climate change.

 

Figure 1.  The historic and current distribution of Yellowstone cutthroat trout within the Greater Yellowstone Are in Montana, Wyoming, Idaho, Utah, and Nevada.