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  5. Susceptibility of Rio Grande Cutthroat Trout to Displacement by Non-Native Brown Trout and Implications for Future Management

Susceptibility of Rio Grande Cutthroat Trout to Displacement by Non-Native Brown Trout and Implications for Future Management

Susceptibility of Rio Grande Cutthroat Trout to Displacement by Non-Native Brown Trout: Implications for Future Management and Persistence of the Most Southern Subspecies of Inland Cutthroat Trout in the Face of a Changing Climate
Principal Investigator
Colleen Caldwell

Dates

Start Date
2018-06-26
Acquisition
2019-09-30
Release Date
2018

Summary

The Rio Grande cutthroat trout is New Mexico’s state fish; but habitat loss and non-native trout invasions threaten the persistence of this fish throughout the remaining 12% of its historic range. Stakeholders, including state agencies, federal agencies, Tribal nations, Pueblos, and private groups are particularly concerned about the impact that non-native brown trout have on native cutthroat trout. This project will be the first to demonstrate how non-native brown trout negatively affect Rio Grande cutthroat trout populations. The project has two primary objectives: 1) compare the health and characteristics of native Rio Grande Cutthroat Trout in areas both with and without invasive brown trout in cold and warm streams; and 2) determine [...]

Child Items (3)

Contacts

Principal Investigator :
Colleen Caldwell
Co-Investigator :
Brock Huntsman, Abigail Lynch, Lauren Flynn
Funding Agency :
South Central CASC
Cooperator/Partner :
Bryan Bakevich, Kirk Patten, Yvette Paroz, James Gruhala
CMS Group :
Climate Adaptation Science Centers (CASC) Program

Attached Files

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RioGrandeCutthroatTrout_USFWS.jpg
“Rio Grande Cutthroat Trout, USFWS - Credit” 		thumbnail 90.32 KB image/jpeg
RioGrande_USFWS_crop.jpg
“Rio Grande; Credit: USFWS” 		thumbnail 129.2 KB image/jpeg

Purpose

Rio Grande Cutthroat Trout is New Mexico’s state fish; but habitat loss and non-native trout invasions threaten the persistence of the remaining populations throughout the remaining 12% of its historic range. This project will address concerns of a consortium of stakeholders that include two state agencies, eight federal agencies, two Tribal nations, three Pueblos, and three private groups. Thus, this diverse team of stakeholders want to proactively manage threats to RGCT persistence, including global change and non-native species. These stakeholders are gravely concerned about the impact that non-native Brown Trout have on native cutthroat trout. Brown Trout are the most widespread of invasive trout species in the world. Populations of cutthroat trout in the Southwest experience a broader range of temperatures that are also suitable for Brown Trout; thus, the continued invasion by Brown Trout in southern latitudes may have a more profound effect than in cutthroat trout from more northern latitudes. Understanding the relationship between temperature and non-native species invasion for this southernmost subspecies of cutthroat trout will benefit all cutthroat subspecies into the future as northern latitudes endure the effects of a warming climate and continued non-native trout invasions. This project will be the first to demonstrate how non-native Brown Trout negatively affect RGCT populations. To do this, we will compare annual changes in production of RGCT populations and relate these changes to the diets of RGCT in the presence and absence of Brown Trout across a temperature continuum. The rate at which a population collectively accumulates biomass is critical to population persistence because more biomass translates to increased reproductive capacity, increased competitive ability, and ultimately increased survival. Our results will be invaluable for managers to balance RGCT restoration efforts while maintaining popular sportfish destinations (albeit Brown Trout), by identifying and focusing restoration efforts on streams with the greatest potential to support RGCT.

Project Extension

parts
typeTechnical Summary
valueThere are three universal ecological responses to global warming by coldwater fishes. The first is a shift in species distributions to more northern latitudes and higher altitudes. The second is the shift in phenology when the timing of life history stages such as earlier emergence of larvae from redds results in a mismatch in the availability of food. More recently, a third ecological response associated with a warming climate has been observed among coldwater fishes where size scaling properties of increased metabolism with increased temperature creates a metabolic trap that results in a reduction in body size. Collectively, these ecological responses will have significant implications on the productivity of RGCT as isolation (response 1) and elevated metabolic demand (response 3) will increase energetic needs that cannot be maintained by available forage resources. No doubt, these stressors to Rio Grande Cutthroat Trout productivity, the most southern subspecies of Cutthroat Trout, will be exacerbated by the presence of non-native Brown Trout. Recent research suggests that when RGCT and Brown Trout co-occur, Brown Trout limit RGCT access to the needed forage and refugia. Thus, we predict that the productivity of RGCT will be further limited by Brown Trout when both species co-occur in warmer streams. Brown Trout typically inhabit warmer streams than native Cutthroat Trout, but have invaded Cutthroat Trout streams throughout the intermountain west. Thus, managers are gravely concerned that a warming climate will facilitate increase distribution of Brown Trout and eventually outcompete RGCT for limited resources. As such, we have been charged by the RGCT Conservation Team (a stakeholder advisory group that has a unified vision to conserve and enhance RGCT) to assess the effects that Brown Trout have on the productivity of RGCT. Objective 1: Characterize growth rates, biomass, and rates of secondary production for RGCT in allopatry and sympatry with Brown Trout in cold and warm streams. Mark-recapture research by collaborators observed a non-linear relationship between rates of secondary production and stream temperature for seven RGCT populations. These results suggest secondary production (product of fish biomass and growth rate) is limited only by metabolism in cooler streams and availability of foraging resources in warmer streams. However, a breached barrier by Brown Trout in a colder stream coincided with substantially lower rates of RGCT production than all other streams, even though RGCT should be better competitors with Brown Trout at colder temperatures. Therefore, we predict Brown Trout will be stronger competitors in warmer than colder streams and that the presence of Brown Trout in sympatry with RGCT will magnify losses in RGCT productivity. To test our prediction, we have selected four streams where RGCT populations exist alone (in allopatry) across a temperature continuum and four streams where RGCT and Brown Trout populations are found together (in sympatry) across a temperature continuum. We will test for the significance of interactions between temperature and Brown Trout that affect growth, biomass, and production of RGCT. Objective 2: Determine if competition for food resources is the mechanism that limits rates of secondary production in RGCT populations. Research by collaborators demonstrated that Brown Trout significantly affected the foraging ecology of RGCT. When in sympatry with Brown Trout, RGCT consumed higher amounts of low quality terrestrial prey items than RGCT from all other streams. This provides the causal mechanism by which Brown Trout displace RGCT, as poor forage quality will significantly reduce growth and production of coldwater salmonids. Thus, we predict that in warmer streams, this effect will be magnified since greater forage will be needed to match the metabolic demand of both salmonids. Thus, we will combine mark-recapture sampling for production estimates (Objective 1) with macroinvertebrate availability and diet sampling to develop a quantitative energy flow web for RGCT when in allopatry and sympatry with Brown Trout across our temperature treatments. Both Objectives 1 and 2 are essential to stakeholders needs, as RGCT displacement by Brown Trout is a significant management concern. Stakeholders have invested needed resources to manage risks of invasion to RGCT populations through unpopular chemical removal and construction of expensive barriers only to have the barriers fail. Thus, our research will allow for more informed decisions of which RGCT populations stakeholders should focus their efforts and resources to conserve that have the greatest potential for productivity now and into the future.
projectStatusCompleted

Budget Extension

annualBudgets
year2018
totalFunds49473.0
parts
typeAward Type
valueCOA
totalFunds49473.0

Rio Grande; Credit: USFWS
Rio Grande; Credit: USFWS

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Type Scheme Key
RegistrationUUID NCCWSC 33e197db-7489-4457-bc8c-49b7a4a6ee91
StampID NCCWSC SC18-CC1305

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