Cutthroat conservation

I. Background

  1. Colorado River cutthroat trout (CRCT) are 1 of 4 subspecies of native trout inhabiting state waters [1, 2].

  2. The other 3 are Greenback (or Bear Creek), Rio Grande, and San Juan; Yellowfin cutthroat are believed extinct [2, 3].

  3. At least 24 of 42 perennial streams in the Dolores River basin are known to host cutthroat trout [4].

  4. Fin sampling is an initial part of locating cutthroat trout with historic characteristics, shown in the photo below.

  5. A trout is held briefly out of water, a very small portion of its tail fin snipped, and then it is returned to the stream.

    Cutthroat | Decision | Nominee

Fin sampling at Morrison Creek
FinCrop

A. Lineages

  1. At least 6 of the cutthroat trout streams have predominantly green lineage CRCT, based on DNA analysis [5].​

  2. Green is one of 2 lineages (subspecies) of CRCT, along with blue [3, 6].

  3. From Little Taylor in the Dolores basin, CRCT were 95% green and 1% blue lineage, and 3% rainbow [6].

  4. Green and blue lineages "are both widely distributed today...on both slopes of the Continental Divide" [3].

  5. These lineages are based on museum samples collected after active stocking began, around 1855 [3].

  6. Consequently, the "native distribution and taxonomy" of green and blue lineage CRCT remain uncertain [3].

  7. Green lineage "appears native to the Colorado and Gunnison rivers," and possibly the Arkansas basin [3].

  8. "Human activities have muddled [the] native distribution patterns" of CRCT [6].

  9. More than 750 million brook, rainbow, and cutthroat trout were stocked in Colorado in 1885-1953 [3].

  10. A result has been "confusion regarding the conservation status of rare [cutthroat] forms" [6].

  11. As well, rainbow trout, which are non-native, readily hybridize with cutthroat trout [6, 7].

  12. Brook and brown trout, also non-native, tend to replace cutthroat by outcompeting for habitat [3, 6].

B. Threats

  1. The spread of non-native trout may be the greatest threat to the continued existence of CRCT populations [7, 8].

  2. The consequences are diminished pure CRCT stock and declining cutthroat populations, in general.

  3. In addition, trout are stressed by rising water temperatures and stream dewatering due to climate change.

  4. "The diversity and distribution of cutthroat trout have changed dramatically over the last 150 years" [3].

  5. "Preservation of the native cutthroat trout genome" has the attention of wildlife agencies in multiple states [9].

  6. Whether green lineage proves to be part of the CRCT line or another cutthroat subspecies... [10]

  7. It is "critical to seek to preserve the substantial diversity contained in this lineage" [10].

II. Considerations

  1. CRCT conservation agreement and strategy were developed by agencies from Colorado, Wyoming, and Utah [11, 12].

  2. The conservation strategy's purpose is "to stabilize or enhance its populations, and to maintain its ecosystems" [12].

  3. CRCT is designated as a special status species by Colorado and as a sensitive species by the U.S. Forest Service [12].

A. Core conservation populations

  1. The strategy recognizes a CRCT core conservation population as having greater than 99% purity [9, 12].

  2. That is, it has "no detectible introgression" and is "phenotypically true" [8]; it is an "unaltered population" [12].

  3. Such a population "represents the historic genome of the native cutthroat trout" [9].

  4. Its application in the strategy is "to facilitate long term persistence...in a genetically pure condition" [9].

  5. Note that a population is a "waterbody" hosting cutthroat trout; populations are "geographically distinct" [9].

  6. A population is "reproducing and recruiting as a geographically distinct group" [12].

  7. Development of metapopulations can enhance long-term persistence of core conservation populations [9].

  8. Metapopulations are "geographically distinct" but "genetically interconnected" by natural trout movement [9].

  9. The desired result can be enhancement (by gene flow) of diversity (allelic richness) in the historic genome [13].​

  10. Core populations can provide gametes to introduce through "transplants and brood stock development" [9, 12].

B. Conservation populations

  1. In the strategy, conservation populations have at least 90% purity, with 10% or less introgression [9, 12].

  2. Introgression is reproduction between native cutthroat and other cutthroat subspecies or salmonid species.

  3. Their application would be for preservation of "unique genetic, ecological, and/or behavioral characteristics"...

  4. Within specific populations and geographic settings; or for preservation of the historic genome [9].
  5. A unique genetic or ecological attribute could be large size or adaption to extreme environmental conditions [9].
  6. They may contribute to maintaining sport fishing populations for meeting public recreational demand [9].

  7. That is, despite slight genetic introgression, they still retain phenotype (physical identities) valued in sport fishing.

C. Additionally

  1. The Molecular Model has been found more successful than the Geographic Model for classifying cutthroat [3, 6].

  2. Acceptance of small amounts of hybrid influence may be needed "to preserve a larger...CRCT diversity" [12].

III. Application

  1. Effective CRCT management has both conservation and recreation (sport fishery) elements [9].

  2. It may include restrictions in stocking, passage barriers, disease control, and limits in harvesting, for instance [12].

  3. Decision framework offers an example of thinking about CRCT and wild trout habitat preservation and management.

  4. The Nominee streams page shows an example of visualizing application of a CRCT conservation strategy.

  5. Colorado Parks and Wildlife (CPW) is committed to protecting and managing cutthroat populations [2, 5].

  6. CPW uses DNA analysis to identify population characteristics [5].

  7. Analyses are conducted on very small portions snipped from cutthroat tail fins, indicated in the photo above.

  8. Dolores River Anglers (DRA) members of Trout Unlimited (TU) have assisted with fin sampling, as shown above.

References

  1. https://cpw.state.co.us/cutthroat-trout and https://cpw.state.co.us/learn/Pages/ResearchColoradoRiverCutthroatTrout.aspx

  2. “Colorado Parks and Wildlife Announces Discovery of Unique Cutthroat Trout in Southwest Colorado,” CPW News Release, Department of Natural Resources, Colorado Parks and Wildlife, 4 Sep 2018; https://cpw.state.co.us/aboutus/Pages/News-Release-Details.aspx?NewsID=6676

  3. Metcalf, J. L., S. Love Stowell, C. M. Kennedy,  K. B. Rogers, D. McDonald, J. Epp, K. Keepers, A. Cooper, J. J. Austin, and A. P. Martin, Historical Stocking Data and 19th Century DNA Reveal Human-Induced Changes to Native Diversity and Distribution of Cutthroat Trout," Molecular Ecology, DOI: 10.1111/mec.12028, 2012.

  4. "Climate Change and the Upper Dolores Watershed: A Coldwater-Fisheries Adaptive Management Framework," Prepared for Dolores River Anglers Chapter of Trout Unlimited, 2017.

  5. White, J., “Status of Colorado Cutthroat Trout in the Upper Dolores River Basin,” Presented at Dolores River Trout Unlimited Meeting, January 14, 2019.

  6. Bestgen, K. R., K. B. Rogers, R. Granger, "Distinct Phenotypes of Native Cutthroat Trout Emerge under a Molecular Model of Lineage Distributions," Transactions of the American Fisheries Society, vol. 148, pp. 442–463, DOI: 10.1002/tafs.10145, 2019.

  7. Behnke, R. J., "Native trout of western North America," American Fisheries Society, Monograph 6, 1992.

  8. Young, M. K., R. N. Schmal, T. W. Kohley, and V. G. Leonard, “Conservation Status of Colorado River Cutthroat Trout,” U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station, Ft. Collins, CO, General Technical Report RM-GTR-249, 1996.

  9. "Cutthroat Trout Management: A Position Paper, Genetic Considerations Associated with Cutthroat Trout Management," Developed by: Colorado Division of Wildlife; Idaho Department of Fish and Game; Montana Fish, Wildlife and Parks; Nevada Division of Wildlife; New Mexico Game and Fish; Utah Division of Wildlife Resources; Wyoming Game and Fish Department, 2000.

  10. Rogers, K. B., K. R. Bestgen, and J. Epp, "Using Genetic Diversity to Inform Conservation Efforts for Native Cutthroat Trout of the Southern Rocky Mountains," Wild Trout Symposium XI, Looking Back and Moving Forward, 281--Session 5: Status and Management of Native Salmonids, 2014.

  11. "Conservation Agreement, Colorado River Cutthroat Trout (Oncorhynchus clarkii pleuriticus) in the States of Colorado, Wyoming, and Utah," Colorado Division of Wildlife, Fort Collins, 2006.

  12. "Conservation Strategy for Colorado River Cutthroat Trout (Oncorhynchus clarkii pleuriticus) in the States of Colorado, Wyoming, and Utah," Prepared by CRCT Coordination Team, Colorado Division of Wildlife, Ft. Collins, 2006.

  13. Carim, K. J., L. A. Eby, C. A. Barfoot, and M. C. Boyer, "Consistent Loss of Genetic Diversity in Isolated Cutthroat Populations Independent of Habitat Size and Quality, Conservation Genetics, v. 17, pp. 1363-1376, DOI 10.1007/s10592-016-0867-9, 2016.

    Cutthroat | Decision | Nominee