Nominee streams

  B. Populations​

1. In those strategies, a core conservation population has greater than 99% historic genome characteristics [1, 2].

2. A conservation population is at least 90% pure, with no more than 10% genetic material from other sources [1, 2].

3. So, the initial item in the flow chart: Is a core conservation or conservation population present in the stream?

4. Or, alternatively, is the stream a possible host for such populations?

5. Natural or installed barriers to fish passage in a stream may be part of keeping native and wild trout separated.

6. As isolated populations, cutthroat can be monitored for indications of viability, inbreeding, and genetic drift.

7. Problems are most likely and pronounced in small populations; genetic drift is an occurrence of chance [3].

8. Researchers have shown a "consistent loss of genetic diversity through time in isolated populations" [3, 4].

9. Risks from barriers and non-native invasion are not well understood; management efforts may be experimental [4].

  C. Size​

1. About 6 mi of "suitable steam habitat" may be needed to overcome isolation and "maintain genetic diversity" [4].

2. For context, Dolores streams are 2.4-19 mi long; 13 are >6 mi; the upper Dolores (above McPhee Res.) is 60 mi long.

3. Isolated cutthroat had a 50% chance of establishing reproducing populations with >5.7 sq mi drainage area [4, 5].

4. Translocated population success in the 27 Colorado and New Mexico streams increased to 90% with >13 sq mi [5].

5. Again, for context, the drainage areas of Dolores streams are 1.2-46 sq mi; 5 are >13 sq mi; 13 are >6 sq mi.

  D. Metapopulations

1. Metapopulations are "geographically distinct" but "genetically interconnected" by natural trout movement [1, 2].

2. Development of metapopulations may bring more variety in spawning, resulting in greater genetic diversity.

  E. Water quality​

1. Grazing and timbering can bring streambed sedimentation, which can diminish food supply and reproduction [6, 7].

2. Nutrients and waste solids in runoff from pastures also can result in streambed coverings, including algae growth.

3. Some Dolores watersheds have grazing, as permitted by the Forest Service in range allotments and pastures.

4. The Dolores basin also has watersheds with no grazing, which may be more attractive for dependable water quality.

5. That is, favorable streams for conservation, where possible, have minimal exposure to potential loss of water quality.

6. Possible, too, is monitoring and maintenance of habitat water quality in watersheds with grazing and timbering.

  F. Example​

1. Little Taylor, having water that met aquatic standards and hosting CRCT, has Colorado Outstanding Waters status.

2. The taxonomy of tissue from trout taken from Little Taylor showed 95% green lineage CRCT [8].

3. Reproduced with enough individuals, such results would indicate a conservation population, that is, >90% pure [1].

4. Little Taylor is small, however: stream length, 4.8 mi; drainage area, 3.0 sq mi; and mean annual flow, 2.7 cfs.

5. These are below possible minimums of 6 mi length and 13 sq mi area for long-term, reproducing populations [4, 5].

6. If the stream became stressed, by drought, for example, a CRCT population could be severely damaged or lost.

7. In fact, the tributary into which it flows, Taylor, completely dewatered in fall 2020, as seen in slide 10, Drought flows.

8. A Little Taylor population could be a good example of value, perhaps urgency, for seeding larger, more stable habitat.

  G. Sorting​

1. Larger-flow streams have larger volumes for habitat, with the most water to lose from drought before habitat is lost.

2. High maximum elevations and large drainage areas are part of resilience to dewatering.

3. With high elevations, snowmelt has greater contribution to recharge of stream baseflow than lower-elevation streams.

4. Large drainage areas mean more capture of precipitation for immediate in-channel flow and recharge of baseflow.

5. See the Dolores River basin's streams sorted by flow, mean annual and mean July-August, highest to lowest.

6. Little Taylor, mentioned above, is 37th and 39th out of the 42 streams in mean annual and mean July-August flow.

7. See also the streams sorted by maximum elevation and drainage area, combined, highest to lowest.

8. As well, those streams sorted by maximum elevation, drainage area, and stream length, combined, highest to lowest.

9. Little Taylor is 35th out of the 42 streams in that sorting.

10. Interestingly, but not necessarily surprisingly, the sorts identify the same top 10 streams, with one exception.

11. Attractive streams not having conservation populations may be candidate hosts for transplants.

  H. Application​

1. Upper portions of watersheds may be attractive nominee s, away from land-use activities at lower elevations.

2. For example, an upper 6 mi [4] or more might host protected populations at Stoner, 19 mi in length, and Fish, 15 mi.

3. Large-flow Bear, 16 mi in length, has no water withdrawal or grazing at upper or lower elevations...

4. And might be an attractive nominee for a cutthroat conservation population higher and refuge for wild trout lower.

5. Streams enabling metapopulations with exchange of trout logically could be highly attractive as nominees...

6. But, absent that, streams otherwise may be opportune, as represented by the dashed line above at steps 3 and 4.

7. For instance, streams may be attractive because they have enhanced baseflow from upstream ponds...

8. For example, as from a man-made impoundment at Barlow and beaver dams at Stoner, Scotch, and Roaring Forks.

9. Or have favorable locations where ponding can be established, such as with installation of beaver dam analogs.

10. Besides an intact dam at Scotch, just upstream is a flood plain with washed-out structures that could be renovated.

11. Information from field examinations logically would be an important part of assessing potential nominee streams...

12. With findings valuable for planning the protection and preservation of both cutthroat and wild trout populations

  I. Evidence​

1. Placements, or translocations, to create protected (isolated) cutthroat populations have not been not sure things.

2. Less than half of 65 separate efforts with cutthroat translocations in Colorado and New Mexico were successful [5].

3. Roughly a third had reinvasion of non-native species [5].

4. Placement of 2 or 3 serial barriers may increase the opportunity for success and aid the removal of non-natives.

5. As well, it may be logical to design barriers specifically to shed high flows to minimize loss of barrier integrity.

6. In a quarter of the translocation efforts, habitat was found to be unsuitable for sustaining populations [5].

7. Trout vary their habitat uses pertaining to flow, substrate, stream structure, and temperature over their life cycle [5].

8. Accommodation of that goes to habitat quality, to which should be added potential resilience to dewatering.

9. Indicated above, stream or reach length, drainage area, habitat volume (flow), and maximum elevations may be key.

10. Existing population success in nearby watersheds having similar characteristics could be useful initial evidence.

11. Contemplating streams or reaches in the Dolores basin as possibilities for placements has important considerations.