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BarrierB&W_edited_edited.jpg

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  • Many study area streams have mixed trout populations.

  • Moving wild trout from native cutthroat habitat increases the opportunity for natives to survive, even prosper.

  • Declining stream flows due to climate change increasingly stress cutthroat populations.

  • That's in addition to habitat competition from brook and brown trout, and population hybridization from rainbows.

  • Barriers for separating populations are logical where the purpose is to protect natives.

  A. Approach​

  • Install exclusion barriers to minimize additional entry of wild species into cutthroat habitat. (See references 1-4 below.)

  • Apply electro-winnowing to remove and relocate wild trout that are above the barrier.

  • Use existing structures, such as culverts (exhibits 1 & 2) and bridges, for cost-effective and resilient barrier placements.

1. Looking upstream at the barrier

Upstream_edited.jpg

2. Looking downstream at the barrier

Downstream_edited.jpg

  B. Installation

  • Wood planks, 2-in x 6-in, were used at the culvert installation seen above in exhibits 1 and 2.

  • A single barrier in a concrete culvert is shown schematically in exhibit 3.

  • Exhibit 4 shows double walls holding rock between, which uses barrier length, not just height, for blocking intrusions.

  • A concrete pad installed just downstream has been described as functioning as a barrier to trout entering the culvert.

  B. Installation, cont.

  • That is, the pad could prevent scouring and creation of a plunge pool from which trout could launch into the culvert [5].

  • Exhibit 5 shows concrete and steel culvert locations and a bridge at streams in the study area.

  C. Preferences​

  • Preferred sites have structures that are more resilient to erosion than the streambed and its directly adjacent riparian areas.

  • For example, concrete or steel culverts can serve well, as can posts and planks that support bridges.

  • They enable solid anchoring of barriers, which minimizes the opportunity for them to be damaged from high water velocity, such as during snowmelt.

  D. Electro-fishing

  • Electro-fishing can be conducted to capture and identify trout species above a barrier.

  • And also to remove, or winnow, non-native species from the stream.

  • The technique is demonstrated in the brief video below.

  • Small tail samples of netted natives also can be collected for DNA analysis to determine genetic heritage.

  • Fish caught by this approach recover virtually immediately.

  • The non-native species netted can be relocated.

3. Electro-fishing for trout species identification and winnowing

4. Concrete and steel culverts and a bridge at streams in the study area

Culverts.jpg

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