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Upper Extent of Fish

This pool below a small waterfall marks the upper extent of fish in Nevergo Creek, Willamette River basin, Oregon.

The last fish on Nevergo Creek is found in this pool. (Willamette National Forest in the Willamette River basin of Oregon) Photo: B. Penaluna.

The distribution boundary at the upper extent of fish across
North America receives extra attention because stream reaches
with fish are managed differently and often have more protections
than fishless reaches. In western North America, Coastal
Cutthroat Trout (Oncorhynchus clarkii clarkii) are the fish
generally found the highest in their stream networks and are,
therefore, the central focus when considering the upper extent of
fish in streams.

This work is an example of successful coproduction among partners, including USDA Forest Service, Bureau of Land Management, Oregon Department of Forestry, Weyerhaeuser Company, Hancock Forest Management, and Port Blakely.

Research Description:

To understand more about the upper extent of fish, I am working with collaborators across landownerships to understand the relative reliability of various tools to determine the fish distribution boundary. We are using GIS and LiDAR tools, and well as comparing eDNA sampling to traditional electrofishing to inform managers and decision-makers.

Key Findings:

In Penaluna et al. (2021), Coastal Cutthroat Trout eDNA was detected
above the electrofishing last-fish boundary in over half of the streams,
which extends the upstream-leading edge of fish by 50–250 m from the
electrofishing boundary. The success of eDNA relative to electrofishing
in determining the geographic boundary of fish characterizes a significant
contribution to fisheries science by detecting fish in low abundances,
which has direct implications species conservation and for forest
management. We posit that eDNA merits inclusion among the sampling
approaches considered to identify the upper extent of fish. Rather,
multiple approaches could be used for reliability and to account for
methodological shortcomings. Ongoing work with LiDAR suggests
that we can improve our understanding of fish distributions using
geophysical metrics.

A small waterfall marks the end of fish on Muletail Creek, Nestucca River basin.

A small waterfall forms a natural physical barrier that limits the upper extent of fish in Muletail Creek in the Nestucca River basin in the Oregon Coast Range. Photo: USFS.

Field crew member makes their way upstream along Panther Creek.

Hiking upstream in Panther Creek in the Oregon Coast Range in search of last fish, the uppermost extent of fish on that stream. Photo: USFS.

Management Implications:

Land managers can use eDNA to detect last-fish to inform forest management in addition to traditional tools. We suggest that as the discussion of eDNA as a management tool continues it is important to distinguish between the science of eDNA (e.g., methodological sensitivities, limitations) and the implications that are derived from its information (e.g., fish presence). As managers start to incorporate eDNA surveys to detect last-fish, they may want to use more than one criterion to define a positive eDNA detection as part of a decision-making framework. For example, a threshold of a positive eDNA detection could be set for a given number of replicates to separate a consistent series of strong detections from a few weak detections, as well as incorporating information about potential barriers to fish movement and other habitat characteristics (e.g., wetlands, habitat complexity).

See link to RTE Radio 1 (Ireland) radio feature:"Mooney Goes Wild, 1 February 2021." Penaluna section begins at minute 29 of the audio.

Mack Creek form of Coastal Cutthroat Trout from the HJ Andrews Experimental Forest.

A Coastal Cutthrout Trout captured from Mack Creek at the HJ Andrews Experimental Forest in the Western Cascades of Oregon. The form of cutthroat found in Mack Creek is more golden in base color than many cutthroat populations. Photo: Ivan Arismendi.

Selected Publications:

Penaluna B.E., J.M. Allen, T. Levi, I. Arismendi, T.S. Garcia, and J.K. Walter. 2021. Better boundaries: delimiting the upper fish distribution boundary of fish in forested streams with electrofishing and environmental DNA. Ecosphere 12(1):e03332. https://doi.org/10.1002/ecs2.3332 (open access)