Bull Trout passage at beaver dams in two Montana streams
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Abstract
Beaver ( Castor canadensis ) translocation and mimicry is an increasingly popular tool for process-based restoration of degraded streams. Processes influenced by beaver restoration include stream-floodplain connectivity, multi-threaded channel formation, enhanced riparian condition and fire resiliency, and streamflow attenuation. Beaver activity can also be a nuisance in agricultural settings, increase invasive species abundance, and create in-stream barriers to fish. Previous studies indicate that spring-spawning salmonid species can pass beaver dams in higher proportions than fall-spawning species. Thus, restoration or mimicry of beavers in streams containing fall-spawning, threatened Bull Trout ( Salvelinus confluentus ) is of concern to many biologists. We evaluated Bull Trout passage at beaver dams in two Montana streams: Meadow Creek (East Fork Bitterroot River drainage) in summer 2020 and Morrison Creek (Middle Fork Flathead River drainage) from 1997 to 2011. In Meadow Creek, 16% of PIT-tagged Bull Trout which entered a large beaver dam complex were detected upstream of some dams, but no fish moved through the entire 1 km complex. In Morrison Creek, redds were more likely than random to be located below dams, but two or more redds were found upstream of at least one dam in 6 of 9 years dams were present. These results suggest that beaver dams can affect the movement of Bull Trout, but that passage depends on the characteristics of individual dams and reach geomorphology. Our methods cannot distinguish between inhibition of fish movement and selection of beaver-created habitats by fish. Therefore, we suggest future research on beaver restoration in streams with Bull trout.
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This Zenodo record is a permanently preserved version of a PREreview. You can view the complete PREreview at https://prereview.org/reviews/10685432.
This paper examines how beaver dams and beaver dam analogues affect passage of bull trout. Using PIT tags, researchers monitored the upstream movement of fish through an area containing multiple beaver dams. Jump heights for bull trout were calculated for each dam. The paper also analyzed how many spawning nests were present and performed statistical tests to determine their randomness. As BDAs increase in popularity as a restoration technique, it is important to monitor how they impact fish movement. Many studies have concluded that BDAs and beaver dams to not impede fish passage; however, this paper is important to the field by examining how one threatened species may be impacted. The …
This Zenodo record is a permanently preserved version of a PREreview. You can view the complete PREreview at https://prereview.org/reviews/10685432.
This paper examines how beaver dams and beaver dam analogues affect passage of bull trout. Using PIT tags, researchers monitored the upstream movement of fish through an area containing multiple beaver dams. Jump heights for bull trout were calculated for each dam. The paper also analyzed how many spawning nests were present and performed statistical tests to determine their randomness. As BDAs increase in popularity as a restoration technique, it is important to monitor how they impact fish movement. Many studies have concluded that BDAs and beaver dams to not impede fish passage; however, this paper is important to the field by examining how one threatened species may be impacted. The study concludes that beaver dams do affect the movement of trout, though more research is necessary. The author recommends continuing with restoration with frequent monitoring.
Major issues
Major concerns for the paper are the organization of data collection for redd counts. It may be beneficial to define a redd early in the intro or methods. The methods for surveying redds are clear, but the random distribution section is very unclear starting at line 194. Clarify what a "number line" is and build from there. Also discuss why redd surveys were not performed at the current site in tandem with trout counts. Adding a broad summary to the redds results section may help clarify, as the number of exclusionary years can get complex.
In figure 1, the map of the state and basin should stay where it is placed with dots or stars to indicate the research sites. The zoomed-in maps of each site would be better suited in the methods section, so the reader has a visual of where the PIT tagging occurs. It could also be helpful in the results section, as the results moves spatially very quickly and is tough to follow the location of the fish at certain dates. However, results follow a clear monthly timeline. Additionally, for figure 2, it may be helpful to define "fork length" and describe what it is measuring.
Minor issues
A minor concern for the paper is the title. This title doesn't hint at any kind of discovery. Even if more research is needed, there were results that suggest beaver dams impact fish passage. Consider adding a neutral effect in the title, such as "Beaver dams impact bull trout passage in two Montana streams." For the abstract, the last 3 sentences could be explained more – how do the characteristics of dams/geomorphology impact fish passage? What does it mean that fish are selecting beaver-created habitats? Later in the paper, it is mentioned that trout may prefer downstream habitat. Does that have anything to do with this previous sentence? Consider removing "only" in line 261 to read "well designed experiments…". Include a recommendation to perform the study with a control in the future.
Competing interests
The author declares that they have no competing interests.
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