Influence of beaver mimicry restoration on habitat availability for fishes, including Arctic grayling (Thymallus arcticus)

Beaver-dam-mimicry is an emergent conservation practice. We evaluated the
influence of constructed riffles, a unique type of beaver mimicry aimed to
store water and allow fish passage, on habitat for fishes in one control
reach and one manipulated reach with mimicry structures added. The beaver
mimicry reach had deeper pool habitats and deeper and wider riffle
habitats compared to an unmanipulated control reach. Dissolved oxygen was
similar among reaches, averaging 8.7 ± 0.2 and 8.9 mg/L in the beaver
mimicry and control reaches, respectively. Sediment size was also similar
among reaches, with a D50 of 8.1 and 10.6 mm in the beaver mimicry and
control reaches, respectively. The beaver mimicry reach had little to no
overhanging bank vegetation or riparian vegetation shade cover, while the
control had 38% of its bank covered by canopy and 56% overhung by
vegetation. These riparian characteristics result from a legacy of
livestock grazing and lack of consistent vegetation planting during
restoration. Longnose dace (Rhinichthys cataractae) and white sucker
(Catostomus commersonii) dominated in the beaver mimicry reach, together
comprising 70% of the fish assemblage post-structure installation. Arctic
grayling (Thymallus arcticus) were not found in the beaver mimicry reach
but were present in the control, albeit in small numbers of only 3% of the
assemblage post-structure installation. These results highlight the need
to consider both in-stream and riparian habitat features for fishes, as
well as timescales of both hydrological and ecological outcomes in
restoration design.