Habitat Enhancement Construction (2017 & 2018)
The design principles for the artificially enhanced spawning habitat
combined parameters used for anadromous salmonid habitat installations
with characteristics of rehabilitation projects in rivers and artificial
spawning reefs constructed in lakes for lacustrine populations of lake
trout and lake whitefish (Bronte, Schram, Selgeby, & Swanson, 2002;
Fitzsimons, 1995; Manny, Edsall, Peck, Kennedy, & Frank, 1995; Mohr &
Nalepa, 2005). Key design factors included substrates that matched
documented lacustrine lake trout and coregonid spawning shoals, which
incorporated interstitial spaces for egg protection (Claramunt et al.,
2005; Gatch et al., 2020; Marsden et al., 2016; Marsden, Perkins, &
Krueger, 1995; Sly, 1988). Design criteria encompassed a minimum
spawning bed thickness of 0.3 m, substrate sizes ranging from
approximately 5 to 30 cm, a preference for angular cobble and gravel to
maximize interstitial spaces, and ensuring final spawning elevations
remained ice-free during winter (at least 1.0 m depths during fall flow
conditions).
In the summer of 2017, the first phase of the habitat enhancement
project commenced, targeting a 40 m2 area of
moderately deep run habitat in lower Reach 1. The selected location
predominantly consisted of bedrock with some patches of boulder, and the
measured mean depth was 1.8 m prior to installation. The initial step
involved adding a base layer of boulders sourced from the shoreline to
provide stability and heterogeneity of cover for fish. The area was then
filled with crushed gravel and cobble, which was thoroughly washed on
the shoreline to remove fines before being transferred by boat to the
spawning bed location. Upon completion of the first phase in 2017, the
total surface area of bedrock covered by the placed substrate measured
approximately 9 m2 (see Supplementary Information
Photo 2). The composition of the substrate on the completed spawning bed
was visually estimated as 50% cobble, 35% gravel, and 15% boulder.
In the subsequent summer of 2018, using the same methods and materials,
the area of the artificially enhanced spawning bed within Reach 1 was
expanded approximately four times its original size. This expansion
aimed to cover all exposed bedrock in the area, resulting in a total
installed habitat area of 40 m2 in the study reach
(Figure 1).