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).