Substrate Cover and Nooksack Dace

The final curve was based on relationship between % cobble substrate cover and Nooksack Dace density identified in Gray et al. (2024) using empirical data. We capped the maximum habitat capacity at 80% to prevent unrealistically high predicted capacity using the Gray et al. (2024) power function between dace density and % cobble. (see Fig. below). The habitat suitability curve for Longnose Dace (Edward et al., 1983) also generally supports a positive association between % cobble cover and system capacity. Note that while there is a generally positive overall relationship between cobble substrate and dace density, the variance around the line is large, particularly at higher cobble substrate cover. While we can be reasonably confident that dace abundance increases up to 20-40% cobble cover, it could also be reasonable to assume that it plateaus above this level as implied by the Edwards et al. (1983) curve for Longnose dace. At the expert elicitation workshop held in November 2024, John Gray indicated that Dace may even prefer larger substrate (i.e. boulder) and that a SR for boulder would be similar to the one for cobble. Therefore, for the x-axis of this SR function %cobble and boulder combined is more appropriate for more general application to streams/reaches that actually have boulder-sized substrate present.