Science Advisory Report 2008/031

Recovery Potential and Potential Critical Habitat for the Nooksack Dace (Rhinichthys cataractae sp.)

Summary

• Nooksack dace are found in only four rivers in Canada, all of them in the Fraser Valley; the species is thus restricted to a geographic area where human impacts on dace habitat have been intense for more than a century.
• There are no data or analyses presented for Nooksack dace to counter the original COSEWIC criteria identifying declining habitat quantity and quality as the main factors jeopardizing survival or recovery.
• Nooksack dace is one of many data-poor freshwater fish species that are COSEWIC- designated. The main source of uncertainty is in estimating abundances and capacity of the four populations.
• The stream "reach" is an appropriate assessment scale for Nooksack dace abundance and habitat. Potential critical habitat for Nooksack dace includes reaches in their native creeks that contain or are known to have previously contained more than 10% riffle by length. Riparian habitat is also deemed important for population recovery.
• There is little scope for human-induced mortality or alternative habitat configurations. Permitting of activities that cause incidental mortality or that alter potential critical habitat should consider the consequences for achieving stated recovery goals in a risk management context that considers the high uncertainty in the data.
• Habitat restoration is essential for the survival and recovery of Nooksack dace, but research on the function of potential critical habitat in relation to population survival or recovery is recommended to establish restoration priorities.
• Severe low flow during high water-use periods results in completely dry riffle habitat in some reaches, especially in Bertrand Creek. An immediate mitigation measure would be to reduce drying and its obvious direct impact on survival.

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