Research Document - 2007/058

An Assessment of Potential Critical Habitat for Nooksack Dace (Rhinichthys cataractae ssp.) and Salish Sucker (Catostomus sp.)

By Pearson, M.

Abstract

Potential critical habitat (PCH) is defined for Salish sucker and Nooksack dace. PCH is identified and mapped using reach-scale, in-stream habitat characteristics. PCH includes 166 km of channel and 328 km of bank in 140 reaches and 11 watersheds. The width of riparian reserve necessary to maintain important habitat characteristics is included in PCH and was assessed using an adaptation of British Columbia’s Riparian Area Regulation (RAR) assessment methodology. It extends laterally from the top of bank along both banks of the full length of each potential critical habitat reach to a distance equal to the widest zone of sensitivity (ZOS) calculated for each of 5 riparian features, functions and conditions. These are: large woody debris supply for fish habitat and maintenance of channel morphology, localized bank stability, channel movement, shade, and insect and debris fall. Widths of riparian reserve in PCH reaches range from 5 to 30 m, with an average of 21.4 m (s. dev = 6.77) and total area encompasses 717 ha of land.

Existing riparian vegetation in PCH is sparse, with 60% of bank length supporting discontinuous bands of vegetation less than 5 m wide. This highlights the need for recovery activities focused on riparian enhancement and restoration. Permanent structures such as roads, farm crossings, buildings, and yards restrict the width of 106 km (32%) of riparian reserve within PCH to less than its calculated value. Actively farmed land and golf course fairways impinge on an additional 112 km (34%) of PCH length. Protecting this land is a priority for conserving these species and would provide benefits to a number of other SARA listed species, in addition to salmonids, surface water quality, and (in many cases) agricultural drainage.

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