Research Document - 2007/075
Recovery Potential Assessment for the Nooksack Dace (Rhinichthys cataractae)
By Harvey, B.
Abstract
Nooksack dace is a close relative of longnose dace, a freshwater minnow widely distributed in North America. The Nooksack subspecies is found in only four rivers in Canada, all of them in the Fraser Valley. Three of these rivers are in the Nooksack River basin and flow south into Washington State; the fourth (Brunette River) is a tributary of the Fraser River. Most Nooksack dace habitat is in the United States.
The Nooksack subspecies was designated Endangered by COSEWIC in 1996, with an updated status report in 2000. The B.C. Conservation Data Centre classifies the subspecies as S1 (Critically Imperiled). Nooksack dace was listed as Endangered (Schedule 1) under the Species at Risk Act (SARA) in 2003. As a member of the “Chehalis fauna”, a group of fishes that emerged in unglaciated areas south of Puget Sound and diverged from those in the Columbia drainage, the subspecies has considerable scientific interest for evolutionary biologists.
Nooksack dace spend most of their lives near the bottom, within restricted stretches of river, with a strong preference for riffles (areas of faster-moving water). Population sizes for Bertrand, Pepin and Fishtrap Creeks are uncertain and have been estimated using an indirect process. They are: Bertrand Creek: 5,700; Pepin Creek: 800; and Fishtrap Creek: 300. There are insufficient data to describe any trends in abundance.
Critical habitat for Nooksack dace is defined as “reaches in their native creeks that contain or are known to have previously contained more than 10% riffle by length.” The human activities that most threaten Nooksack dace in Canada are those that alter, destroy or break up critical habitat. The threats to dace habitat are the result of more than a century of agricultural, industrial and urban development of the Fraser Valley. They include physical destruction, seasonal low flows, sedimentation and fragmentation. Nooksack dace habitat continues to be lost to flood control and agricultural drainage projects. Riffles and marginal pools are the most affected.
There are options not only for reducing the instances of habitat destruction and fragmentation, but also for minimizing their effects. The first approach relies on using our knowledge of the threats, their effects and the existing regulatory mechanisms to develop reach-specific best management practices. The second approach accepts that habitat loss has already occurred, and concentrates on remediation. Restoration of damaged habitat, creation of new riffle habitat and riparian planting are all technically feasible.
Alternatives to activities that affect dace habitat include removing land from agricultural production. One model is the Conservation Reserve Enhancement Program (CREP), a voluntary land retirement program administered by the United States Department of Agriculture’s Farm Service Agency (FSA). A Canadian alternative that concentrates on best practices and restoration of riparian lands in the Fraser Valley could follow the lead of successful large-scale wildfowl habitat restoration projects undertaken by land trusts and their partners in B.C.
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