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Recovery Strategy for Nooksack Dace
The status report and assessment summary for Nooksack Dace is available from the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) Secretariat (www.cosewic.gc.ca).
Common Name: Nooksack Dace
Scientific Name: Rhinichthys cataractae
Assessment Summary: May 2000
COSEWIC Status: Endangered, April 1996
SARA Status: Endangered, June 2003
Reason for Designation: This species has a restricted range in Canada, and is in significant decline due to habitat loss and degradation. Range in Canada: British Columbia Status History: Designated Endangered in April 1996. Status re-examined and confirmed in May 2000. Last assessment based on an existing status report.
The Nooksack dace is a small (<15 cm) stream dwelling cyprinid (minnow). The body is streamlined with, large pectoral fins and a snout that overhangs the mouth. Body colouration is grey-green above a dull, brassy lateral stripe and dirty white below it. There is often a distinct black stripe on the head in front of the eyes, which in juveniles continues down the flanks to the tail (McPhail 1997). The Nooksack dace is considered a subspecies of the widespread and common longnose dace Rhinichthys cataractae (J.D. McPhail, University of British Columbia, pers. comm.). It evolved through geographic isolation in Washington State’s Chehalis River valley sometime during the Pleistocene glaciations (McPhail 1997). Adults are generalized insectivores while juveniles feed on zooplankton (McPhail 1997).
Populations and Distribution
Populations are documented from four lowland streams in British Columbia’s Fraser Valley (Figure 1). The global distribution consists of approximately 20 additional streams in north-west Washington State. The species is extirpated from some tributaries within Canadian watersheds where it was abundant in the 1960s (McPhail 1997). The current status of Washington State populations is unknown. Based on available information, Canada contains approximately 10% of the global range and 20% of all populations (Figure 1).
Description of the Species Needs
Biological Needs, Ecological Role and Limiting Factors
The major factor limiting population abundance and distribution is the availability of high quality habitat (see below). Given adequate habitat Nooksack dace populations should recover rapidly as their life history characteristics promote rapid population growth. They are small-bodied, mature early(2 years, McPhail 1997), and have an extended spawning period and may spawn more than once each year (April - July, Pearson 2004a), a trait that increases fecundity in species otherwise limited by small female body size (Blueweiss et al. 1978; Burt et al. 1988).
Figure 1: Canadian and global distribution of Nooksack dace. In Canada the Nooksack dace is known to inhabit four watersheds (left panel; 1- Brunette River, 2 – Bertrand Creek, 3 – Pepin Brook, 4 – Fishtrap Creek). Globally, it is also found in a number of other streams in northwestern Washington (right panel, adapted from McPhail 1997).
Nooksack dace are riffle specialists. The proportion of riffle habitat in a reach is the strongest predictor of their presence and they are rarely found in reaches with less than 10 percent riffle by length (Figure 2) or in reaches where long stretches of deep pool habitat separate riffles (Pearson 2004a). Young-of-the-year fish require shallow calm, pool habitats in close proximity to riffles. Most individuals appear to have small home ranges (tens of metres of channel) although a small number of individuals venture hundreds of metres. Clusters of riffles may contain semi-isolated subpopulations. Distances and barriers between clusters may influence long-term population persistence by altering watershed scale population dynamics.
Figure 2: Nooksack dace are found in fewer than half of reaches that contain less than 10 percent riffle by length. Numbers over bars indicate sample size (adapted from Pearson 2004a).
Riffles are among the shallowest of stream habitats and consequently among the first to shrink when flow declines. When surface flow ceases, riffle habitat is entirely eliminated and Nooksack dace may be forced into pools, a non-preferred habitat where foraging success and security from predation may be compromised.
Little information exists on tolerances or preferences of Nooksack dace for parameters such as dissolved oxygen, pH, and temperature. Activity appears minimal at temperatures below 11 oC , and fish forage normally at temperatures in excess of 20 oC (Pearson 2004a). Nooksack dace are likely poorly adapted to
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