Nooksack dace (Rhinichthys cataractae) COSEWIC assessment and status report: chapter 6

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Distribution

• Global Range
• Canadian Range

Global Range

Nooksack dace are restricted to western Washington State and southwestern British Columbia (Figure 2) where they inhabit the drainages of the east shore of Puget Sound, the western side of the Olympic Peninsula and the Fraser River Valley. The historical range is unknown, but unlikely to have been much more extensive as the Columbia-Fraser form of R. cataractae occupy drainages to the west and north with a zone of past or present overlap (see Genetic Description) and other members of the same clade occupy drainages south of the Columbia River (McPhail, pers. comm. 2006).

Figure 2: The Global Range of the Nooksack Dace is Restricted to Northwestern Washington State and the Fraser River Valley in Southwestern British Columbia

Adapted from McPhail (1997) and Mongillo and Hallock (1997).

Canadian Range

Within Canada Nooksack dace occupy a restricted range consisting of four creeks in two major watersheds of the Fraser Valley (Fig. 3). Three of the creeks flow south into Washington State’s Nooksack River (Bertrand Creek, Pepin Creek and Fishtrap Creek). The fourth population, discovered in 2004, occupies the Brunette River, a tributary of the lower Fraser River. The nearby Coquitlam and Alouette Rivers, also tributary to the Fraser River, contain either sympatric populations or introgressed hybrids of Nooksack dace and Columbia-Fraser R. cataractae (see Genetic Description).

The extent of occurrence in Canada comprises 630 km², or 4.3 percent of the global extent.  Potential habitat, defined as the total riffle area in reaches containing more than 10 percent riffle by length, totals 7 328 m² in three of the four Canadian populations (Table 1). Much of this habitat is currently unoccupied due to seasonal drying, compaction with silt or beaver impoundment. Habitat in the fourth occupied watershed, the Brunette River, has yet to be surveyed, but the total riffle area available is 20 155 m².  This gives a total riffle area (area of occupancy) of 0.03 km². The area of occupation in Washington State is unknown. Area of occupancy estimated from an overlaid grid of cell size one km² is in the order of 14 km².

*Pearson, Unpublished data
Potential habitat consists of riffle areas in reaches containing more than 10% riffle by length. Maximum population estimates are products of density in high quality habitat (1.9 per m², Inglis et al., 1994) and available riffle area. A CPUE-based estimate of relative abundance among watersheds (Pearson, 2004) is used to calculate the adjusted estimate. See Population Sizes and Trends for discussion.

The existence of unknown populations in other Fraser River tributaries seems plausible in light of the recent confirmation of the Brunette River population. Searches of occurrence records for R. cataractae in the Fraser Valley using the UBC Fish Museum database and the British Columbia Fisheries Inventory Summary System and the Royal British Columbia Museum records yielded putative records from 36 sites in the Fraser Valley (Table 2). Those from areas not yet genetically characterized are shown in Figure 3.

Within watersheds Nooksack dace distribution is extremely clumped. Pearson (2004) compared catch per unit effort (CPUE; mean number of fish per trap; 24 h sets) in 72 reaches of the Nooksack River tributaries. CPUE was zero in most (41) reaches and high densities (CPUE>0.25 fish per trap) were found in only 8 reaches, 6 of which are contiguous in lower Bertrand Creek. He estimated that this 5 km stretch of channel constituting just 12.5% of mainstem length in the Nooksack River tributaries contained more than 70% of their Nooksack dace.

Historical changes in the Canadian distribution are poorly documented, but a general decline over at least the past half-century seems likely. McPhail (1997) reports that Nooksack dace were extirpated from some headwater tributaries of Bertrand and Fishtrap creeks between the late 1960s and the mid-1990s. Pearson (2004) found them only in the main stems of these creeks, and observed that most of the tributaries run dry in late summer.

¹ http://www.zoology.ubc.ca/~etaylor/nfrg/fishmuseum.html
² http://www.env.gov.bc.ca/fish/fiss/
³ As identified by McPhail:     CF = Columbia-Fraser   N = Nooksack    ?= not tested
⁴ Mission

Figure 3: In Canada, Nooksack Dace Populations are Confirmed in the Brunette River (A, 2004), Bertrand Creek (B, 2005), Pepin Creek (C, 2004), and Fishtrap Creek (D, 2004)

Norrish Creek (G) contains the Columbia-Fraser form of R. cataractae, while the Coquitlam River (E. 2004) and Alouette River (F, 2005) contain either sympatric populations or introgressed hybrids of the two types (J.D. McPhail unpubl. data). Years refer to date of most recent captures (Pearson, unpubl. data). Numbers refer to putative R. cataractae records from other watersheds as detailed in Table 2.