Speckled dace (Rhinichthys osculus) COSEWIC assessment and status report: chapter 4

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Distribution

Global range

The range of speckled dace is restricted to western North America (Fig. 2); it is found in Pacific drainages from the Columbia River south to the Colorado River system, and in coastal drainages between the Olympic Peninsula and southern California in a variety of morphological forms (Scott and Crossman 1973, McPhail 2003).

Figure 2. The global distribution of speckled dace, Rhinichthys osculus (with permission of Dr. J.D. McPhail).

Canadian range

Speckled dace reach their northern limit in south central British Columbia (BC) (Fig. 3) where they are found only in the Kettle-Granby river system (Columbia drainage) of BC (Peden and Hughes 1981 and 1984; Peden 2002). The vast majority of their Canadian distribution is isolated from other speckled dace populations and other Rhinichthys species (Haas 2001; McPhail 2003) by a 30.5 m barrier at Cascade. Specifically, they have been collected or observed from Cascade Falls to 194 km upstream in the Kettle River (including the 46.7 km U.S. loop), and the lower 37 km section of the Granby River near Grand Forks, BC (BC Ministry of Environment, unpubl. data), as well as about 75 km of the West Kettle River to Carmi. Peden and Hughes (1981, 1984, 1988) also observed small numbers of speckled dace in the 5 km Canadian section downstream of Cascade Falls to the U.S. border.

Figure 3. Kettle River system of south central British Columbiashowing the distribution of speckled dace, Rhinichthys osculus (B.C. Ministry of Environment map).

Although the data collected to date have been adequate to determine the general range of speckled dace within Canada (known extent of occurrence ~ 3,000 km², based on a best fit polygon), additional survey work could extend the distribution particularly in the mainstem Granby River, as well as headwaters areas of the Kettle and West Kettle rivers and other tributaries. No comprehensive surveys have been completed to accurately determine the area of occupancy. General impressions from snorkeling surveys for salmonids (conducted in 27 km of mainstem river habitat in October 2005) suggest no more than 20% of the mainstem habitat in the Kettle and West Kettle rivers is likely to be occupied by speckled dace, based on the proportion of riffle habitat relative to glide and pool habitat in the river mainstem (A. Wilson pers. comm.). Oliver 2001) stated that the weighted average riffle area for 160 km of the Kettle River is 25%. Extrapolating these observations to the Granby River gives an approximate total area of occupancy of 7.47 km². With respect to limited surveys in other tributaries, no dace were observed during electrofishing surveys that were conducted in Rendell, Rock, Boundary and McCarthy creeks (within 2 km of confluence with Kettle River) in August 2005 (BC Ministry of Environment, unpubl. data).