COSEWIC assessment and status report on the Rocky mountain ridged mussel Gonidea angulata in Canada
- Assessment Summary
- Executive Summary
- Species Information
- Population Sizes and Trends
- Limiting Factors and Threats
- Special Significance of the Species
- Existing Protection or Other Status
- Summary of Status Report
- Technical Summary
- Literature Cited
- Biographical Summary of the Report Writers
- Authorities Consulted
- Collections Examined
The range of G. angulata is described as “Southern British Columbia to southern California, eastward to southern Idaho and northern Nevada” (Taylor 1981). Burch (1975) described the range as central California, north to British Columbia and east to Nevada and Idaho. Currently, G. angulata is known from portions of western North America only, mostly south of the Wisconsinan glacial margin. West of the Cascades, G. angulata is seemingly absent from the Olympic Mountains, Washington and points north, but occurs sporadically in the Willapa Hills (southwest Washington) and northwest Oregon, and occurs more continuously from southwest Oregon south to southern California. East of the Cascades, G. angulata occurs in the interior of Washington and Oregon, in southern Idaho and in northern Nevada.
Taylor (1981) described its distribution in California as “formerly throughout most of the State, in the following drainages: Lower Klamath, upper Klamath River and Lost River; Pit River; Central Valley; north coast streams (lower Eel River and lower Russian River); Clear Lake (including Blue Lakes); Pajaro-Salinas system (Pajaro River only); Los Angeles Basin (Ballona Creek and Santa Ana River). Probably extinct in most of the Central Valley and southern California.” This suggests both a somewhat patchy original distribution and a considerable recent reduction in historic range.
Henderson (1929, 1934, 1936 a,b) provides information on some interesting sites, including claims for distribution in Utah and Montana. One of the authors (TJF) was unable to confirm Utah and Montana sites from museum records. Chamberlin and Jones (1929) do not list this taxon from Utah.
Gonidea angulata has been found in the Columbia River system in southern British Columbia (Okanagan and possibly the Kootenay) (Clarke 1981) and is known in Canada only from the main, valley-bottom water bodies from Penticton south to the border and the only recent museum records (1991) are from the following areas:
Okanagan River at Okanagan Falls,
and Osoyoos Lake.
Given the current distribution of G. angulata in the Columbia River and associated tributaries in northeastern Washington, it is probable that G. angulata is present in some equivalent portions of southern British Columbia (i.e., in areas not currently documented as occupied or known breeding areas).
Figure 3. Historical range of G. angulata in British Columbiaand the Pacific Northwestern United States.
Figure 4. The distribution of Gonidea angulata in British Columbia. Black dots represent the approximate location of known sites (from museum records and/or recent collections). Named tributaries of the Okanagan River represent the potential range for this species.
Table 1 identifies some recent records of G. angulata in B.C. (from Taylor (1993) and from museum records). However, addition of new sites would not likely increase the extent of occurrence (209 km2) significantly. The actual area of occupancy is estimated at 31.5 km2, but is much less than 100 km2.
*Canadian Museum of Nature records only
To determine if G. angulata persists within its historical (and only known) range in British Columbia, several organizations were contacted to discuss whether or not individuals in the area had seen this species. In particular, the Osoyoos Lake Water Quality Society was contacted and the potential presence of this mussel was discussed. Subsequently, all members of the Osoyoos Lake Water Quality Society were alerted to the potential presence of G. angulata, and as a society initiated informal searches for this species (i.e., individuals or small groups would include visual searches for shells or live mussels as part of their activities during walks). Searches were conducted along the Okanagan River and its tributaries, and around the shores of Osoyoos Lake. As of 2 August 2002, 1 specimen has been positively identified as G. angulata and this specimen consists of half of a shell (Figure 5). The specimen was collected from Park Rill Creek within the town limits of Oliver, B.C.. Unsubstantiated information suggests that there are live specimens within Park Rill creek and other nearby tributaries of the Okanagan River near the area where the shell was collected (L. Dallas, pers. comm). To determine if the named tributaries in Figure 4 represent suitable habitat or house extant populations of G. angulata, extensive surveys and research to determine population sizes in each watershed would be required.
Figure 5. Scanned images of the G. angulata shell collected from Park Rill Creek, British Columbia, 23 April 2002. Photo V.C. Hawkes, collector: L. Dallas.
Total documented Canadian locations are 8 with only 1 of these confirmed as extant (Park Rill Creek). It is not known if this species has disappeared from historical sites.
For other recent records of G. angulata from the western United States, see Taylor (1981), Neitzel and Frest (1993); Frest and Johannes (1991, 1992, 1993, 1994, 1995a, 1998, 2000).
- Date Modified: