Research Document - 2007/074
Scientific information used in the recovery potential assessment for the speckled dace (Rhinichthys osculus)
By Harvey, B.
Abstract
Speckled dace Rhinichthys osculus is a small, bottom-living, minnow-like river fish. While common in the western United States, its geographic range protrudes into Canada in one place only: the Kettle-Granby River drainage in the west Kootenay area of southern British Columbia. Speckled dace have been observed in approximately 300 km of river here; availability of suitable riffle or other fast water habitat has been suggested as the main factor limiting its abundance. COSEWIC designates the species as Endangered because of its isolation in a single drainage basin and the impossibility of re-colonization after a catastrophic event. It is not listed under the Species at Risk Act (SARA).
Abundance is poorly known; best estimates range from 11,546 to 23,092 fish. Lack of any consistent census means we have no knowledge of trends in abundance, which appears to vary dramatically depending on time of year and water flow. A quantitative target abundance for speckled dace cannot be established without better census data. To set a generic lower benchmark when the population is not necessarily declining may ignore the purpose of recovery targets.
As a stream-dwelling species that appears to prefer fast-water riffle habitat, the speckled dace can potentially be affected by long-term changes in water volume and velocity. Concerns have been raised that increasing withdrawal for irrigation may affect the population. Instream flow rates based on a percentage of mean annual discharge have been proposed to conserve habitat such as that preferred by speckled dace in the Kettle River, but there are insufficient data to allow us to quantify the expected harm to dace at different flow rates. Ensuring adherence to any benchmark is complicated by the wide margin for further surface water extraction under existing licenses, unlicensed withdrawal of ground water and a poor understanding of the connection between surface water and aquifers. Licensing of groundwater extraction, further research to determine the connection between surface and ground waters in the basin, and alternative agricultural practices, including trickle irrigation, are proposed.
A proposal for a 25-megawatt run-of-river hydroelectric generation project at Cascade Falls on the Kettle River was approved in 2006 after modification to reduce potential fish habitat impacts. A qualitative risk assessment supported by a quantitative population viability model concluded that the project posed a negligible risk to the speckled dace population. The procedure followed in determining its potential impact on speckled dace could be applied to any subsequent proposed activities on the river that could disrupt fish habitat.
Infestation by mountain pine beetle (Dendroctonus ponderosae) could degrade stream habitat through collapse of dead trees (reducing stream canopy and increasing snowpack), as well as through salvage logging that further exacerbates flooding. Logging damage to stream habitat can be minimized in various ways that reduce runoff, maintain diversity of cover and avoid sensitive terrain.
In interior B.C. streams, climate change is expected to increase the number and severity of droughts. For flow-sensitive species like speckled dace, such alterations may be of concern.
A model developed to allow contemplation of various scenarios for removal of speckled dace habitat by the Cascade Falls hydropower project demonstrated that it was possible to make some quantitative predictions for a data-poor species like speckled dace. Development of alternative models for dace population viability depends on better knowledge of abundance, spatial distribution, habitat availability and recruitment.
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