Research Document - 2012/065
Information in support of the identification of critical habitat for speckled dace (Rhinichthys osculus)
By T.G. Brown, B. Harvey, and M.J. Bradford
Abstract
Speckled dace (Rhinichthys osculus) is a small, riverine minnow belonging to the family Cyprinidae. Although common in Western North America where hundreds of populations of dace exist from Washington to northern Mexico, it is found in only one drainage in Canada, the Kettle River, and two of its tributaries; West Kettle and Granby Rivers. The Kettle River populations of speckled dace exist at the extreme northern extent of their North American range and it is considered a “peripheral species” that is isolated from the central population by a geographic barrier, Cascade Falls. The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assessed the species as endangered because of its limited range and area of occupancy, existence at only three locations, perceived sensitivity to threats and habitat loss, and lack of any potential for rescue. It was listed as endangered under the Species at Risk Act (SARA) in 2009. Field studies conducted after the COSEWIC assessment and following the SARA listing have greatly increased our estimate of speckled dace abundance, extended their range, and increased our knowledge of habitat utilization.
Speckled dace appear widely and somewhat evenly distributed throughout their range in Canada and suitable habitat is abundant. The entire width of the river is utilized although different life stages may occupy different components of the river channel. It does not appear that speckled dace in the Kettle River are threatened by a single “catastrophic event” that could drastically reduce or eliminate all three populations at the same time.
Reduced summer-autumn discharge is well recognized as a threat (COSEWIC 2006). Reduced discharge is due in part to the nature of the watershed, climatic change, and water withdrawals. This threat is somewhat mitigated by the species’ ability to survive and adapt to low flows and warm summer waters, as noted in the more southerly portion of its global range.
The proposed critical habitat depicts the length of river that will supply the amount of habitat necessary to maintain the population abundance required for the persistence of the species in each of the locations where it is presently found. If we accept that a population of 7,000 fish is the minimum population required for long-term persistence of the species and if we assume three fish/metre is a reasonable estimate of abundance; we arrive at 2.4 km of proposed critical habitat. This will be applied to each of the three upper locations to maintain three populations. The three sections of river we have proposed as critical habitat start at the uppermost site where speckled dace were captured during Batty’s distributional study (Batty 2010) and extend downstream for 2.4 km. This approach minimizes the threats of large water withdrawals (mainly for irrigation in the lower watershed) and riparian removal. It is also likely that larval dace produced at these locations will drift downstream and could potentially repopulate or supply genetic material to lower river sections in the event of a catastrophic or transient threat to lower reaches. However, it was not possible to locate all of the critical river sections upstream of all withdrawals or all cleared agricultural lands. It is important to conduct a detailed assessment within each of the proposed critical habitat sections to verify dace abundance and length of stream necessary for critical habitat.
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