Speckled dace (Rhinichthys osculus) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

Search effort

The known distribution within the Kettle River system is a result of field work conducted during museum collections and rainbow trout population assessment studies. It is possible that speckled dace occur in areas of the mainstem upstream of the known distribution that have not been systematically surveyed. Recent rainbow trout surveys in the Kettle and West Kettle systems have not found dace in tributaries (BC Ministry of Environment unpubl. data). Peden and Hughes (1981) found young-of-the-year speckled dace were widely distributed and relatively easy to capture during September and October, whereas adults were more difficult to find. More recent sampling has focused on the area of the power project at Cascade Falls where a relatively high abundance was found (Peden 2002, PDI 2005, BC Ministry of Environment upubl. data). Swim surveys conducted in 2005 suggest that speckled dace are found in the Kettle and West Kettle rivers in areas where specific riffle habitat is available (Ron Ptolemy, Aquatic Ecosystem Science, Ministry of Water, Land and Air Protection, Victoria, BC; pers. comm. 2006).

Abundance

No systematic quantitative sampling has ever been completed over the range of speckled dace in Canada.

Fluctuations and trends

There have been no long-term studies of speckled dace or detailed studies of their habitat that could provide information on trends in abundance. Surveys during 1978 to 1980 indicated populations were stable over that short period (Peden and Hughes 1981). Peden and Hughes (1984) speculated that there may be fluctuations in survival of young-of-the-year fish as a consequence of variability in spring flooding, but also noted that speckled dace evolved within the natural flood regime of the river and may have developed adaptations to cope with natural patterns of disturbance. In other systems annual estimates of specked dace abundance can fluctuate considerably (e.g. Pearsons et al. 1992). Fish habitat problems related to low summer flows are a result of a combination of irrigation/diversion, land use practices and low summer flows; to some extent it is not a natural phenomenon and is likely to get worse over time. As a consequence of such habitat reduction, invertebrate production in riffles and speckled dace numbers may be declining.

Rescue effect

Speckled dace in Canada are isolated above a 30.5 m high barrier at Cascade Falls. The Kettle River above Cascade Falls does loop down into the US and speckled dace in this section are likely able to move across the border into Canada. This section is only about 45 km long with an extent of occurrence of about 2 kmĀ². These fish, however, could also be affected by the same event affecting speckled dace in Canada, if the event were to occur upstream of the US section of the river.

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