Speckled dace (Rhinichthys osculus) COSEWIC assessment and status report: chapter 8

Limiting Factors and Threats

Haas (1998) listed the limited distribution and small total population size as important risk factors for speckled dace in Canada. Additional threats on the list included forest harvesting activities, habitat loss, exotic species introductions, urbanization, agricultural and industrial pollution, hydroelectric development (see Habitat trends) and accumulations of coal slag on the Granby River at Grand Forks, BC.

The entire range of speckled dace in Canada is found within a single drainage system (known extent of occurrence = 7.47 kmĀ²). Of the habitat sampled to date the 11.4 km section just above Cascade Falls supported the highest densities of speckled dace and may represent a significant proportion of the adult Canadian population (Peden 2002). This requires confirmation by additional sampling of habitat in the upper watershed. A major catastrophic event, capable of causing downstream impacts, could threaten a significant portion of the population in this area (Peden 2002). It is unlikely, however, that a single catastrophic event could affect all of the speckled dace in Canada as they occur in more than one river. Re-colonization would most likely be possible from portions of the distribution that were not impacted.

Due to low summer flows, the dominance of small particles (gravel and sand) and limited instream cover, adult habitat may be the limiting factor for several fish species in the Kettle and West Kettle rivers (Sebastian 1989). Habitat in the lower Granby River is similar. Significant numbers of large speckled dace have only been found in areas that contain cover (undercut banks and larger substrates such as cobbles and boulders) with an absence of fine materials, in good depth and current (Peden 1981, 2002).

The Kettle River system by nature is considered a flow sensitive system with threats from water abstraction. It occurs in an ecoregion of relatively low, normal unit run-off (265 mm/year). This problem has become increasingly accentuated by increasing draws on water for urban, agricultural and industrial needs in the watershed. Climate warming has the potential to further exacerbate this condition. Based on the observed frequency of drought-like conditions in the system (Fig. 5 and figure6) additional extraction cannot in reality meet fish needs (R.A. Ptolemy pers. comm.). The Tennant Method for instream flow assessment describes instream flows of 10% MAD as poor or minimum habitat for fish and wildlife (short term survival only in most cases); at flows below 10% MAD habitat is considered severely degraded (Tennant 1976; Annear et al. 2004). Tennant described 30% MAD as the generic threshold at which depth and velocity in riffles are adequate for fish and aquatic insects; below 10% MAD the depth, velocity and width of riffles were described as severely degraded. Figure 5 shows that during the 2003 drought, flows dropped below the minimum of record for an extended period of time (weeks). In addition to the loss of riffle habitat, low-flow conditions can result in elevated water temperatures, reduced dilution potential and degraded water quality (waste discharge), reduced dissolved oxygen levels, and increased vulnerability to terrestrial and aquatic predators. In the winter low-flow conditions can increase the risk of freezing and low dissolved oxygen levels. Increasing water temperatures are not expected to impact speckled dace; it is the other conditions which may impact abundance through habitat loss and impacts to food supply.

Increasing water allocations may not be the only factor affecting low flows; climate change may also play a role in the decrease in low flows seen between the years prior to 1963 and the period after 1981 (Aqua Factor Consulting Inc. 2004). Both provincial and federal fisheries agencies have expressed concerns that low water flows combined with high temperature are causing excessive stress, reduced rearing capacity, and mortality in fish residing in the Kettle River system.

Climate warming has the potential to increase the severity, duration and frequency of drought conditions. The flows measured in the Fraser River at Hope indicate that the date by which one-third and one-half of the annual cumulative flow occurs has advanced by 11 and nine days respectively each century (Aqua Factor Consulting Inc. 2004). Streams in south central BC show a similar trend with an earlier spring freshet and lower flows in late summer and early fall (Aqua Factor Consulting Inc. 2004).

Early summer fish kills within the areas of the river occupied by speckled dace were reported in the Kettle River in 1991, 1992 and 1998 (Aqua Factor Consulting Inc. 2004). The dead fish reported included whitefish, trout, and suckers. These three incidents took place prior to the low flow period of late summer and early fall and they appeared to be localized. The cause of these fish kills has not been determined.

Peden and Hughes (1981) found speckled dace were absent or low in abundance in apparently suitable areas downstream of the sewage treatment plant at Grand Forks and what may have been usable habitat near the lumber mill at Midway, suggesting that changes in water quality may have had an impact in these areas. Peden (2002) listed additional threats including the activities in the US (upstream of Cascade Falls) that could have deleterious impacts downstream in Canada, and road construction or agricultural practices that could cause siltation of substrate materials and/or chemical contamination.

The proposed power project has been dealt with under Habitat trends above, but it should be noted that the current proposal is only expected to impact a very small percentage of speckled dace habitat in the Kettle system.

Page details

Date modified: