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COSEWIC Assessment and Update Status Report on the Redside Dace in Canada

Limiting Factors and Threats

Redside dace populations have declined in many areas of their North American range (Page and Burr 1991). A variety of factors including deforestation, agriculture, urban development, coal mining, golf course development, pollution and introduced species have been implicated in these declines (Trautman 1981; McKee and Parker 1982; Becker 1983; Meade et al. 1986; Goforth 2000; Lyons et al. 2000). In Ontario, redside dace are subject to numerous threats that vary across its range. Parker et al. (1988) suggested that siltation and removal of bank cover in urban areas were important limiting factors. None of these threats has been empirically demonstrated, but there is sufficient evidence to identify probable cause and effect in some instances.

Given that more than 80% of Canada’s redside dace populations are found in the ‘Golden Horseshoe Region’ of Ontario, urban development represents the most immediate threat to the species in Canada. Several populations have been lost or remain only in headwater areas as urban development proceeds. About one-half of the extant redside dace locations are in, or adjacent to, areas expected to be developed over the next 15 years. The human population of the Greater Toronto Area is expected to increase by 1.3 million over the next 15 years (Federation of Ontario Naturalists 2001). In the Golden Horseshoe Region, the population is expected to increase by almost 4 million people by 2031 (MPIR 2004). The healthiest remaining populations are near the current extent of urban development, but are found in watersheds that are relatively undisturbed.

The underlying mechanisms associated with urban development that negatively impact redside dace are poorly understood, but likely relate to numerous factors. An important overriding factor may be changes to in-stream channel structure that result in widening of the channel and reductions in pool depth. Such changes are often associated with hydrological changes and increases in peak discharges that occur when the landscape is cleared of vegetation and hardened (OMNR 2001). These changes also contribute to siltation that may affect redside dace feeding success through reductions in water clarity, particularly during the construction phase.

Several studies have shown that the quality of streams and their biota can be negatively affected when impervious cover (e.g., roads, houses, parking lots) exceeds 10% of a stream’s catchment area (Booth and Jackson 1997, Wang et al. 2001, Environment Canada 2004, Stanfield et al. 2004). A study of streams in the Lake Ontario basin demonstrated that salmonid species only occurred in streams with a catchment that was less than 10% impervious cover (Stanfield et al. 2004). Wang et al. (2001) concluded that levels of connected imperviousness above 12% are associated with sharp declines in fish species richness, bank erosion and base flow. While such detailed landscape-based analysis has not yet been conducted for redside dace habitats in Ontario, a preliminary analysis by Parish (2004) also found that redside dace preferred stream channels that are not heavily influenced by urban drainage.

Direct changes to channel structure, through channelization that often occurs in urban areas, may also widen channels, reduce pool depth, increase peak discharges, and increase siltation. Removal of riparian vegetation, an important source of cover, would directly affect the production of terrestrial insects required by redside dace during a large portion of the year. Daniels and Wisniewski (1994) suggested that extensive alteration of riparian vegetation may be more important than instream habitat alterations in causing declines of redside dace populations. In-stream barriers and weirs may affect redside dace access to spawning areas and could be detrimental if metapopulation dynamics are important to redside dace populations. A rise in stream temperature is often associated with clearing of forests (Johnson and Jones 2000) and urban development (Leopold 1968), and may be detrimental to redside dace, particularly if the increase is sudden. Other developments may contribute to reductions in groundwater inputs that are important in regulating summer temperatures and base flows in streams.  Groundwater is probably also important to maintain winter habitat. Although the tolerance of redside dace to pollutants is unknown, urban developments pose the risk of exposing local populations to household chemicals and storm water run-off. Nutrients, metals, chlorides and bacteria counts were elevated in two Credit River tributaries (Fletcher’s and Silver creeks) where redside dace have disappeared or declined due primarily to loadings from urban runoff (CVC 2002).

Despite the fact that urban development is a primary factor affecting redside dace populations in Canada, declines in redside dace distribution and abundance have also been observed in agricultural settings (e.g., Saugeen River and Irvine Creek). While low intensity operations (e.g., hayfields) may not pose a problem, intensive agriculture (e.g., row cropping and intensive grazing) presents several threats to redside dace populations. Some of the factors that may affect redside dace are similar to those found in urban settings; however, specific mechanisms are poorly understood. Removal of riparian vegetation to increase crop production or allowing livestock access to streams can contribute to siltation, changes in channel structure and deplete supplies of terrestrial insect food. Some streams formerly occupied by redside dace and tributaries to streams currently occupied, have been channelized and converted to municipal drains. The extensive use of tile drains also increases flows after storm events and can serve as a conduit for sediment (Culley et al. 1983). Agricultural landscapes also provide the opportunity for episodic or chronic pollution events associated with the use of pesticides and fertilizers. A recent manure spill in Irvine Creek killed all fishes along several kilometres of stream, but no redside dace were identified (Coulson pers. comm. 1999).

The decline of redside dace in Mountsberg Creek and Spencer Creek followed the construction of reservoirs near the headwaters. These have altered the thermal regime and may have made temperatures unsuitable for redside dace (Featherstone pers. comm. 2000). Potential predators such as northern pike, largemouth bass (Micropterus salmoides) and black crappie were also newly captured in the creeks and may have had a deleterious effect on the redside dace.

The impacts of introduced species on redside dace have not been specifically studied, but declines in redside dace populations have been observed in Spencer Creek concomitant with the introduction of potential cyprinid competitors, such as rosyface shiners (Notropis rubellus), and predatory northern pike (Holm 1999). Resident brown trout and migratory rainbow trout have been introduced into several Toronto area streams with redside dace populations and redside dace occasionally naturally co-occur with brook trout. There is evidence that redside dace have co-existed with introduced salmonids in several Toronto area streams, but specific studies on the interactions between these species are required. Lyons et al. (2000) noted that redside dace disappeared in two Wisconsin streams after the introduction of brown trout, but no cause and effect relationship was established. Redside dace may be more susceptible to the impacts of introduced species when stream systems are affected by multiple stresses.

Activities associated with the extraction of aggregates may result in reduced base flows and increased stream temperatures (OMNR 2001). Redside dace disappeared in a Kentucky stream that was impacted by gravel extraction, septic seepage and agricultural activities (Meade et al. 1986). Similarly, withdrawals of surface water and groundwater (e.g., golf ourses; agricultural irrigation) in watersheds with redside dace populations may reduce flows to unacceptable levels and result in increased stream temperatures. The impacts of such extraction and withdrawal activities on redside dace populations have not been investigated but are expected to be negative.

The impact of bait harvest on populations of redside dace has not been studied. Populations restricted to a small length of stream may be particularly vulnerable to exploitation through bait harvesting. Redside dace are very vulnerable to seine nets, the most common gear used by baitfish harvesters in southern Ontario streams. However, due to restricted access, most streams are only harvested at road crossings. Redside dace are not a legal baitfish in Ontario (they are protected under the Ontario Fisheries Regulations), but there is potential for incidental harvest.

In Ontario, redside dace appear to achieve their highest abundance in open streams with riparian zones consisting of grasses, forbs and low shrubs. These habitats may be maintained by the presence of wetlands, land clearing, spring flooding, ice scour and beaver activity. Treed areas with complete canopy closure do not appear to provide optimal habitat. Succession to tree species and canopy closure in riparian areas may similarly reduce the quality of redside dace habitat. Andersen (2002) found that areas that supported redside dace in the 1950s when they were under agricultural use, did not support redside dace when they had reverted to forest. Current streamside restoration efforts on redside dace streams in Ontario are using native grasses and shrubs to revegetate riparian areas.

The impacts of climate change effects are difficult to predict. Climate change is expected to 1) have no effect, 2) reduce stream flows and increase stream temperatures or 3) increase the frequency of flooding events in southern Ontario within the range of redside dace (IPCC 2001). The last two changes are expected to be detrimental to populations of redside dace, although, if properly managed, higher rates of precipitation could increase available habitat. Although climate change may make conditions more suitable for redside dace in more northern portions of the province, the potential for colonizing new areas is low.

While it is unlikely that scientific collections have had a major impact on redside dace populations in Canada (few have been collected), collecting should be viewed as a potential threat. This is particularly true for populations that currently occupy a reduced length of stream and may be restricted to a small number of pools. Although redside dace are normally released when they are captured during monitoring projects, there are examples of studies where relatively large numbers of specimens have been collected. The OMNR generally prohibits lethal sampling when Scientific Collector’s Permits are issued.