Gravel chub (Erimystax x-punctatus) COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

The 1923 Thames River gravel chub collection site was located between the mouth of Hogg Creek and a point on the Thames at Muncey (Holm and Crossman 1986). Habitat at this site was described as clear water, fast currents, substrates comprised of clean sand and gravel and depths up to 1.5 m (Parker et al. 1987). The river width at the capture location in 1923 is unknown. In the mid-1980s, it was 20-30 m wide and 1-3 m in depth with pool and riffle habitats predominating. Substrate material was composed of sand, rock and stone with areas of soft organics and silt. Water was turbid [Secchi disc reading less than 1 m (Parker and McKee 1980; Holm and Crossman 1986)]. Bank cover was minimal and instream vegetation restricted to encrusting and filamentous algae. Water temperatures ranged from 18 to 25°C in July (Holm and Crossman 1986), 21 to 24°C in August (Parker and McKee 1981), and 12 to 15°C in October (Holm and Crossman 1986). In 1958, nine gravel chub were captured while trawling from Lot 16 in Mosa Township to the eastern limit of the Moravian Indian Reserve (Holm and Crossman 1986). No habitat data is available for this capture location.

Elsewhere in North America, gravel chub have been reported as inhabiting clear to moderately turbid streams with permanent flow and well-defined sand, gravel or rocky riffles where the current keeps the river bottom free of unconsolidated silts and clays (Pflieger 1957; Trautman 1981). In Ohio, gravel chub were found in medium to large streams, at depths of 0.3-1.2 m during the summer, and at 0.6-1.8 m during the winter (Trautman 1981). Trautman (1981) reported that the species avoided areas with macrophytes, larger species of algae and aquatic mosses. Presumably these areas would show silt accumulation. In Wisconsin, gravel chub were collected from turbid waters, devoid of aquatic vegetation, over swift gravel riffles 0.3-0.9 m deep, with a channel width of 9-12 m (Becker 1983). Moore and Paden (1950) described its micro-habitat as small cavities beneath rocks in riffle areas where the current is reduced.

Trends

Aquatic habitats within the Canadian range of the gravel chub have undergone considerable historical transformation. Loss of wetlands and riparian vegetation, shoreline alteration, dredging, stream channelization, discharges of toxic chemicals, increased sediment and nutrient loading have been linked to altered composition and lower productivity of regional fish communities (Dextrase et al. 2003; MacLennan et al. 2003; Ryan et al. 2003). During the last targeted gravel chub survey, riffle habitats were present; however, habitats were affected by high levels of turbidity (Holm and Crossman 1986). In August of 2005, secchi disk readings from the Thames River adjacent to Muncey (0.25 m and 0.38 m) indicate continued high levels of turbidity (Marson et al. 2006). Elevated siltation and turbidity in the lower Thames River (Jackson Turbidity Units = 69.5) are primarily the result of agricultural practices in the Thames River watershed (Bailey and Yates 2003). Agriculture represents 78% of land use in the upper watershed and 88% in the lower watershed (Taylor et al. 2004).

Nutrients such as nitrogen and phosphorus enter the Thames River through manure and fertilizer spreading, manure spills, sewage treatment effluent and faulty domestic septic systems (Taylor et al. 2004). Since the 1970s, phosphorus levels at most sites in the watershed have shown a gradual downward trend but remain above the provincial guidelines (30 ug/L) for the protection of aquatic life. Nitrate and chloride levels in the Thames River have increased over the past 30 years (Taylor et al. 2004). High levels of nitrogen and phosphorus can promote algal blooms. Extensive algal coverage would reduce the suitability of affected habitats for gravel chub, and decomposition associated with algal die-offs would reduce dissolved oxygen levels and increase the risk of fish kills (Miltner and Rankin 1998).

In response to these historical and ongoing stresses, species-at-risk recovery strategies are currently being developed and implemented for the Thames River. Actions to protect and improve habitat in the area where gravel chub was formerly known to occur are identified in the Recovery Strategy for Gravel Chub (Erimystax x-punctatus) in Canada (Edwards et al. 2007), and the Thames River Aquatic Ecosystem Recovery Strategy (TRRT 2005). The Thames River Aquatic Ecosystem Recovery Strategy addresses the recovery needs of the 24 aquatic or semi-aquatic COSEWIC-listed species (7 mussels, 6 reptiles, 11 fishes, including the gravel chub) that either historically inhabited or currently inhabit the Thames River. Habitat improvement goals identified for the Thames River of benefit to gravel chub include reductions in sediment, nutrient and toxic chemical loadings.

Protection/ownership

The Canadian Environmental Assessment Act, Canadian Environmental Protection Act, Federal Fisheries Act, Canada Water Act, Ontario Environmental Protection Act, Ontario Environmental Assessment Act, Ontario Planning Act and Ontario Water Resources Act, and Species at Risk Act may offer some protection through protection of wetlands and habitats of other species.

Most of the land along the lower Thames River is privately owned. Lands adjacent to past gravel chub collection sites include the following First Nation territories: Muncey I.R. 1, Munsee-Delaware First Nation; Oneida I.R. 41, Onyota’a:ka First Nation; and Caradoc I.R. 42, Chippewa of the Thames First Nation.

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