Redbreast sunfish (Lepomis auritus) COSEWIC assessment and status report: chapter 8

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Limiting Factors and Threats

There is little information in the literature concerning limiting factors for this species, which appears to be adaptable to a wide range of ecological conditions. Although they prefer clean, clear waters they have been reported to do well in water of pH 4.8 to 8.4, salinities of up to 8 per thousand, and ambient water temperature of up to 37º C (Carlander 1977). Houston (1989) suggested that they tend to do better in uncrowded conditions with few predators.

The most obvious potential threats for aquatic species in New Brunswick are shoreline development (Table 2) for cottages and homes, forestry and agricultural activities, and stream alterations. Though habitat may be directly affected by shoreline alteration or breaches of forestry buffers, the greater impacts would likely be reflected in water quality.

To assess the level of threat to the species, two approaches were combined. First, a relative ranking of the level of habitat pressure was derived from an analysis of orthophotos of the lands surrounding the lakes and the stretches of river from which redbreast sunfish has been recorded.

Second, water quality data or indices were examined, particularly in light of surrounding land use pressures. Water quality information was available for Yoho Lake through the monitoring program conducted by the New Brunswick Department of Environment from 1975 to 1991, in response to the development boom on the lake (Table 3). The following parametres were included: pH, alkalinity, conductivity, hardness, bacterial counts, productivity, total phosphorus, sodium, potassium, nitrates and nitrites, suspended solids and several metals (Fe, Mn, Cu, Pb, Zn, Cd, Al) (NB Department of Environment 1991). In addition, temperature and dissolved profiles were compared at four intervals during this study.

Water quality information for a number of New Brunswick rivers has also recently been made available, with reporting in two forms. Weighted averages of samples were used to assign sites throughout the watershed to one of five categories (excellent, good, fair, marginal or poor), defined in relation to the Canadian Council of Ministers of the Environment (CCME) Water Quality Index. In addition, four key indicators (dissolved oxygen, E. coli, nitrate and pH) were calculated for each watershed as the percent of total samples meeting the CCME standards. Results were available for three of the rivers with records of redbreast sunfish: the Saint John, Canaan and Kennebecasis rivers.

Limiting factors/threats – lakes 

Of the five New Brunswick lakes with recent records of redbreast sunfish, Yoho Lake is unique in the extent of shoreline development, with almost the entire periphery devoted to cottages or year-round residences (Table 2a). No significant trends were detected in water quality over time, though slight increases were noted in total phosphorus (Table 3). While it is not possible to determine if there have been declines in the redbreast sunfish population over this period, the abundance estimates from Gautreau and Curry (2006) nonetheless indicate a sizable population of the species within the lake.

None of the four other lakes included in the analysis approached the same level of development pressure (Table 2a). Given the repeated sampling success or reports of sizable populations, there appears to be little evidence of appreciable threats to these populations.

Limiting factors/threats – rivers and streams 

In the case of the rivers and streams with redbreast sunfish records, a 4 km stretch of shoreline was characterized, consisting of 2 km upstream and 2 km downstream of the presumed location of collection (Table 2b). However, almost the entire length of Rusagonis Stream was characterized, while the Kennebecasis River was omitted, as a result of lack of a specific location for the collections on these two watercourses. The Rusagonis Stream was identified as the most susceptible or altered of the watercourses examined. The Kennebecasis is likely to have also been identified as vulnerable due to the development pressures and agricultural activity along its valley.

Water quality surveys conducted on the Saint John River between 2003 – 2006 indicate that of the 30 sites monitored, water quality in 25 was excellent to good, four were fair, and only one, downstream of Fredericton, was marginal. Although all indicators including dissolved oxygen and nitrate levels were acceptable, E. coli and pH levels remained outside the accepted guidelines (New Brunswick Department of Environment 2007). Fair and marginal water quality may be due to industrial discharges, which are located at points throughout the watershed. These include a number of food processing plants and pulp and paper mills, numerous non-municipal and municipal discharges as well as runoff from urban development. The removal of riparian vegetation (which leads to increased erosion) may have also contributed.

Similar surveys were conducted in the Canaan and Kennebecasis rivers from 1996 – 2006. Of 28 sites monitored in the Kennebecasis, water quality in 23 of the sites was excellent or good, and four were only fair due to high E. coli concentrations linked to the removal of riparian vegetation, and nutrient loads from agricultural and municipal operations (New Brunswick Department of Environment 2007). Of the 25 sites monitored in the Canaan River 16 sites were good to excellent and 9 were fair. In this case, E. coli and pH levels of the 9 sites rated fair were considered to be in excess of the guidelines due to the removal of riparian vegetation and agricultural practices related to manure handling and access of livestock to streams (New Brunswick Department of Environment 2007).

In short, though there are few recent data on the redbreast sunfish from the Canaan and Kennebecasis Rivers, the water quality in both systems does not appear to be limiting, except at localized problem areas. The apparently limited movement of the species could make populations in these areas particularly susceptible, though this factor would account for a small percent of the available habitat.

Other limiting factors/threats 

Given that redbreast sunfish is believed to be restricted to southwestern or southern New Brunswick, the only hydroelectric dam on the Saint John River that would have potentially had an impact on the species is the Mactaquac dam, roughly 18 km upstream of Fredericton, completed in 1968. There is no information on the historic distribution of the redbreast sunfish in the Saint John River, just as the current picture is likely incomplete due to the localized nature of the populations. The only recent record is from Gagetown, perhaps 45 km downstream of Fredericton, indicating the persistence, at least, of the species in this watercourse.

It should be noted, however, that the apparently limited dispersal or movement of the redbreast sunfish may also make it less likely to take advantage of additional habitat within the same drainage system and essentially precludes migration between systems.