Greenside darter (Etheostoma blennioides) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

Search effort

No targeted surveys have been conducted for greenside darter in Canada, although several recent surveys have targeted areas where fish species at risk are known to occur. Many greenside darter records are from general stream inventory work or surveys for other purposes. Throughout most of the greenside darter’s Canadian range, pre-1970 sampling effort was sparse and was conducted with seine nets and minnow traps. During the 1970s, the Ontario Ministry of Natural Resources (OMNR) conducted stream surveys, which included systematic fish sampling using a variety of gear types (including backpack electrofishing) throughout most streams, rivers and their major tributaries. The OMNR conducted a standard nearshore seining program along the south shore of Lake St. Clair from 1979 to 1981 and from 1990 to 1996. Such surveys covered most of southwestern Ontario, including the areas into which it has subsequently expanded. Although not specifically directed to any one species, greenside darters were recorded when present (A. Dextrase unpubl. data). Over the last 10 years, specific surveys have been conducted using a variety of gear types by Conservation Authorities, Fisheries and Oceans Canada, the Ontario Ministry of Natural Resources, and the Royal Ontario Museum, targeting historic locations and potential habitats for species at risk in the Ausable River, Bayfield River, Big Creek, Big Otter Creek, Detroit River, Grand River, St. Clair River, Sydenham River, and Thames River watersheds. Similar surveys have also been conducted in Lake Erie (Holiday Beach, Long Point, Pelee Island, Point Pelee, Port Burwell, Rondeau Bay) and Lake St. Clair. While these surveys have not provided complete coverage within the range of the greenside darter, they have added greatly to our knowledge of its distribution. Since the late 1990s, Conservation Authorities have conducted systematic fish sampling of agricultural drains in most southwestern Ontario watersheds as part of a drain classification project. Many of these drains are natural or semi-natural watercourses and this work has provided valuable information on the distribution of fishes in the smaller tributaries of many watersheds. In addition to the surveys described above, greenside darter records have been contributed by government and conservation authority staff, consultants and students who have conducted sampling for other purposes. There are few sampling locations where similar gear and effort have been used through time to allow an analysis of population trends. Poos (2004) found that backpack electrofishers were more efficient for detection and capture of greenside darter than seine nets.

Abundance

There are no estimates of absolute abundance for greenside darter populations in Canada. Given the number of locations at which the greenside darter is found, and its apparent abundance at some sites (e.g., average of 65 per site at 62 sites in the Sydenham River), there are likely more than 10,000 individuals in Canada. Recent survey efforts in some watersheds can be used to make some general statements regarding relative abundance.

Ausable River - The greenside darter was not discovered in the Ausable River until 1974. It is not clear if it was always present in the watershed because of limited sampling prior to the 1970s. Dalton (1991) raised concerns regarding the state of populations in the Ausable River watershed given the turbidity of the system and speculated that the species may be extirpated from the river. During a survey of 25 sites in 2002, the greenside darter was found at over half (13) of the sites surveyed with as many as 71 individuals captured at a single site (Dextrase et al. 2003). Species at risk surveys in 2004 captured greenside darter at 18 of 19 sites along the mainstem of the Ausable and Little Ausable rivers (Stewart and Veliz 2004). The greenside darter ranked third in abundance out of the 50 species encountered in the survey. Stewart and Veliz (2004) concluded that greenside darter populations in the Ausable River basin were abundant and stable.

Sydenham River - The greenside darter was first discovered in the East Sydenham River near Strathroy in 1927 (Dextrase et al. 2001). Sampling in the 1970s revealed that the species was also present in Bear Creek in the North Sydenham drainage. Sampling conducted in 1997 captured the greenside darter throughout much of the East Sydenham River from Strathroy downstream to Wallaceburg, as well as at historical sites in Bear Creek. Substantial numbers were captured at some of the sites (e.g., 46 and 62 individuals at two sites) (Holm and Boehm 1998a). The greenside darter was the tenth most numerous and eighth most frequently encountered species of the 52 fish species found during systematic sampling of the Sydenham River watershed in 1997 (Holm and Boehm 1998a). It was captured at 11 of 23 sites with an average of 14 individuals per capture site. More recently, Poos (2004) conducted systematic sampling in 2002 and 2003 at 100 sites (including 25 sites that were sampled in both years) and captured greenside darter at 62 of these sites. The greenside darter was the third most numerous and eighth most frequently encountered species of 67 fishes, with an average of 65 individuals per capture site (M. Poos, University of Toronto, Toronto, Ontario, unpubl. data). Dalton (1991) suggested that numbers of greenside darter may be reduced in the Sydenham River; however, recent survey work suggests that the species is widespread and abundant in this watershed.

Lake St. Clair - There are few records of greenside darter from Lake St. Clair. Dalton (1991) reported only one record from the lake from 1959. A nearshore seining program was conducted by the Ontario Ministry of Natural Resources from 1979 to 1981, and from 1990 to 1996, along the south shore of Lake St. Clair (M. Belore, pers. comm. 2005). No greenside darter were captured from 1979 to 1981, but 48 were captured (including six young-of-the-year) at four different locations in 5 of 7 years during the 1990-1996 sampling period. This coincides with the changed habitat conditions associated with the zebra mussel invasion (see Habitat Trends above).

Thames River - The greenside darter was first recorded in the Thames River in 1884, and there are now more than 500 records for this species in the watershed (Cudmore et al. 2004). Sampling conducted primarily in agricultural drains from 1999 to 2002, found greenside darter at 52 of 236 sample sites throughout the Thames River watershed. The greenside darter appears to be abundant throughout the Thames River’s main branches, and most of the tributaries that have been sampled (Cudmore et al. 2004). Dalton (1991) suggested that numbers of greenside darter may be reduced in the Thames River; however, recent survey work suggests that the species is present at almost all of the historical locations in the watershed and that it has remained abundant under current conditions. It may be limited by the high turbidity in the lower end of the river (Cudmore et al. 2004).

Grand River - The greenside darter was first captured in the Grand River watershed in 1990, from the Speed River near its confluence with the Eramosa River in Guelph (Fig. 5). Significant fish sampling was conducted in the watershed prior to 1990, including significant sampling in the area of first capture during the 1970s and 1980s (Fig. 5); therefore, it is highly unlikely that this distinctive species was overlooked in previous surveys. The introduction pathway for greenside darter into the Grand River watershed is not known. Given its first appearance upstream in the northeastern portion of the watershed (separated from Lake Erie by several dams), it is likely that the introduction was human-mediated as opposed to natural upstream invasive movements or stream capture from the adjacent Thames River watershed. The subsequent downstream and upstream colonization of the watershed has been rapid and was described by Bunt et al. (1998) as a “localized population explosion”. In 15 years, the greenside darter has become established in more than 200 stream km. Their current upstream distribution along the Conestogo and Grand rivers ends at the Conestogo Lake dam and Elora Gorge, respectively. Three dams on the main stem of the Grand River are equipped with fishways. Bunt et al. (1998) demonstrated that greenside darter were able to move upstream through a Denil fishway at one of these dams when trash racks had not been properly maintained. Greenside darter have also been found upstream of barriers not equipped with fishways in the Speed River (Reid 2004) and MacKenzie Creek (S. Reid, pers. comm. 2005). The greenside darter is an abundant riffle-dwelling darter where it occurs in the Grand River (Bunt et al. 1998; Holm and Boehm 1998b). Portt et al. (2004) speculated that the introduction of the greenside darter is unlikely to alter the overall distribution of other darters in the Grand River (based on their co-occurrence in adjacent watersheds), although some changes in abundance and micro-habitat use may occur.

There is no information available with respect to abundance of greenside darter populations in the Bayfield River, Big Creek, Big Otter Creek, Detroit River and Pefferlaw Brook. The Pefferlaw Brook population is considered to have been the result of a human introduction; thus it is not considered in the assessment. The Grand River population was included in the assessment as it is uncertain whether or not it was introduced there, or was the result of a range expansion.

Fluctuations and trends

There is not sufficient information available to assess population trends other than in a very general sense. The greenside darter remains a widespread and abundant species in the Ausable River, Sydenham River and Thames River. Its range, and presumably its abundance, appear to have increased in the Ausable and Sydenham watersheds. Abundance may have also increased in Lake St. Clair. The species is still present in Big Creek, but there is no information regarding population trends. The total Canadian population of greenside darter has also increased through the recent colonization of the Bayfield River, Big Otter Creek, Detroit River, Grand River and Pefferlaw Brook.

Rescue effect

The rapid establishment and spread of the greenside darter in the Grand River system demonstrates the species’ ability to colonize suitable habitat. A similar rapid range extension was recently documented in the Susquehanna River in Pennsylvania and Maryland (Neely and George 2006).

The greenside darter is present in four American states adjacent to its Canadian range. It is considered common in Michigan (S4) (NatureServe 2006) where it occurs in the southeastern portion of the Lower Peninsula. Populations are present in tributaries to the St. Clair River, Lake St. Clair and western Lake Erie as well as in the Detroit River (Bailey et al. 2004), providing possible sources of rescue for Canadian populations. The greenside darter was found in the Canadian portion of the Detroit River for the first time in 1995, and these fish may have originated from the Michigan side of the river (see Canadian range above). Although the greenside darter is not ranked in Ohio (SNR), it is a widespread species in the state (Trautman 1981), and was collected at over 2,000 sites from 421 Ohio streams between 1979 and 1995 (Sanders et al. 1999). Ohio fish would have to traverse the waters of Lake Erie to colonize Ontario streams. Although the greenside darter was once common around the western islands and south shore of the Ohio waters of Lake Erie, its abundance has declined in these areas (Van Meter and Trautman 1970; Trautman 1981). The greenside darter is common in Pennsylvania (S5) (NatureServe 2006) and is one of the most common darters in western Pennsylvania (Cooper 1983), but only a small portion of the state abuts the southern shore of Lake Erie. No greenside darter have been collected from the Canadian waters of Lake Erie, so it seems unlikely that populations from Ohio or Pennsylvania would rescue Canadian populations. The greenside darter is less common in New York (S3) (NatureServe 2006) and is sparsely distributed in tributaries to the Niagara River near the Canadian border (Smith 1985). No greenside darter have been found in Canadian tributaries to the Niagara River (A. Yagi, pers. comm. 2005), suggesting that rescue from New York populations is also unlikely. 

Page details

Date modified: