Greenside darter (Etheostoma blennioides) COSEWIC assessment and status report: chapter 2

Executive Summary

Greenside darter
Etheostoma blennioides

Species information

The greenside darter is one of seven members of the genus Etheostoma found in Canada. It is the largest member of the genus, reaching lengths of up to 170 millimetres (mm), but the average length in Canada is 76 mm. The greenside darter can be distinguished from other members of the genus in Canada by its green colouration, the fusion of the upper lip to the side of the head, and the presence of large V-shaped marks on the side of the body.

Distribution

The greenside darter occurs in drainages of the lower Great Lakes and the Mississippi River from New York and Maryland west to eastern Kansas and Oklahoma, and from Ontario south to Georgia, Alabama and Arkansas. The species is also found in the Mohawk, Susquehanna and Potomac River drainages of the Atlantic Slope from New York south to Virginia. It is only known in Canada from southwestern Ontario where it occurs in tributaries to Lake Huron, Lake St. Clair, and Lake Erie. Since the status of this species was last reviewed in 1990, the greenside darter has been found to be extant at most historical locations (within four river systems and Lake St. Clair) and has appeared to have expanded its range in the Ausable and Sydenham rivers. It has also been found in five new watersheds as a result of range expansion.

Habitat

The greenside darter is widely distributed in a variety of habitats, but is primarily found in creeks and small to medium rivers with abundant gravel and rubble riffles. It is often associated with vegetation, particularly filamentous green algae in the genus Cladophora.

It also inhabits the shorelines of some large lakes such as Lake St. Clair in Ontario and the Ohio waters of Lake Erie. Greenside darter normally spawn in swift, rubble-covered riffles where larger rocks are covered with growths of the filamentous algae Cladophora spp., or the moss Fontinalis spp. Although urban development and agricultural activities have impacted aquatic habitats and have probably contributed to the decline of other aquatic species at risk in watersheds containing greenside darter, populations have appeared to remain stable or have expanded their range in the face of these changes. The colonization of five new watersheds by the greenside darter over the last 15 years has resulted in an increase in available habitat.

Biology

The greenside darter is relatively short-lived, having a typical life span of 3 years. Individuals of both sexes mature in the spring following their first growing season at age 1. Greenside darter spawn in the spring when water temperatures reach 10.6°C. Spawning occurs in March and April in the southern part of their range, while in the north, spawning is initiated in April and can continue into June. The adhesive eggs are normally laid on filamentous algae, or on an aquatic moss close to the point of attachment to the rock. Eggs hatch in 18-20 days at 13-15°C and larvae transform into the juvenile stage in late June and July. Greenside darter are benthic (bottom dwelling) insectivores that feed primarily on the larvae of midges (Chironomidae), blackflies (Simuliidae) and mayflies (Ephemeroptera). A broad range of food items has been reported, suggesting that the greenside darter is an opportunistic feeder. The greenside darter is less tolerant of high water temperatures and low summer oxygen levels than other darters with which they commonly co-occur. The rapid spread of greenside darter within the Potomac River in the United States and within the Grand River in Ontario provides evidence of its dispersal abilities.

Population sizes and trends

Recent surveys have shown that the greenside darter is widespread and abundant in the Ausable, Sydenham and Thames rivers. Sampling in Lake St. Clair in the 1990s has revealed their widespread presence in the lake and perhaps an increase in abundance. The greenside darter was introduced to the Grand River watershed prior to 1990 and, in 15 years, has become established in more than 200 stream kilometres (km) where it is often abundant. There is no information on the abundance of greenside darter in the Bayfield River, Big Creek, Big Otter Creek, Detroit River or Pefferlaw Brook. Rescue of greenside darter populations in Canada is possible from Michigan populations.

Limiting factors and threats

There are several potential threats to greenside darter populations in Canada, but none appear to be imminent or currently having a significant impact on populations. Potential threats include: impoundments; sediment and nutrient inputs associated with agricultural activities; contaminants associated with industrial activity and agricultural runoff; rapid urban growth in the Grand and Thames river watersheds; and predation and competition from the introduced round goby (Neogobius melanostomus).

Special significance of the species

The greenside darter likely plays an important role in converting benthic energy in lotic ecosystems. It also serves as a larval host for one endangered mussel species in Canada. The greenside darter is of considerable interest for scientific studies and may be of interest as an aquarium fish.

Existing protection and other status designations

Assessed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 1990 as special concern, the greenside darter is not protected by any federal or provincial species at risk legislation in Canada. The greenside darter is considered globally secure (G5), and is ranked as secure (S4 or S5) in most American states where it occurs.

COSEWIC History

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC Membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.

Definitions

Wildlife Species
A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years.

Extinct (X)
A wildlife species that no longer exists.

Extirpated (XT)
A wildlife species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)
A wildlife species facing imminent extirpation or extinction.

Threatened (T)
A wildlife species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)Footnotea
A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats.

Not at Risk (NAR)Footnoteb
A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.

Data Deficient (DD)Footnotec
A category that applies when the available information is insufficient (a) to resolve a species' eligibility for assessment or (b) to permit an assessment of the species' risk of extinction.

 

Canadian Wildlife Service

The Canadian Wildlife Service, Environment Canada, provides full administrative and financial support to the COSEWIC Secretariat.

 

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