Mapleleaf mussel (Quadrula quadrula) COSEWIC assessment and status report: chapter 2

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Executive Summary

Species information

The Mapleleaf, Quadrula quadrula, (Rafinesque, 1820) is a freshwater bivalve belonging in the family Unionidae. The shell is thick, quadrate in outline and ranges in colour from yellowish green through light brown to dark brown. Typically the species can be recognized by 2 rows of raised nodules extending in a v-shape from the umbo to the ventral margin. There are occasional deviations from this nodule pattern. Canadian specimens reach 125 mm in length, 100 mm in height and 50 mm in width. Interior of the shell is white with heavy hinge teeth.

Distribution

The type locality is the Ohio River. In the United States this species occurs throughout the Ohio-Mississippi drainages ranging from Texas to Alabama in the south to Minnesota and Pennsylvania in the north.  Its distribution extends into the Great Lakes drainage in Minnesota and Wisconsin to New York and into the Red River drainage in Minnesota and North Dakota. In Canada this species is limited in Manitoba to the Red River and some tributaries, most notably the lower Assiniboine River, and in southern Ontario to larger rivers draining into Lake St. Clair and Lake Erie. 

Habitat

Quadrula quadrula occurs in a variety of habitats ranging from medium to large rivers with slow to moderate current, lakes and reservoirs in mud, sand, or gravel substrates. In Manitoba and Ontario Q. quadrula is most typically recovered from medium to large rivers in firmly packed coarse gravel and sand to firmly packed clay/mud substrate.

Biology

Quadrula quadrula is dioecious with little or no difference in shell morphology of the two sexes. Larvae, called glochidia, are brooded in the gills by the female and are parasitic on catfish species. Known fish hosts are the flathead catfish which does not occur in Canada, and the channel catfish which does occur in Canada. Development on the fish host requires approximately 50-60 days. During this time the larval mussel transforms to a juvenile, then drops off the fish host and grows to adult size and maturity. Like other freshwater mussels, Q. quadrula feeds on algae and bacteria filtered from the water column and substrate.  Quadrula quadrula is a long-lived species with individuals from Manitoba living up to 64 years and averaging 22 years of age.

Population sizes and trends

Although actual population sizes are estimated to range between 1-4 million in Manitoba, and approximately 5.5 million in Ontario, population densities are generally very low and appear to be in decline. Populations in Manitoba occur only in the Red River and the lower reaches of the Assiniboine and Roseau Rivers. Comparison with historical records of distribution indicates overall that the freshwater mussel fauna in Manitoba is in decline. Where Quadrula quadrula does occur it is never abundant with many fresh empty valves indicating high levels of recent mortalities.

In Ontario Quadrula quadrula populations are restricted to a few rivers draining into Lake Erie and Lake St. Clair.  Reports indicate that the mussel fauna in this region also is in decline with many species considered extirpated from areas they once occupied. Comparison with historical records indicates a reduction in the distribution of this species in Ontario. Recent studies indicate that Q. quadrula is considered to be rare in locations where it does occur and may be in decline, although it does appear to be increasing its distribution within the Sydenham River.

Limiting factors and threats

Like almost all North American freshwater mussels this species is threatened by habitat loss and degradation and the effects of invasive species, particularly the zebra and quagga mussels (Dreissena polymorpha and D. bugensis) in Ontario. In both Manitoba and Ontario Quadrula quadrula occurs in areas that are heavily populated by people and that are affected by industrial and municipal pollution and agricultural runoff.

Special significance of the species

There are 20 recognized species in the genus Quadrula of which 1 species is considered extinct and 4 species are considered endangered in the United States. Quadrula quadrula is the only species of the genus that extends into Canada occurring in Manitoba and southwestern Ontario. Canadian populations occur in the Great Lakes/St. Lawrence watershed (Ontario) and the Hudson Bay watershed (Manitoba). These are continental watersheds that are separate from this species’ main distribution in the Mississippi drainage. These Canadian populations may represent unique genetic and ecological information important in conserving the diversity of the species. 

Existing protection

This species is not specifically protected in Canada.Quadrula quadrula is considered to be stable in some states and critically imperiled in others, but in the majority of jurisdictions the species is unranked or ranks are under review.

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^th 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 (2006)

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 it 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.