Hill's pondweed (Potamogeton hillii) COSEWIC assessment and status report: chapter 2

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Executive Summary

Species information

Hill’s pondweed (Potamogeton hillii) is an entirely submerged pondweed, 30-60 cm long with narrow, linear, bristle-tipped leaves 2-6 cm long and 1-2.5 mm wide. Fruit is brown, up to 4 mm long, and borne on a recurved stalk. Its overall appearance is similar to other linear-leaved pondweeds.

Distribution

In Canada, Hill’s pondweed is found mostly on Manitoulin Island and the Bruce Peninsula, Ontario. Additional reports come from Elgin County, Wellington County, and Peel Regional Municipality. In the United States, it has been found in Michigan, Wisconsin, Ohio, New York, Pennsylvania, Connecticut, Massachusetts, and Vermont. Its extent of occurrence in Canada is about 1300 km².

Habitat

Hill’s pondweed is found in cold, clear, calcareous streams, ponds and ditches with an alkalinity of 53.0 to 316.7 mg/l HCO₃, usually where there is dolomitic limestone. Habitat trends are unknown. Five of the 20 extant populations are in protected areas.

Biology

Reproduction occurs both by seed and vegetatively by winter buds. Flowering occurs in July, and seed set occurs August to September. Seeds are water or waterfowl dispersed. Little research has been done on the ecological role of Hill’s pondweed, but it is likely to fill a role similar to that of other pondweeds.

Population sizes and trends

Hill’s pondweed has been reported at 24 sites in Canada; at two of these the species is extirpated. Field visits were made to 20 sites. A species that resembled Hill’s pondweed was found at 12 sites. At seven sites no fruit was found in 2003, which reduced the certainty of identification. A minimum area of occupancy, based only on the sites where fruit was available for positive identification of the species, would total about 25 ha and consist of an estimated 55,000⁺ plants. If identification was correct in all cases, the area of occupancy would be about 27 ha, including supplementary data provided by the Ministry of Natural Resources, Ontario, and the population estimated to comprise approximately 119,600 individuals.

Limiting factors and threats

The main threats to Hill’s pondweed are habitat destruction and degradation.

Special significance of the species

As in the case of other pondweeds, the species likely serves as food for waterfowl and possibly for some mammals. No Aboriginal uses have been recorded in the literature.

Existing protection or other status designations

Hill’s pondweed was designated in 1986 as Special Concern by COSEWIC In Ontario, the species is listed as Threatened under the recently approved Species at Risk list. It is Endangered in Connecticut, Ohio and Pennsylvania, Threatened in Michigan, and of Special Concern in Massachusetts. NatureServe assigns it a global rank of vulnerable (G3).

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 agencies (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 members and the co-chairs of the species specialist and the Aboriginal Traditional Knowledge subcommittees. The Committee meets to consider status reports on candidate species.

Definitions (November 2004)

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 wildlife species for which there is inadequate information to make a direct, or indirect, assessment of its risk of extinction.