Lake Erie watersnake COSEWIC assessment and status report: chapter 2

Executive Summary

Lake Erie Watersnake
Nerodia Sipedon Insularum

Species information

The Lake Erie Watersnake, Nerodia sipedon insularum, is one of two subspecies of the Northern Watersnake, Nerodia sipedon (family Colubridae), found in Canada. Lake Erie Watersnakes range in colour from being regularly patterned with dark dorsal and lateral blotches to a uniform gray (often a drab greenish or brownish) without pattern. The colour of the ventral scales is generally white or yellowish white, often with dark speckling. The Lake Erie Watersnake is moderately heavy-bodied. The head is large and covered with broad, smooth scales and the body scales are “keeled” with a ridge down the middle. The Lake Erie Watersnake is non-venomous but readily bites when handled. Adult males average between 59 and 71 cmmean snout to vent length (SVL) and adult females average between 80 and 88 cm mean SVL.

Distribution

The Lake Erie Watersnake has one of the smallest distributions of any snake in North America. In its Canadian range, the Lake Erie Watersnake is known to occur only on four small islands in the western basin of Lake Erie (East Sister, Hen, Middle, and Pelee Islands). In the United States, the Lake Erie Watersnake occurs in a small shoreline area of the Ohio mainland and on 11 Ohio islands in the western end of Lake Erie.

Habitat

During the active season, the Lake Erie Watersnake occupies rocky or sandy shorelines, and limestone or dolomite shelves and ledges with cracks and varying levels of vegetation. Natural and human-made rock berms are also utilized. The snakes feed in the water but rarely go more than 50 m from shore while foraging. Watersnakes are rarely found more than 100 m inland during the active season and distance travelled inland is dependent on availability of cover and prey, presence of predators, and suitable basking and escape areas. Inland locations are also used by Lake Erie Watersnakes for hibernation. The hibernation sites are usually cavities and crevices, and are typically composed of soil and rock substrates.

Biology

The Lake Erie Watersnake can live up to 12 years in the wild. Females reach sexual maturity at 3 years of age and males mature at 2 years. Courtship involves scramble competition in which several males court one female simultaneously. Some females reproduce annually. Females give birth to live young and litter size averages 23 and is positively related to the female’s size. The Lake Erie Watersnake’s previous prey of logperch (Percinacaprodes) and other darters has been largely replaced with the round goby (Neogobius melanostomus) which has recently invaded Lake Erie.

Population sizes and trends

Lake Erie Watersnakes were reported in great numbers on several islands of western Lake Erie from the early 1800s and up to the early 1960s. Subsequently, populations have decreased sharply throughout their range. The restricted range of the Lake Erie Watersnake on the islands of western Lake Erie and a low rate of inter-island dispersal make populations vulnerable to stochastic events. The growing number of human inhabitants on these islands increases mortality due to roadkill, persecution and increased loss of habitat.

Limiting factors and threats

The Lake Erie Watersnake’s extremely small geographic range, its restriction to islands and its limited population size amplify the threats that are also affecting many other reptiles in Canada. Increasingly, shoreline and inland development on islands for recreation, summer homes, and tourism is destroying and degrading the snakes’ habitat. Although roadkill and predators contribute to watersnake mortality, the main threat to watersnake populations may still be human persecution. Current studies are examining contaminant concentrations and their effects on Lake Erie Watersnakes. Contaminant levels may be an issue for this snake because its diet largely consists of round gobies that feed on filter-feeding Zebra and Quagga mussels (Dreissena polymorpha and Dreissena bugensis, respectively), which occur in the contaminated waters of western Lake Erie.

Special significance of the species

The Lake Erie Watersnake possesses a colour pattern polymorphism that has provided a rare illustration of microevolutionary change involving effects of selection, gene flow, inheritance, and population history. The subspecies displays local adaptations to living in island habitats that have reduced vegetative cover. Hence, it is genetically and ecologically different from the Northern Watersnake (N. s. sipedon).

Existing protection

Globally, NatureServe lists the Lake Erie Watersnake taxon as imperilled (global rank is G5T2). NatureServe lists the Lake Erie Watersnake as imperilled (S2) in Ontario. The IUCN has not evaluated N. s. insularum. In Canada, N. s. insularum was assessed as Endangered by COSEWICin 1991. In Ontario, it is a regulated species under the Ontario Endangered Species Act and is a specially protected reptile under the Ontario Fish and Wildlife Conservation Act. In the United States, this species is listed as Threatened under the Federal List of Endangered and Threatened Wildlife, and Endangered by the state of Ohio and the Ohio Division of Parks and Recreation.

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 5th 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.

Canadian Wildlife Service

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

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