Lake Winnipeg Physa Snail

Taxonomy
Scientists believe that the Lake Winnipeg Physa Snail is a new species - one that is at risk of disappearing before it has even been given a full scientific name. It belongs to the family Physidae, and is clearly distinct from the three other snails in the same family that also occur in Lake Winnipeg.

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Description
The shell of the Lake Winnipeg Physa Snail is usually less than 11 mm long, globe-shaped, and fragile. The spire (whorls of a spiral shell, excluding the last) is flattened, making the snail appear relatively wide, and the surface of the shell is dull and often pitted. Fresh shells are bluish-grey, and the skin of living snails is light grey and sparsely peppered with black spots.

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Distribution and Population
The Lake Winnipeg Physa Snail has not been formally described yet, so it is not surprising that there is no information published on its distribution. However, it appears to be found only in Lake Winnipeg. Extensive surveys of almost 1000 sites in Manitoba, Ontario, Saskatchewan, North Dakota, and Minnesota, including the adjacent lakes and tributaries of Lake Winnipeg, did not detect the snail anywhere except in Lake Winnipeg.

The distribution of the Lake Winnipeg Physa Snail in Lake Winnipeg is quite patchy. It was found at only 5 of 90 stations surveyed in 2001. The disappearance of the snail from two previously known sites suggests a population decline.

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Habitat
The Lake Winnipeg Physa Snail can be found on algae-coated rocks that are submerged just below the surface in open, wave-swept areas close to the shore of the lake. The lake bottom is usually a mixture of sand, gravel, and rocks, or occasionally limestone shingle. The Lake Winnipeg Physa Snail tends to occur only in sites with a higher number of other snail species. The average site where the Lake Winnipeg Physa Snail was found had 6.2 species of snails, while the overall average for sites with snails was 3.9 species. The Lake Winnipeg Physa Snail also is always found with at least one other species of Physa snail. The snail appears to be sensitive to metal contamination - the water at the sites where it was found had significantly lower levels of cadmium, copper, and lead than the sites where it was absent.

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Biology
The Lake Winnipeg Physa Snail feeds on algae. Other species of Physa snail that occur in Lake Winnipeg spend the winter as adults and then reproduce in June and July of the following year. The shells of these snails are fragile and individuals typically do not survive for more than one year in Lake Winnipeg.

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Threats
The main threats to the Lake Winnipeg Physa Snail are degradation of the shoreline habitat due to cottage development and recreational use, and pollution of the water from agricultural, municipal, logging, and pulp mill activities near the rivers that drain into Lake Winnipeg. Increased shoreline erosion resulting from water level regulation is an additional concern.

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Protection
Species that have been designated at risk by COSEWIC since the Species at Risk Act (SARA) was written must be added to Schedule 1 through a regulatory amendment. Information on this procedure, including the public consultation process, is available on the SARA Public Registry. If Lake Winnipeg Physa Snail is added to Schedule 1, it will benefit from the protections afforded by SARA. More information about SARA, including how it protects individual species, is available in the Species at Risk Act: A Guide.

The Lake Winnipeg Physa Snail is not protected by any provincial legislation, and all sites where it is known to occur are vulnerable to shoreline alteration and recreational use.

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