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Abstract
Potamilus alatus (Pink Heelsplitter) is a rare freshwater mussel in the Ottawa River drainage (Ontario/Québec, Canada), at the northeastern limit of its distribution. There are few historical records, and one old specimen from an uncertain locality. The discovery of the Pink Heelsplitter in the Ottawa River drainage dates from 1863. A few specimens were reported up to 1901, but it was August 2001 before another specimen was found in the Ottawa River, as an empty shell at Upper Duck Island, near Ottawa. From 2001 to 2005, the authors found this freshwater mussel at four localities along the Ottawa River, and two in the tributary South Nation River. Records include 4 living specimens and 12 empty shells, of which 8 were in fresh condition. The Pink Heelsplitter seems to persist sparsely in the Ottawa River, but it may have been extirpated from one of its tributaries (South Nation River) before its discovery due to mortality associated with Dreissena polymorpha (Zebra Mussel).
Introduction
Potamilus alatus (Say) (Pink Heelpsplitter) is a freshwater mussel (Mollusca: Unionidae) considered to be uncommon or rare in Canada, where it has been reported from the provinces of Manitoba, Ontario, and Québec, in large, slow rivers. Fish-linkage studies indicate that in rivers in the United States it uses the Aplodinotus grunniens Rafinesque (Freshwater Drum) as host for the dispersal and development of its morphologically unusual glochidia larvae (Clarke 1981, Watters 1994). It is distributed throughout the Mississippi River drainage and in the St. Lawrence River drainage from Lake Huron to Lake Champlain (Parmelee and Bogan 1998), with the Ottawa River drainage (Fig. 1) being the northeastern extremity of its distributional range.
With a large thin shell and a prominent postero-dorsal "wing," the Pink Heelsplitter became an ideal substrate for attachment by the introduced Dreissena polymorpha (Pallas) (Zebra Mussel). Mortality associated with Zebra Mussels has nearly extirpated Potamilus alatus from the Laurentian Great Lakes (Gillis and Mackie 1994, Nalepa et al. 1996). Lake Erie, whose populations of unionid mussels have basically been wiped out by the Zebra Mussel, may previously have contained the bulk of Canada's Pink Heelsplitter populations. The Pink Heelsplitter is not yet listed as a "species at risk" by the Committee on Endangered Wildlife in Canada (COSEWIC 2009), but in...