CREATION AND MAINTENANCE OF HABITAT DOWNSTREAM FROM A WEIR FOR THE GREENSIDE DARTER, ETHEOSTOMA BLENNIOIDES - A RARE FISH IN CANADA

The biology, microhabitat use and migratory behaviour of the greenside darter, Etheostoma blennioides, was studied at the Mannheim Weir on t he Grand River, Ontario during the summer of 1995 and 1996. Officially listed as vulnerable in Canada, greenside darters reached maturity at age 1 and lived up to 4 years. They were found in riffle habitats tha t consisted of cobble and loose boulders, with large mats of Cladophor a. This type of unembedded substrate is uncommon in the Grand River wa tershed. However, local abundance of greenside darters immediately dow nstream from the Mannheim Weir was likely due to high water velocities from weir discharge, freshets and ice scour which help maintain unemb edded riffle areas. Trap data indicated that greenside darters tempora lly partition this habitat with the stonecat, Noturus flavus. Other da rter species were not commonly found in areas with greenside darters, whose depth selection and habitat choices were influenced by predators and morphology. Denil fishways at the Mannheim Weir rarely passed gre enside darters due to prohibitively high water velocities and exclusio n by larger fish.