. The Canadian field-naturalist. 218 The Canadian Field-Naturalist Vol. 112. Figure 2. Typical riffle habitat occupied by Stonecats in the Little Saskatchewan River at Rivers, Manitoba (see site 19, Table 1). Huron in wave-exposed rocky areas (Trautman 1981), the mainstem of the Mississippi River (Robison and Buchanan 1985) and in the Canadian section of the Red River (Stewart and Lindsey 1970). In Manitoba, the first authenticated collection of the Stonecat in the Hudson Bay drainage was made in 1969, with nine specimens taken from the Red River just south of Winnipeg (Stewart and Lindsey 197
. The Canadian field-naturalist. 218 The Canadian Field-Naturalist Vol. 112. Figure 2. Typical riffle habitat occupied by Stonecats in the Little Saskatchewan River at Rivers, Manitoba (see site 19, Table 1). Huron in wave-exposed rocky areas (Trautman 1981), the mainstem of the Mississippi River (Robison and Buchanan 1985) and in the Canadian section of the Red River (Stewart and Lindsey 1970). In Manitoba, the first authenticated collection of the Stonecat in the Hudson Bay drainage was made in 1969, with nine specimens taken from the Red River just south of Winnipeg (Stewart and Lindsey 1970). Those authors offered two hypotheses with respect to the timing of the invasion of the Stonecat into the drainage. The first was that the species moved into glacial Lake Agassiz while the latter was discharging via the Warren River outlet (now occupied by the Minnesota River); the second, that Stonecats moved into the watershed more recently from the Minnesota River. By 1983, the Stonecat had been reported in the Assiniboine River west to the city of Brandon (Stewart et al. 1985). Grossman (1991) considered its presence in Manitoba to be the result of either natural invasion or unintentional introduction. In 1989 and 1990, extensive surveys of the Red and Assiniboine river watersheds were conducted to: (1) determine, as accurately as possible, the pre- sent distribution of the Stonecat in Manitoba; (2) estimate its time of arrival in the Hudson Bay drainage and postulate a probable route of entry; and (3) suggest possible avenues for future dispersal in the drainage. Methods and Materials Road-accessible collection sites were selected from a 1:500 000 scale section map produced by the Province of Manitoba, Surveys and Mapping Branch. Latitudes and longitudes were recorded for each site using the same map. A Smith-Root Model 12 Electrofisher was used to collect fish in shallow, riffle habitats. Voltage and pulse rate were varied as required to immobilize small fish effective
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