Lake whitefish (Coregonus clupeaformis) in Lake Simcoe COSEWIC assessment and status report: chapter 5
Habitat
Habitat requirements
Generally, lake whitefish spend most of the year in deep water areas of lakes moving to shallower water in the early spring as well as during the fall (Scott and Crossman 1973). In Lake Simcoe, adult lake whitefish are associated with the lake bottom and widely distributed throughout the lake, including the open basin, Cook Bay, and Kempenfelt Bay during the winter and spring (MacCrimmon and Skobe 1970). As water temperature increases in the late spring, Lake Simcoe lake whitefish move to the cool deep waters of the lake to depths of 20 to 40 m.
Lake whitefish move into shallow waters during the fall to spawn, usually in November to December in the Great Lakes region and earlier farther north (Scott and Crossman 1973). In Lake Simcoe, lake whitefish first move to spawning shoals in October and remain until early December (Willox 1986; McMurtry 1989; Amtstaetter 1997). Lake whitefish spawn over shoals consisting of boulder, cobble and gravel. Eggs are deposited randomly and settle within the interstitial spaces of the shoals. Spawning takes place over a wide area of Lake Simcoe as indicated by the catch of lake whitefish during the fall on many known spawning shoals. Amtstaetter (1997) reported that ripe Lake Simcoe lake whitefish females were usually present on spawning shoals from mid- to late November at water temperatures ranging from 0.5 to 10°C and were captured in trap nets that were set in approximately 3 m of water.
Lake whitefish eggs hatch in April or May and young fish leave the shallow inshore waters by early summer and move to deeper water (Scott and Crossman 1973). Surface trawls on Lake Simcoe first captured larval lake whitefish when water temperature reached 4°C. Catch sharply declined once water temperature exceeded 9°C and very few fish were caught when temperature reached 14°C (DesJardine 1979). These fish were widely distributed both inshore and offshore over various depths up to 31 m (located 8 km from shore). Juvenile lake whitefish were caught by gillnets in Lake Simcoe, July 2002 at depths of 20-38 m, where temperatures were approximately 9-11°C.
Trends
The decline of lake whitefish has been attributed to nutrient loading and an accelerated eutrophication and its impacts on spawning and hypolimnetic habitat in Lake Simcoe (Evans 1978; Evans et al. 1988; Evans et al. 1996; McMurtry and Amtstaetter 1999). There has been a threefold increase in phosphorus (P) loading from pre-settlement rates which has affected water quality (Johnson and Nicholls 1989). Evans et al. (1996) reported that the volume-weighted temperature-corrected hypolimnetic dissolved oxygen concentration from August 30th to September 19th declined from approximately 4.5 mg/L in 1975 to 2.0 mg/L by 1993. Nicholls (2001) reported that recent analyses of long-term data indicated some improvements in Lake Simcoe water quality. It was noted that the volume-weighted deep-water oxygen depletion rate (normalized to 4°C) has been decreasing since the 1990s, in contrast to the increasing trend observed through the 1980s. However, it was cautioned that oxygen depletion rates are still high and that meeting interim objectives for end-of-summer dissolved oxygen under the Lake Simcoe Environmental Management Strategy (LSEMS) was unlikely.
Lake Simcoe lake whitefish reproduction relies upon the presence of suitable spawning shoal habitat for successful egg incubation and fry emergence. Although degradation of shoal spawning habitat has been noted as a potential factor in the recruitment failure of cold-water fish species in Lake Simcoe (Evans et al. 1988; McMurtry et al. 1997), the actual impact on the hatching success of lake whitefish in Lake Simcoe is unknown. It is unknown whether zebra mussels, introduced in the mid- 1990s, have impacted Lake Simcoe’s shoal spawning habitat.
Protection/ownership
Much of the Lake Simcoe shoreline is privately owned, consisting of year-round residences and summer cottages. There are also numerous marinas, three provincial parks (Sibbald Point, McRae and Mara) and two provincially protected areas: the Holland Marsh Provincial Wildlife Area and the Duclos Point Provincial Nature Reserve also border Lake Simcoe. However, parks and protected areas offer little in the way of direct protection of spawning habitat of Lake Whitefish.
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