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COSEWIC Assessment and Update Status Report on the Aurora Trout in Canada

Habitat

The two native Aurora Trout lakes are part of a chain of lakes situated on a ridge in Lady Evelyn Smoothwater Provincial Park. They are some of the highest elevation lakes in Ontario. Whirligig Lake (11 ha surface area; maximum depth 9.1 m; Secchi depth 3.3-6.2 m in 1999; 435 m elevation) flows into Whitepine Lake (77 ha surface area; maximum depth 21.3 m; Secchi depth 3.5-6.0 m in 1999; 430 m elevation). The surrounding terrain is hilly and rough, topography typical of the Precambrian Shield. The lakes are 10 km from the nearest road and accessible only by canoe and trail or by aircraft. Their watersheds have low acid-neutralizing capacities and are vulnerable to acidification.

The native lakes are located within the zone affected by acid deposition from Sudbury metal smelters (Neary et al. 1990). Extirpation of the Aurora Trout during the 1960's coincided with acidification of the lakes to about pH 5.0 (Keller 1978), the threshold for Brook Trout survival (Beggs and Gunn 1986). By 1976 the pH of Whitepine Lake was 4.7. During the 1980's water quality remained unsuitable for Aurora Trout survival in their native lakes (Snucins et al. 1988). Following liming in 1989 the pH of Whirligig Lake increased from 4.8 to about 6.5. The pH has subsequently declined and additional limings were necessary in 1993 and 1995 to increase the pH. However, between 1997 and 1999 the pH remained relatively steady at 5.3-5.6. This is close to the natural pH of the lake, as estimated by paleolimnological analysis of sediment cores (Dixit et al. 1996), and is suitable for Aurora Trout reproduction. Whitepine Lake also exhibited some water quality improvement. It's pH increased from 4.9 in the late 1980's to 5.2 by 1993 and 5.3-5.4 by 1999. The pre-industrial pH of Whitepine Lake was 5.4-5.7 (Dixit et al. 1996). The improvement may be due to input of limed water from Whirligig Lake or atmospheric pollution reductions or both.

The other two lakes that had reproducing populations during the 1990’s, Southeast Campcot Lake (35.6 ha, 43 m maximum depth, 6.8 m Secchi depth) and Northeast Campcot Lake (20.8 ha, 28 m maximum depth, 8.3 m Secchi depth), are located in well-buffered watersheds and are not threatened by acidification.

Spawning by Aurora Trout in Whirligig Lake occurs on groundwater seepages over sand, gravel and rock substrate in water 1.2-4.1 m deep at distances of 2-45 m from shore. The spawning sites in the other lakes have not yet been identified.