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

Population Size and Trends

Recent paleolimnological evidence suggests that the native lakes began to acidify as early as the 1940's (Dixit et al. 1996). In 1951 the Ontario government began to monitor the native Aurora Trout populations and by the late 1950's the populations had noticeably declined. By 1967 the Aurora Trout had disappeared from its native range. The other fish species in the native lakes were also extirpated.

Since 1958 the Aurora Trout has been maintained artificially in OMNR fish culture facilities. The lineage of all Aurora Trout in existence today can be traced back to a 1958 spawn collection. That year 3644 eggs were collected from one Whitepine Lake female and two Whirligig Lake females (Patrick and Graf 1961). The eggs from each female were mixed with the sperm from two males. Thus, the founding population size was nine individuals (3 females, 6 males) and may have been as few as six if all males did not contribute to fertilization. Currently in any one year 500-1000 fish are kept as brood stock in the Hill's Lake Fish Culture Station. The brood stock is maintained by biannual egg collections in Alexander Lake (25 000-40 000 eggs/year). The total number of eggs collected per year by the captive breeding program, including those from Alexander Lake, is 50 000-150 000.

Successful reproduction has occurred annually in Whirligig Lake since it was restocked with hatchery-reared Aurora Trout in 1990 and in Whitepine Lake since 1994 following stocking that was done in 1991 and 1994. The biomass of Aurora Trout in Whirligig Lake quickly increased after stocking to levels comparable to that of Brook Trout populations in unacidified lakes and growth rates of the fish are similar to pre-acidification (Snucins et al. 1995) (Table 1). Natural reproduction was also documented in Southeast Campcot Lake in 1991 and in Northeast Campcot Lake in 1994. The abundance of those populations appeared to decline during the late 1990’s and by 2001 they were extirpated. There is no evidence of successful reproduction in Alexander Lake, the egg source for hatchery brood stock, or in any of the 9 lakes that are used for the limited recreational fishery.

 

Table 1: Estimated Number (N) and Biomass (B) of Stocked and Natural Aurora Trout in Whirligig Lake (Numbers in parentheses are lower and upper 95% confidence intervals)
YearStocked
N
Stocked
B (kg/ha)
Natural
N
Natural
B (kg/ha)
1990209 (151-301)6.7 (4.8-9.6)00
1991307 (173-463)17.2 (9.7-26.0)00
1993156 (108-236)11.3 (7.8-17.1)300 (229-403)4.5 (3.4-6.0)