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

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COSEWIC
Executive Summary

Aurora Trout
Salvelinus fontinalis timagamiensis

Description

The Aurora Trout is a subspecies of the Brook Trout (Salvelinus fontinalis Mitchill 1815) that is endemic to two small lakes (Whitepine and Whirligig) located about 110 km north of Sudbury, Ontario. Aurora Trout are distinguished from other Brook Trout mainly in terms of skin colouration: (1) adult Aurora Trout lack the yellow spots and vermiculations that typically occur on the dorsal surface of other Brook Trout; and (2) the numerous red spots surrounded by blue halos characteristically found on the sides of Brook Trout are greatly reduced in number or are absent on Aurora Trout. 

 

Distribution

The native range of the Aurora Trout consists of two small waterbodies, Whirligig Lake and Whitepine Lake, located 110 km north of Sudbury, Ontario. Reproducing populations that were established during the 1990’s in Southeast Campcot Lake and Northeast Campcot near Terrace Bay, Ontario are now extirpated. Currently, 10 other lakes in Northern Ontario contain introduced Aurora Trout populations that are maintained by stocking of hatchery-reared juvenile fish. A captive brood stock is maintained in one provincial fish culture facility near Kirkland Lake, Ontario.

 

Population Sizes and Trends

The two native populations were extirpated by lake acidification during the 1960's. Since then the stock has been maintained by artificial breeding that began in 1958 from a founding population of 6-9 individuals. The captive brood stock currently numbers 500-1000 fish. During the 1990's self-sustaining populations were reestablished in the two native lakes following water quality improvements. 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. Natural reproduction occurred in two non-native lakes (Southeast Campcot Lake, Northeast Campcot Lake) during the 1990’s, but those populations are now 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. 

 

Biology

It appears that the thermal requirements of Aurora Trout are similar to other Brook Trout. Brook Trout generally inhabit water temperatures below 20°C and when temperatures rise above that they seek cooler water by shifting their depth distribution or by inhabiting groundwater springs. At spawning time Aurora Trout, like other Brook Trout inhabiting lakes on the Canadian Shield, will seek areas of groundwater upwelling on which to build redds. A pH of at least 5.0 is required for successful reproduction and maintenance of self-sustaining populations. 

 

Limiting Factors

The native lakes are located within the zone affected by acid deposition from Sudbury metal smelters. Extirpation of the Aurora Trout during the 1960's coincided with acidification of the lakes to about pH 5.0, the threshold for Brook Trout survival. Although water quality improvements have occurred in the two native lakes since 1989 as a result of whole-lake liming and reductions in atmospheric pollution levels, the lakes are poorly buffered and they remain threatened by acidification.  The main source of acid is atmospheric deposition of pollutants, but historically deposited sulphur may also be stored in adjacent wetlands and could contribute to reacidification following drought years when oxidized sulphur is released into the lake.

The spawning sites that have been identified to date are all on groundwater springs. We speculate that the failure of stocked Aurora Trout to reproduce in most non-native lakes is due to the lack of suitable groundwater sites for spawning in the new lakes. The use of groundwater springs for both spawning and as thermal refugia leaves Aurora Trout vulnerable to land use practices (eg. logging) and climatic changes that can affect the quantity and quality of groundwater discharge to lakes. 

 

Special Significance

The Aurora Trout is a unique subspecies of the Brook Trout that is native to only two lakes in the entire world. Valued for its beauty and rarity, it was the only fish stock of hundreds that were extirpated by acidification in Ontario that is now preserved through a captive breeding program.