Aurora trout COSEWIC assessment and status report: chapter 5

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Species Information

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. This form likely evolved from Brook Trout that were isolated after the continental glaciers receded from that area about 10 000 years ago. The Aurora Trout was originally described as a distinct species (=Salvelinus timagamiensis) (Henn and Rickenbach 1925), but Martin (1939) considered it a subspecies of the Brook Trout and Vladykov (1954) referred to it as a Brook Trout colour variant. Subsequently, arguments were made for subspecies designation (Salvelinus fontinalis timagamiensis) based upon studies that included the original populations in Whitepine and Whirligig Lakes (Sale 1967; Qadri 1968; Behnke 1980). The significant differences that were identified between Aurora Trout and other Brook Trout included: (1) colouration; (2) skeletal structure (eg. numbers of trunk vertebrae, single neural spines, epineurals, strongly bifid ribs); and (3) spawning behaviour, as implied by reproductive isolation with little apparent hybridization between the sympatric populations of Aurora Trout and normal type Brook Trout in Whitepine Lake. In lakes other than Whitepine Lake Aurora Trout do hybridize with other Brook Trout (Sale 1967). The recent genetic analyses done on hatchery-reared Aurora Trout (McGlade 1981; Grewe et al. 1990) have not supported subspecies designation, but the significance of the results is uncertain because the extant gene pool originated from a small number of founders and thus may have less variation than the original populations. Allozyme data indicate that the Aurora Trout is the most genetically uniform of the 99 Brook Trout stocks in Ontario that have been evaluated (P. Ihssen, pers. comm., Ontario Ministry of Natural Resources, Box 7000, 3rd Floor N, 300 Water St., Peterborough, Ontario K9N 8M5). The low genetic diversity may be natural and reflect narrow adaptation to the home environment by the original wild stock, or, alternatively it may have arisen more recently when captive breeding began from a small founding population. We think the case for subspecies status made by Sale (1967) and Qadri (1968) and supported by Behnke (1980) has merit, in particular because Aurora Trout were observed in Whitepine Lake between the 1920's and 1950's to exist as a distinct form living sympatrically with normal type Brook Trout.