Testing the Feasibility and Effectiveness of Genetic Restoration of Aurora Trout Salvelinus fontinalis timagamiensis

Genetic restoration has been used with varying degrees of success across a range of taxa by translocating unrelated individuals.  This approach entails some risk; by contrast, using experimental breeding crosses in controlled environments can test the feasibility of ‘genetic restoration’ for enhancing genetic variation and fitness in target populations without risking outbreeding depression and irreversible genetic loss in populations of conservation concern.

The aurora trout (Salvelinus fontinalis timagamiensis), a subspecies of brook trout, was formerly native to two lakes in northeastern Ontario before becoming extirpated from the wild 50 years ago as a result of acid rain.  At the time, nine individuals were captured and used to found a captive hatchery population, but with so few founder individuals and several generations of captive breeding, inbreeding depression has been identified as a significant risk to their long term survival. 

Introgression with wild-type brook trout has shown increased fitness in F₁ hybrids, as well as significant maternal effects on hybrid fitness.  We investigated the potential for genetic restoration in the aurora trout as well as the maintenance of their unique phenotype by monitoring the survival and comparative life history of F₂ hybrid and several backcross types in captivity and the wild.  Equal numbers of aurora trout and two backcross types were stocked into two inland lakes at 2kg per hectare.  Each treatment type was uniquely marked to facilitate population abundance estimates at year one and two by mark-recapture and short duration gill-net index netting, recording hybrid type, relative abundance, length, weight, and phenotype of all captured fish.  Concurrently, hatchery trials are assessing the comparative life history of second-generation crosses (parent types, F₁ and F₂ bidirectional hybrids, and backcrosses) for survival, growth, maturity, and fecundity. 

Preliminary results show clear fitness differences among pure and backcross aurora trout, with enhanced survival and performance of introgressed fish.  Based on treatment performance under benign (hatchery) conditions, it is predicted that backcross hybrids will display significantly higher survival and fitness in the wild than genetically pure aurora trout, and may provide an opportunity to restore the genetic and ecological fitness of aurora trout without compromising their phenotypic and evolutionary distinctiveness.