Novel restoration strategy using marine rearing increased fitness and genetic diversity in an endangered Atlantic salmon (Salmo salar) population

Atlantic salmon ( Salmo salar ) have declined precipitously throughout most of their North American range, and many restoration strategies have been implemented to aid recovery. One such restoration strategy, implemented by the Fundy Salmon Recovery project, involves collecting endangered inner Bay of Fundy Atlantic salmon smolts from their natal rivers, rearing to maturity in modified marine sea cages, and releasing back to their natal rivers. An alternate strategy involves rearing parr collected from an isolated brook to sexual maturity at a freshwater hatchery. Releases include two approaches: release by hand (carrying fish to the water); or by carefully lowering fish into pools using a helicopter. We aimed to evaluate the efficacy of these rearing and release strategies on offspring production following release in two Fundy National Park rivers. Single nucleotide polymorphisms (SNPs) were used to match parents with their offspring using Colony, a parentage analysis software. There was no significant effect of release strategy on offspring production. Rearing strategy had a significant effect on offspring production, with marine-reared adults producing 4.1 times more offspring per individual than freshwater-reared adults. Also, the effective number of breeders was higher with wild spawning smolt-to-adult-reared Atlantic salmon. This study highlights the utility of genetic analysis to evaluate rearing and release strategies in aquaculture-aided enhancement programs.