Experimental comparison of changes in relative survival and fitness-related traits of wild, farm, and hybrid Atlantic salmon Salmo salar in nature

Abstract

Farming of Atlantic salmon Salmo salar has resulted in highly domesticated individuals, with notable genetic and phenotypic differences from their wild counterparts. Understanding how interbreeding with aquaculture escapees affects wild, often at-risk populations is increasingly essential to conservation efforts. Here, we used an experimental release of wild, farm, and reciprocal F1 hybrid fry at 3 sites in the Garnish River in Newfoundland, Canada, to evaluate family and cross-specific patterns of recapture/survival, size, sex ratio, and precocial male maturation over a 28 mo period. Trends in cross type recapture changed over the study period, with the highest recapture at 3 mo in parr with wild mothers and between 15 and 28 mo in aquaculture offspring. Size trends among crosses and sites remained consistent over the study duration, with pure farm and wild-mother hybrids being consistently larger than wild individuals and 1 site displaying elevated sizes in all crosses. Rates of parr maturation differed by sex and cross type, and family-based analysis indicated family representation and size also remained consistent through time. These results indicate there is a difference in vital rates such as survival and precocial maturation between farm and wild Atlantic salmon during the freshwater early life history period, and this difference can change significantly over time. As such, an improved understanding of genetic and ecological interactions which takes this ontogenetic variation into account is likely essential to fully understand how hybridization and introgression with farm escapees are affecting wild populations.