Experimental and genetic evaluation of the impacts of hybridization and introgression of farmed Atlantic salmon (Salmo salar) into wild populations

San Roman, Coral (2024) Experimental and genetic evaluation of the impacts of hybridization and introgression of farmed Atlantic salmon (Salmo salar) into wild populations. Masters thesis, Memorial University of Newfoundland.

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Abstract

Marine aquaculture of Atlantic salmon (Salmo salar) has been ongoing for several generations, during which farmed fish have experienced different selection pressures relative to their wild counterparts. The number of domesticated individuals exceeds wild individuals, and escape events occur regularly, yet current understanding of the long-term effects of interbreeding on population productivity and life history traits is limited. Therefore, understanding the impacts of farm introgression on relative survival and performance of wild Atlantic salmon is critical to manage the impacts of aquaculture escapees on threatened wild populations. In my first data chapter, I compared cross specific patterns of survival, size, sex ratio, and precocial male maturation over a 28-month period from an experimental release of wild, farm, and reciprocal F1 hybrid fry in southern Newfoundland. Trends in cross type survival changed over the study period, while size trends remained consistent. Parr with wild mothers had the highest recapture at 3-months, while aquaculture offspring had the highest rates of recapture at 15-28 months. Throughout the duration of the study, pure farm and wild-mother hybrids consistently being larger than wild individuals, and rates of parr maturation differed by sex and cross type. In my second data chapter, I evaluated the presence of hybridization and subsequent introgression of escaped farmed salmon into 18 southern Newfoundland rivers and estimated the number of successfully breeding escapees over an 8-year period encompassing three reported escape events. Results from these analyses demonstrated an increasing proportion of backcross-wild hybrid individuals with a consistent occurrence of F1s every year, and most rivers exhibited evidence of farm admixture. Additionally, at least one successfully breeding farm parent was detected annually. Overall, the research presented here provides insight into the consequences of escape events and direct genetic interactions and informs conservation actions for at risk populations.

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