Ecological interactions between juvenile diploid and triploid Atlantic salmon (Salmo salar L.)

The possible use of sterile (triploid) salmon in the aquaculture industry relies on their reduced negative effects, both genetically and behaviourally, on dwindling wild populations in the event of escapes. Juvenile aquaculture salmon are found in rivers via escapes from hatcheries or as a result of successful spawning from mature escapees. The use of triploid salmon would eliminate the possibility of the latter mechanism but the potential for behavioural interactions have yet to be investigated. The aim of this project was to investigate ecological interactions between juvenile diploid and triploid Atlantic salmon (Salmo salar) using a semi-natural rearing system. Individual fish were identified using Visible Implant Elastomers (VIEs) in varying colours and tag locations. Multiple tags could be applied to a large size range of diploid and triploid salmon without affecting growth or survival. Specific growth rate (SGR) and emigration were evaluated for diploids and triploids reared separately and in combinations. Regardless of combination, ploidy did not significantly affect mean SGR. Generally, the fish that emigrated from the competition arena had lower SGR than the residents. Ploidy and rearing combinations also did not affect emigration patterns (i.e., average day of emigration, percent fish emigrated and cumulative emigration). It appears that triploid salmon are similarly competitive as diploid salmon in a semi-natural environment when considering SGR and emigration as measures of success. Increasing numbers of the other ploidy did not affect this outcome. Although triploid salmon may provide a viable solution for negating the genetic impact of aquaculture escapees, it appears that they are just as likely as diploid escapees to cause displacement of wild salmon.