Survival of farmed, wild and first generation hybrid Atlantic salmon (Salmo salar Linnaeus, 1758) to low temperatures following seawater transfer

In Newfoundland and Labrador, all farmed Atlantic salmon originate from the Saint John River strain (New Brunswick), raising the question of impacts of escapees on wild, genetically distinct stocks. While adverse genetic changes due to hybridization between farmed and wild salmon might not be manifested until the second generation (F2), the existence of F2 or later generations depends ultimately on the survival of F1 hybrids. After smoltification, cold spring seawater temperatures (1.5-5 degrees C) such as those observed on the south coast of Newfoundland can be problematic to salmon as the combination of abrupt seawater exposure and cold temperature is known to overwhelm osmoregulatory mechanisms. No significant differences in total mortality were observed among wild, farmed and F1 hybrids after transfer to seawater and exposure to very cold temperatures. Our findings suggest that farmed salmon and F1 hybrids resulting from crossing wild salmon and St John River farm salmon are as likely to survive seawater migration in cold temperatures as their wild counterparts.