DIFFERENCES IN EARLY LIFE TRAITS, AS WELL AS THERMAL AND PH TOLERANCE OF FARM, WILD AND FIRST GENERATION (F1) FARM-WILD HYBRID ATLANTIC SALMON IN THE SOUTH COAST OF NEWFOUNDLAND (NL), CANADA.  

The gene flow from farm escapees into native population can be low in relation to number of escapees on the spawning grounds; this is likely due to the reduced spawning success of escapees, and lower survival of hybrid offspring when compared with native conspecifics. In NL, all farm Atlantic salmon originate from New Brunswick and are genetically distinct from local stocks.  The NL environment is characterized by acidic river waters in the south coast and cold spring seawater temperatures that can affect fish osmoregulatory mechanisms. In the first part of this study, we explore fertilization rates and survival to eyed-stage of pure farm, wild and F1 hybrid eggs in river conditions by setting up reproduction trials followed by the documentation of early life trait differences in tank conditions. The second part consists of two assessments: the influence of low pH (in freshwater) on parr survival, growth and smoltification of the three abovementioned fish groups, and the effect of low temperatures (in seawater) on mortality. Our findings show that wild females' progeny (pure wild and hybrids with wild mothers) hatched 7 to 11 days earlier than pure farm crosses and hybrids with farm mothers. In addition, pure wild progeny had higher total lengths at hatch than pure farm crosses and hybrids confirming the maternal influence on early stages. Differences in length were no longer significant at 70 days post hatch. Higher mortality rates of the most likely hybrids (farm female x wild male hybrids) at egg and fry stages and their delayed hatch suggest that they might be less likely to survive the early larval stages than wild stocks (Table 1). Our results show also that a 90-day exposure to low pH water does not influence survival, growth or seawater readiness of F1 hybrids at the parr stage. In addition, F1 hybrids are as likely to survive seawater migration in cold temperatures as their wild counterparts.