Search

We report genetic differences for resistance to the pathogen Listonella anguillarum within and among one cultured and two wild Canadian populations of Atlantic salmon, Salmo salar, using a common-garden experimental protocol. Following exposure to the causative agent for vibriosis, parr originating from the endangered Stewiacke River population experienced significantly higher mortality than cultured parr, four generations removed from the Saint John River population, and wild parr from Tusket River. Pathogen resistance differed between sexes; males consistently experienced higher survival than females. There was no evidence that maturity influenced pathogen resistance in male parr. The population and sex differences in pathogen resistance documented here have implications for risk assessments of the demographic consequences of interbreeding between wild and farmed Atlantic salmon.

Annual and seasonal trends in sightings of coastal cetaceans near Halifax, Nova Scotia, were studied using observations from whale watching and dedicated research vessels from late spring to early fall of 1996 to 2005. Four species of cetaceans routinely used the area during the summer: White-beaked and Atlantic White-sided dolphins (Lagenorhynchus albirostris and L. acutus), Harbour Porpoises (Phocoena phocoena), and Minke Whales (Balaenoptera acutorostrata). The dolphin species were temporally separated, with White-beaked Dolphins being common earlier in the summer than White-sided Dolphins. White-sided Dolphins were unusually abundant in 1997, and were found in larger groups (mean = 46.5 ± 46.19 sd) than Whitebeaked Dolphins (mean = 9.1 ± 5.19 SD). The area also appears to be an important habitat for dolphin calves and juveniles of both species. Fin Whales (B. physalus) were commonly observed in relatively large groups in 1997, but were uncommon or absent in other years. Humpback Whales (Megaptera novaeangliae), Blue Whales (B. musculus) and North Atlantic Right Whales (Eubalaena glacialis) were uncommon in the area, although Humpback Whales were sighted frequently in 1997. Increased numbers of White-sided Dolphins, Fin and Humpback whales in 1997 may be explained by increased prey abundance and decreased sea-surface temperatures.

Introgression between wild and farmed Atlantic salmon Salmo salar has been hypothesized to influence the persistence of wild populations, particularly those at heightened risk of extinction. Based on pure and hybrid crosses involving one farmed and two wild populations (Tusket River and Stewiacke River, an endangered population) in a common-garden environment, we examined the consequences of introgression to survival, growth, and disease resistance in the first year of life. Introgression with farmed salmon had either no effect (Stewiacke) or a negative effect (Tusket) on survival. Importantly, the among-family variance in survival (a negative correlate of population persistence) was higher for the hybrids than it was among the pure crosses. There was also evidence of genetic differences in growth rate and disease susceptibility. Introgression with their farmed counterparts is unlikely to have a positive effect on the fitness of wild Atlantic salmon. The degree to which genetic interactions between farmed and wild salmon threaten the latter's persistence almost certainly depends on the degree to which individuals are adapted to their local environment, on the genetic differentiation between farmed and wild individuals, and on the relative proportions of farmed and wild salmon during spawning.