Behavioral and Genetic Interactions Between Escaped Farm Salmon and Wild Atlantic Salmon
The production of Atlantic salmon (Salmo salar) dwarfs the wild salmon fishery by two orders of magnitude. Throughout the North Atlantic region, large numbers of aquacultured (farm) fish escape and invade rivers that contain native salmon. This causes considerable concern, because interactions between escaped farm fish and native fish can cause a decline in the fitness and productivity of the native stock. Norwegian farm salmon originate from salmon collections taken from wild populations in the early 1970s. They have been under artificial selection for growth rate, age at maturity, disease resistance, and flesh quality. Farm strains have changed genetically relative to the original populations from which they were taken and they have lost allelic variation compared to wild populations. Escaped farm salmon can spawn successfully in the wild, but their breeding performance can be inferior to that of wild salmon. Farm offspring outgrow those of wild origin, both under artificial and natural conditions. Farm juveniles also differ in aggressive behavior and dominance relative to wild juveniles, and they appear to suffer higher mortality during early life stages, possibly due to their lower response to predation risk. Farm-X-wild offspring are behaviorally intermediate between farm and wild juveniles, and show superior growth compared to wild juveniles. In a whole-river experiment, we showed that the lifetime reproductive success of farm salmon was 16% that of the native salmon. Differential selection against farm-salmon genotypes occurred during breeding and early survival but was similar to that of wild salmon thereafter, despite significant ecological differences between the two groups. The overall productivity of the population, however, appeared depressed. Our findings suggest that gene flow from escaped farm fish to native fish will lead to genetic and behavioral changes in wild populations in the direction of domesticated salmon. Moreover, wild populations may suffer depressed productivity caused by ecological interactions with escaped farm salmon and their offspring. These findings call into question the long-term viability of many salmon populations.
KeywordsMigration Depression Europe Arena Aqua
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