Abstract
Escaped farmed Atlantic salmon represent a well-documented and ongoing threat to wild conspecific populations. In Norway, the world-leading producer of farmed salmon, annual monitoring of straying and genetic introgression by farmed escapees in wild salmon rivers has been carried out since the late 1980s. In this study, we applied molecular and statistical methods routinely used in the Norwegian monitoring programme to investigate the magnitude of escaped farmed salmon and genetic introgression in salmon rivers on the west coast of Sweden, where suspected escapees have been observed. Our results confirm that escaped farmed salmon stray, successfully spawn, and produce offspring at levels similar to those observed in neighbouring Norway. These findings raise concerns over population productivity and long-term viability and highlight the need for more permanent monitoring of the presence and consequences of escaped farmed salmon in Swedish salmon rivers. Our results further illustrate that farmed gene flow may constitute a transboundary problem with potential international implications.
Highlights
During the last half-century, aquaculture production of Atlantic salmon Salmo salar Linnaeus, 1758 for the international food market has increased dramatically (Bostock et al 2010)
Using well-established methods routinely applied in the ongoing Norwegian monitoring programme, we provide the first scientific evidence for straying of adult salmon of farmed origin into Swedish rivers
Analyses of naturally spawned juveniles further revealed that escaped farmed salmon have successfully reproduced in several watercourses
Summary
During the last half-century, aquaculture production of Atlantic salmon Salmo salar Linnaeus, 1758 for the international food market has increased dramatically (Bostock et al 2010). Our main rivers at an even closer distance where straying and aims were (1) to identify potential escapees among genetic introgression by escaped farmed salmon adult salmon previously analysed with microsatelhave been detected, there is so far no conclusive sci- lites, and (2) to provide a first assessment of levels of entific evidence for similar problems in south-west- farmed introgression in Swedish wild salmon popuern Sweden (Kattegat/Skagerrak area). In this part of lations based on juvenile samples. Sweden has no sea-based salmon farming from which adults may
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