Horizontal movements of simulated escaped farmed Atlantic salmon (Salmo salar) in a western Norwegian fjord

Skilbrei, O. T., Holst, J. C., Asplin, L., and Mortensen, S. 2010. Horizontal movements of simulated escaped farmed Atlantic salmon (Salmo salar) in a western Norwegian fjord. – ICES Journal of Marine Science, 67: 1206–1215. The dispersal of simulated escaped farmed Atlantic salmon (Salmo salar) in Hardangerfjord in western Norway was studied by telemetry. Tagged fish were released from fish farms on five different dates in the course of 1 year. Irrespective of the time of year, the fish dispersed rapidly, with a mean displacement from the release site of 5–7 km after 1 d, and 9–12 km after 2 d. Individual rates of movement varied, but were much higher than the rate of displacement from the release site, as fish moved around in the fjord basin in all directions. As a result, the fish were spread over an area of more than 500 km2 after 1 week. The number of released fish recorded in the fjord gradually declined after each release from ∼40% remaining in the fjord after 3 weeks to few or none after 7 weeks. In all, 38% moved out of the fjord, and 36 and 2% were reported as captured inside and outside the fjord, respectively. Their rapid dispersal suggests that concentrating efforts to recapture escaped salmon in the proximity of an escape site will probably not be successful, at least from locations of this type. In fact, the recaptures demonstrate that it is both necessary and possible to expand the fishing effort to cover a large area and to sustain it for several weeks to attain high rates of recapture. The wide dispersal of escaped fish potentially acting as vectors within the fjord basin also has implications for the spread of disease and parasites.