Early marine survival and movements of escaped Atlantic salmon Salmo salar L. juveniles from a land-based smolt farm during autumn

摘要

The aim of this study was to examine early marine survival and movements of simulated escaped Atlantic salmon Salmo salar L. pre-smolt and smolt from a commercial smolt farm during autumn. One-third of the pre-smolt most likely died in the immediate vicinity of the release location, whereas the corresponding mortality for smolts was lower (8.5%) during the 5-week study period. The surviving pre-smolt left the farm area after 2-3days, predominantly along the shore. In contrast, most of the surviving smolts left the farm area during the first day and 54% seemed to move away from the shore and adopt a more pelagic movement pattern than pre-smolt. The number of surviving fish recorded in the fjord decreased throughout the study period, possibly due to a combination of fish migrating out of the fjord or undetected mortality. Compared with existing knowledge on migration of released farmed smolts during spring, our results indicate less directional and slower movement rates during autumn. Only two of the tagged fish were detected upstream in the rivers following release. A rapid dispersion of escapees indicates that the potential for recapturing escapees is limited unless recapture efforts are initiated immediately after escape. Hence, there is a need for development of technology that detects and prevents escapees to enter the sea.