Visibility of visual implant elastomer tags in Atlantic salmon reared for two years in marine net-pens

We evaluated detectability of visual implant elastomer (VIE) tags in individual Atlantic salmon Salmo salar reared from smolts to adults in commercial marine net-pens. A total of 9,000 individual smolts were marked (adipose eye, lower jaw, or both) with colored VIE tags. During the period from March 1998 to December 2000 (2-28 months after tagging) a total of 3,220 fish were visually inspected for VIE tags. Tag detection rates remained high (>90%) for the first 17 months after tagging but then declined sharply, particularly for VIEs in the jaw. Use of a UV light significantly increased detection of both eye and jaw VIE tags. We conclude that VIE tags are optimal for use in Atlantic salmon when recovery of fish occurs within 17 months of tagging.