First results from a new method of tagging salmon - the coded wire tag

Abstract

This leaflet describes the use of a new and highly sophisticated method of tagging salmon. The tag is a microscopic piece of steel carrying a binary-coded number. It is injected into the nose of the young fish and can be recovered at any time subsequently by passing the fish through a magnetic detector. More than 127,000 juvenile salmon were tagged in 1979 and the first of these were recaptured as grilse in the summer of 1981. Research work initiated by Eileen Twomey in 1975 at the Fisheries Research Centre showed that hatchery-reared smolts were making a significant contribution to the national salmon catch. Hatchery-reared fish are recognised by the absence of the adipose fin which is clipped off before the fish are released. The adipose fin is generally thought to be rudimentary and its removal does not seem to affect the fish in any way. The results obtained showed that the proportion of hatchery-reared fish in the commercial catch varied from 2% in the Northwest to 13% on the Clare and Galway coasts. This work gave information on the contribution of hatcheries to the national salmon harvest. The Electricity Supply Board (ESB) have proposals to increase significantly the production of reared smolts for release. It is clearly essential to have information on the survival of hatchery salmon, on the efficiency of various rearing stations and on aspects of husbandry such as the best time for releasing the young fish. This information cannot be obtained by the fin-clipping technique alone but the coded wire tag can provide the answers to many of the vital questions.