Salmon Tagging in the West of Ireland 1986 to 1988

Abstract

The analysis of more than twenty-six thousand micro-tag recoveries has led to important discoveries for the management of Irish salmon stocks. This Leaflet gives details of the tagging over half a million young salmon and of the results of recovering 4,000 tags from 1986 to 1988. The most important conclusions are: Careful control of place and time of release of hatchery-reared smolts has a dramatic effect on their survival. In the Corrib system, transportation of smolts from Cong to Galway resulted in a substantial improvement in yield, with a tenfold increase on one occasion. This means that up to ten times as many salmon can be produced at no increase in the cost of rearing them. The returning adult salmon produced from smolts which were released at Galway tended to stay for a long time below the Galway weir and therefore made a major contribution to the rod fishery. Marine survival fluctuated yearly for hatchery and wild smolts released. For hatchery smolts those released later survived best. In contrast wild smolts which migrated in May had a lower survival than those which left in April. Marked differences in homing accuracy, timing and speed of migration were noted between wild and hatchery smolts within the Corrib system. Drift net fisheries depend mainly on the salmon which originate from rivers nearby. There is a distinct division between the catches north and south of Galway Bay: those to the south come mostly from the rivers Shannon and Corrib, those to the north from Connemara rivers. The drift net fishery continues to rely heavily on a self sustaining population of wild salmon despite improved hatchery performance and increasing catch of cage farm escapees. Hatchery smolts transferred to different rivers learned to recognise the new river within a remarkably short time. Two weeks were sufficient to achieve a degree of homing success approaching that of fish returning to their own rivers. This discovery is of major significance in the development of salmon ranching.