While catch statistics are a very useful tool in determining the number of Irish salmon caught, it is also critical that we know how many are left to breed for future generations. To help us do this the salmon tagging programme was set up in 1979 in a bid to determine exploitation rates of salmon stocks in high seas fisheries, and in Irish commercial and recreational fisheries. In addition, specific experiments were undertaken to improve the performance of hatchery reared juveniles released and to improve our knowledge of overall performance of Irish stocks.
Tag returns provide continuous information on migration patterns, stock composition, straying, return timing, growth rates, feeding patterns, predation, fish farm escapees and rates of escapement to spawn.
With an impressive track record of over 8 million tagged smolts going to sea over a 35 year period - a virtual treasure trove now exists for scientists investigating the impacts of global warming, especially throughout the critical North Atlantic area.
Salmon tagging involves the placement of a coded microscopic tag into the nose of wild and hatchery reared fish before their migration to sea. Tagging large numbers requires co-operation with the Inland Fisheries Ireland, Electricity Supply Board (ESB) and several private fishery owners throughout Ireland.
Up to 250,000 salmon smolts are tagged each year as they leave rivers such as Burrishoole, Corrib, Erne, Lee and Shannon on their migration to sea.
To obtain as complete a picture as possible, fish are examined for tags wherever they are caught, whether by nets, rods, traps or in broodstock recovery programmes. Surveillance is mounted by the Marine Institute both within and outside the salmon fishing season. In the past, co-operation with fishermen, fish processors and Fishery Co-Ops was such that between 25 and 50% of the declared net catch was examined annually.
In 2007, the closure of the drift net fishery heralded a new area for salmon stock assessment. The tag recovery programme moved inshore with the fisheries and rivers remaining open were targeted for sampling and tag recovery.
The difficulty of finding quick answers is highlighted in the appearance of Irish stocks as far away as West Greenland. This was first established when tagged salmon were seen among catches there in 1963. Since the 1960's European salmon entering the fishery have fallen in size and are now similar to that of their Northern American cohorts.
In recent years experimental post-smolt trawls in the Norwegian sea and Western Scotland have provided invaluable evidence for a northerly migration route for Irish salmon stocks in the early months of their long migration. Slowly, over the last twenty years or so a picture of the mysterious Atlantic salmon oceanic journey is beginning to emerge and illuminate our understanding of the factors which may be responsible for recent and continuing high mortality rates at sea.