Satellite project to track eel migration

Irish marine scientists have revealed details of a research project to investigate the dramatic decline in eel stocks on the country's rivers and lakes.

Eels are the only freshwater fish that spawn at sea and are believed to migrate from Ireland to the Sargasso Sea. However their migration patterns and the exact location of the spawning grounds remain a mystery.

Scientists from the Central Fisheries Board and the Marine Institute have launched an experiment with colleagues in Denmark and Norway using satellite technology to monitor the eels' 5,000-mile journey across the Atlantic Ocean.

Dr Patrick Gargan of the Central Fisheries Board told The Irish Times that "the findings could provide definitive proof of the location of the spawning grounds and help to explain what is causing the collapse of eel numbers migrating back to Ireland and Europe over the past decade".

Last month 22 Irish eels were fitted with electronic tags, costing €4,000 apiece, and released into Galway Bay.

The tags will record depth, temperature and light on the migration route across the Atlantic and have been designed to "pop-off" at pre-scheduled times up to April 2007.

The Argos satellite will pick up signals from the tags when they float to the water's surface. Dr Gargan said the final tags were expected to surface "somewhere in the Sargasso Sea next April, thus revealing the precise location of the spawning grounds".

The satellite will transmit the GPS positions of the tags to a Danish research vessel which is scheduled to be in the area. A trawl of the area will be undertaken in an attempt to catch the spawning eels.

The Galathea 3 ship, with 60 scientists on board, is "the most extensive Danish research expedition at sea for more than 50 years" and has the support of the Danish government.

Scientists are also hoping that the experiment will shed more light on why eels are increasingly infected with a swim-bladder parasite, the anguillicola crassus, which may be hampering their ability to cross the Atlantic and contributing to the decline in stocks.

"The venture is historic because no adult eel has ever been found in the Sargasso Sea," Dr Gargan said.

The Sargasso Sea, covering an area the size of Australia, is located between Florida and the Azores and is notorious among sailors as the location of the Bermuda Triangle. It has a high salt content, an abundance of a seaweed called sargassum and lacks the nutrients most fish need.

However, it has long been believed that freshwater eels from Europe and America migrate there to spawn.

Each female eel can hatch up to 20 million eggs and the elvers (young eels) are believed to return to European and American rivers after about three years. Dr Gargan said that the first results of the research should be available by early next summer.

Traditionally, the main locations for eel fisheries in Ireland are Lough Neagh, the Shannon and Corrib, Lough Mask and the Barrow, Nore and Suir rivers.

Lar Butler, who once operated an eel fishery and processing facility at Graiguenamanagh, Co Kilkenny, said: "Stocks have vanished on rivers in the south over the past 10 to 15 years.

"Once there were 12 eel fisheries on the Barrow, Nore and Suir and today they have all closed".