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NATURE Sea lice, a salmon’s scourge

Outdoor Living
The sea louse lives off the skin, blood and mucus of a host salmon
The sea louse lives off the skin, blood and mucus of a host salmon

New season, same problems

Marine Life
John Paul Tiernan

As salmon begin arriving back to our county’s rivers from their epic journeys through the North Atlantic, they do so oblivious to the interest, concern, intense research and sometimes conflict their existence generates among humans on the west coast of Ireland. The IFI, NWRFB, NIG, DAFF and SWI are all acronyms of organisations and boards that seek to serve, maintain and somehow benefit from this almighty fish.
A new draft of regulations by the Minister of State, in liaison with the Inland Fisheries Ireland and The North West Regional Fisheries Board, await the opening of rivers, including Carrowmore lake (already open), River Moy, Owenduff  and Owenmore (February 1), Newport River (March 20) and Glenamoy (May 1) – catch-and-release last year but now open for harvest, and Burrishoole (June 1). Info on the regulations for 2011 including how many fish can be bagged and what to do with tags can be found on
Meanwhile their caged counterparts, who never leave our bays, attract attention at all times of the year, most of it negative. It is hard to make a story about lice sound good, but end-of-year reports from NIG (National Implementation Group) in the DAFF (Department of Agriculture, Fisheries and Food) for 2010 last year are that the levels of egg-bearing lice in salmon farms around the country are down. Too good to be true? Probably. In fact, 53 per cent of inspections last year exceeded acceptable levels. Production was down, which brought down the overall total, but levels of sea lice were still too high, and still doing severe damage to wild stocks according to SWI (Salmon Watch Ireland).
It’s not often one can describe a small sea creature as wholly unpleasant and not much good for anything, but the salmon louse might be such an example. Between 0.5 and 5 mm, they live off the skin, blood and mucus of the host salmon. In a natural environment it is common for a few sea lice to attach themselves to a salmon, which doesn’t impact the fish terribly. However, in a restricted environment at high densities, their populations swell and begin to affect local wild stocks of salmon and trout.
They are controlled on farms by measures, including keeping pens apart from one another and the introduction of wrasse, which eat the lice, but mostly through the use of chemicals, which are as strong as their names are unpronounceable (Cypermethrin, Enamectin-Benzoate & Teflubenzourn).
After 30 years of salmon farming in Ireland, however, it seems no one and no thing can solve the divisive problem of the unassailable sea louse.

John Paul Tiernan, Louisburgh, runs, a website dedicated to the creation of knowledge of our marine ecosystems. He is currently studying for an MSc in Marine Science.