Sea lice monitoring

The sea louse, Lepeophtheirus salmonis is a natural parasite of salmon and sea trout. The natural host - parasite ecology of sea trout with the sea louse Lepeopheirus salmonis is finely balanced. Even prior to the onset of salmon farming, sea trout with 10 or more attached lice were commonly seen around the coasts. However, from the late 1980s much higher levels of lice infestation were found on sea trout, especially closest to fish farming areas. Sea lice epizootics remain one of the biggest problems for sea trout fisheries in Wester Ross.

WRFT has recorded sea lice abundance on sea-trout during the month of June in estuaries at Dundonnell and Poolewe since 1997. Data has also been collected describing sea lice abundance on sea trout at other sites and at other times. Heavily infected sea trout tend to return prematurely from the sea to freshwater. During years when there are sea lice epizootics, many 'early returned' sea trout ranging in size from post-smolts of less than 25cm to fish which have spent one or more summers at sea previously are recorded. Older sea trout of more than 45cm have rarely been taken in recent years.

Similar monitoring is carried out by scientists working for Fisheries Research Services in Loch Torridon. In 2008, the sea lice monitoring programme will be extended to include a series of sweep nettings in sea lochs throughout the WRFT area. This work is to be funded by the Scottish Government, via the Tripartite Working Group.

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• Dundonnell fyke net sea trout sea lice results 2008
  Spreadsheed with details of lice counts on sea trout taken in the Dundonnell fyke net in June and July 2008, operated by Eilean Darach Estate and Dundonnell Estate. many thanks to respective estates for permissions to post these results.  Posted: 10/09/2008 (74KB)
• Estuarine trout, Kerry Bay 7 June 2010
  This trout, the largest taken in the sea by the WRFT sea lice monitoring team, was taken in the sweep net; and the file shows photographs of scales from which the age has been assessed. .  Posted: 07/06/2010 (508KB)
• WRFT sea lice monitoring Report 2007 - 2008
  Following a review of sea lice biology and ecology and past studies from a local context, this report presents the results of sea lice monitoring of wild sea trout in the WRFT area in 2007 and 2008 and considers associations with salmon farming.  Posted: 19/11/2009 (2.29MB)