Sea louse (Lepeopheirus salmonis) epizootics

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 in areas adjacent to salmon farms.

WRFT has investigated the sea lice problem from 1996. Since the year 2000, early returned sea trout carrying high burdens of sea lice were recorded in the River Ewe at Poolewe and elsewehre 2001, 2003 and 2007.

WRFT fully supports the Area Management Agreement programme whereby management targets are set control sea lice on fish farms to levels at which problems for wild sea trout in surrounding waters do not occur. On-farm lice levels have improved significantly since 2000, particularly with use of the in-feed pesticide SLICE (Emamectin benzoate). However, due to the very large numbers of salmon held at fish farms, even small numbers of ovigerous lice per fish may lead to production of larval at levels one or two orders of magnitude greater than from natural sources alone. Weather and sea conditions can conspire to create problems for wild fish.

If sea trout populations such as that of Loch Maree and the important fisheries they supported (relative to other local fisheries) are to recover, a solution to the sea lice problem is prerequisite; and of highest priority.

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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)
• 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)
• WRFT Sea lice monitoring review 2007 and 2008
  Presentation given at the WRFT Sea lice Review Meeting, Gairloch 16th April 2009.  Posted: 22/09/2009 (4.63MB)