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Sea louse (Lepeopheirus salmonis) epizootics

Sea lice

Sea lice

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.

Over 300 sea lice were counted on this sea trout

Over 300 sea lice were counted on this sea trout caught in the River Ewe in May 2007

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    This presentation by Peter Cunningham introduces the main wild salmon rivers that flow into the Wester Ross MPA and describes some of the issues, including infestation by sea lice from poorly regulated open cage salmon farms, which threaten wild salmon populations and sea trout within the Wester Ross area. Can the wild salmon populations around the Wester Ross MPA be given additional protection?.  Posted: 27/10/2022 (11.01MB)
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  • Wester Ross: a stronghold for wild trout diversity? Presentation by Peter Cunningham 30th April 2019
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  • Gairloch sea trout sample 19th April 2019
    This file provides details of a sample of 30 sea trout taken using a sweep net in the Flowerdale estuary, Loch Gairloch on 19th April 2019. These fish carried high numbers of sea lice. .  Posted: 22/04/2019 (536KB)
  • Skye and Wester Ross Fisheries Trust Review February 2018
    This review summarises the work of the Skye and Wester Ross Fisheries Trust during the period June 2016 to December 2018.  Posted: 06/02/2018 (7.46MB)
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  • WRFT Review May 2016
    This review covers the period February 2015 to April 2016, and presents summaries describing the status of wild fish populations, the results of sea trout and sea lice monitoring work including sea trout around the Loch Torridon area, a summary of the activities of the Skye Fisheries Trust, work to monitor and control invasive species, a section on education and student project and much else.  Posted: 19/05/2016 (6.18MB)
  • Loch Torridon Sea trout report 2015
    This report presents some of the results of investigations to gather information about sea trout around the Loch Torridon area in 2015 following reports of exceptionally high concentrations of parasitic sea lice (Lepeophtheirus salmonis) on salmon farms within the area during the first six months of 2015 . Sea trout were sampled by Wester Ross Fisheries Trust during the period May-July 2015 using sweep netting, rod and line and electro-fishing. In October and early November 2015 a fyke net trap was operated in a tributary of the River Torridon to learn more about the spawning population of trout within that river system.  Posted: 05/01/2016 (7.75MB)
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  • Problems for Sea trout in Wester Ross
    This presentation has been tidied up from one given at the sea trout and sea lice management workshop at Aultbea Village hall on 20th February 2014. Data for sea lice and other factors affecting sea trout in Wester Ross are summarised. The presentation concludes with an outline for a Scottish Sea Trout Project aimed at improving our understanding of how different factors affect sea trout in different parts of Scotland.  Posted: 21/02/2014 (6.57MB)
  • WRFT Sea trout Monitoring review 2012
    This report presents the results of sea trout and sea lice monitoring in 2012 within the WRFT area, and considers the occurrence of larger sea trout in Wester Ross and other parts of the West of Scotland.  Posted: 12/04/2013 (6.05MB)
  • WRFT Sea trout monitoring report 2009 - spring 2011
    Sea trout sampling in Wester Ross from 2009 to spring 2011. Includes results of sweep net sampling and links to scale reading catalogue.  Posted: 11/04/2011 (1.95MB)
  • Wester Ross Sea Trout Scale Catalogue April 2011
    The document provides links to photographs of sea trout and their scales from the sea and river estuaries of Wester Ross. The catalogue will be updated in response to comments received.  Posted: 05/04/2011 (989KB)
  • Sea trout 315mm River Ewe 20 June 2007
    Sea trout 315mm River Ewe 20 June 2007, early returned lice-damaged fish.  Posted: 14/03/2011 (200KB)
  • 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)
  • 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)