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Sea lice monitoring

Sweep netting for sea trout at Kildonan Bay, Little Loch Broom

Sweep netting for sea trout at Kildonan Bay, Little Loch Broom

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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    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)
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    Summary report from sweep netting of sea trout in Flowerdale estuary, Loch Gairloch on 27th April 2017. 32 sea trout were caught, with an estimated average lice burden of 98 lice per fish. .  Posted: 01/05/2017 (1.85MB)
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    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)
  • Costello, Scotland 2014: The problem for sea lice on salmonids: wild and farmed
    Presentation given by Prof Mark Costello at the sea lice and sea trout management worskhop at Aultbea Village Hall, supported by WRFT and the Atlantic Salmon Trust, on 20th February 2014. The talk summarise knoweldge of louse biology, transmission to hosts, methods of control and the persistance of the problem. There is also a section at the end about Marine Reserves in New Zealand.  Posted: 24/02/2014 (10.68MB)
  • 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)
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  • 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)
  • 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)