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Parasites & diseases

The primary parasite issue in the WRFT area concerns epizootics of sea lice (Lepeophetheirus salmonis) affecting sea trout.

However, other health problems have affected fish: during the 1970s Ulcerative Dermal Necrosis (UDN) affected salmon and sea trout in many rivers within the area. In 2007, many salmon especially grilse had red vent syndrome. Investigations elsewhere indicated nematode worms to be present in affected fish.

Farm fish in Loch Damh were reported to be infected with the viral disease Infectious Pancreatic Necrosis (IPN) on several occasions until the disease was removed from the 'notifiable' diseases list (in 200x). The disease can cause high mortality of farmed salmon smolts following transfer to saltwater. Little information has been seen describing rates of direct (or indirect) mortality of wild salmon or sea trout smolts that carry the virus following entry to saltwater.

WRFT has assisted FRS Fish Health inspectors in collecting samples of salmon parr from the Dundonnell River, Docherty Burn (River Ewe), River Croe and River Elchaig in recent years. Reports obtained have all indicated that no bacterial or viral diseases were detected.

In freshwater, Brown trout are often infected with nematode worms and tape worms. In 2003, WRFT concluded that a principle factor for a lack of larger brown trout in Lochan nam Breac near Gairloch was parasitic infection leading to premature mortality of trout, associated with the seagulls which are attracted to a nearby waste disposal area.

The WRASFB has distributed leaflets and notices wildly within the area it covers warning anglers to take care not to introduce Gyrodactylus salaris. WRFT has distributed information to river areas to the south of the WRASFB area.

Related Downloads

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  • Still too many sea lice?
    Presentation with summary of sea lice problems and results from sea trout sea lice monitoring by WRFT in 2023. Sea lice levels were too high on many sea trout at some sites. The risk of damaging levels of sea lice infestation to emigrating wild salmon post smolts through the Inner Sound may have also been too high. How many grilse will return to rivers in southwest Ross-shire compared to rivers in northwest Ross-shire in 2024? .  Posted: 01/05/2024 (9.90MB)
  • Cryptocotyle lingua (blackspot) on juvenile cod in Loch Ewe, autumn 2022
    A summary of the findings from a coastal fyke net trial by Boor in Loch Ewe within the Wester Ross Marine Protected Area, to monitor sea trout, in autumn 2022. The report describes infestation of juvenile cod, pollack, coalfish and poor cod by the parasitic trematode fluke, Cryptocotyle lingua. .  Posted: 21/11/2022 (803KB)
  • Finding Salmon and Sea trout around the Wester Ross MPA
    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)
  • 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)
  • 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)
  • 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)