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Kinlochewe workshop provides new information on wild trout diversity in the Loch Maree catchment area

Posted: Tuesday 28 May, 2019 @ 11:04:19

Counting sea lice on a sea trout sampled from Flowerdale estuary on 1st May 2019

Supported by The Wild Trout Trust, Middlesex University, Wester Ross Area Salmon Fishery Board, UHI Rivers and Lochs Institute and Marine Scotland Science.

The recent Wester Ross Wild Trout workshop provided a long awaited opportunity to learn of the outcome of several recently completed investigations which focussed on the genetic diversity of wild trout within the Loch Maree catchment area. The main purpose of the workshop was to provide an opportunity for Dr Steve Kett of Middlesex University and his research team to return to Wester Ross to report their findings following over 12 years of sampling within the Gairloch area and follow up lab work. We were also delighted to welcome Prof Eric Versoor (UHI Rivers and Lochs Institute), Dr Dave Morris (Marine Scotland Science) and Gareth Pedley (Wild Trout Trust Conservation Officer for N England and Scotland) to present talks.

Dr Steve Kett (Middlesex University) introduced the Loch Maree Wild Trout Project.  Launched at the Loch Maree Hotel (‘anglers Mecca of yesteryear’) in 2007, objectives included unravelling the genetic diversity of wild brown trout (including sea trout) within the Loch Maree catchment area for the purposes of informing conservation and fisheries management. Samples of both brown trout (non-seagoing) and anadromous trout (sea trout) were collected from isolated hill lochs high in the hills, spawning streams accessible to sea trout around Loch Maree and other lochs, river estuaries and coastal seas.  Funding for analyses included biomedical research grants (with regard to parasite research trout can be useful proxies for people) and other providers not normally associated with trout research. Some of the material collected also provided novel opportunities for student teaching.    

Vu Dang’s talk (from Middlesex University MScRes project) was entitled ‘A first look at the population structure of Loch Maree wild trout’. 192 samples of trout taken from 35 sites within the Loch Gairloch to Loch Maree catchment area were analysed. The results suggested that the trout population decline associated with the collapse of the sea trout fishery may have caused a genetic bottleneck. Samples of sea trout from the Gairloch and the NW Loch Maree area showed the greatest similarities and overall diversity; suggesting large overlapping coastal ranges of different populations. This finding implies that sea trout from different spawning populations mix together as they move around the coast in their search for food before returning to spawning streams. Genetic divergence of resident trout populations correlated with geo-hydrological distance (distance ‘as the fish swims’). For example samples of trout from headwater streams were least similar to those taken close Poolewe. However, there was also evidence of some introgression between populations, suggesting some straying and interbreeding of trout in different populations at spawning time. Trout from streams and lochs above impassable barriers had the least genetic diversity.  Vu suggested that all the trout were descended from an ancestral sea trout population rather than from trout that had remained in freshwater during the ice age. In terms of management, protection of headwater trout populations within the area accessible to sea trout would have conservation benefits all the way downstream. Vu’s presentation can be found here:

The Brown trout (Salmo trutta) is an intermediate host for many parasites.  Heavy parasite infestation of wild trout can limit fish size and age. Dr Toby Landeryou’s talk (from Middlesex University PhD studies), entitled ‘Immunogentic adaptation of UK brown trout population to parasite infection’, focussed on samples of trout from 14 hill lochs in the Gairloch area. A total of 2143 parasites were dissected from 210 trout. Three types of parasite were found.  Cestodes (tapeworms) were present only in three lochs including Lochan na Breac in the northwest of the study area. Nematodes (roundworms) were recorded only in samples from two hill lochs in the middle of the study area. However, trematodes (eye flukes) were found in trout sampled in 13 of the lochs. Eye flukes cause cataracts; heavily infected trout have compromised eye sight. From genetic analyses, eye flukes were identified as belonging to the Diplostomum baeri species complex.  Gairloch trout had greater D. baeri genetic diversity than those sampled on the European mainland and in Iceland. As the life cycle of Diplostomum includes birds such as divers and gulls; bird migration provides an explanation of observed diversity. Three species of cestode (tapeworms) were identified, including Diphyllobothrium spp. We were reminded that wild fish should be thoroughly cooked; one of the Diphyllobothrium species recorded can infect humans.  The next part of the study focussed on finding out whether any of the hill loch trout populations had developed genetic immunity to parasites?  Analysis of a genetic complex linked to parasite infestation [Satr-DAB] demonstrated clear inter and intra-population diversity. There was greater diversity in lochs where cestode infestation occurred, implying selective potential, and the potential importance of adaptation to local environmental pressures within trout populations. Such information is of relevance to possible stocking programmes; trout from populations which have not encountered the parasites before may do less well as those from populations which have evolved in an environment where parasites are present.

Prof Eric Verspoor (UHI Rivers and Lochs Institute) talk ‘The diversity of lacustrine brown trout in Scotland’ included a summary of the recently published and widely reported Loch Laidon trout diversity study . Loch Laidon is located near Rannoch Moor in the Central Highlands. Genetic analyses of samples collected using gill nets set at different depths in the loch had revealed the presence of four different forms of trout, each belonging to a discreet population. Each form of trout was found to occupy a different habitat with different ecology within the loch. One of the forms had an unusually large eye relative to other trout in the loch. It was found in the deepest water, occupying habitat usually associated in other Highland lochs with benthic arctic charr. This was the first time a profoundal benthic form of trout had been reported from a lake in Europe; highlighting how little is known about population diversity of wild trout.  Genetic analyses of samples of trout taken from different depths in Loch Maree using gill nets suggested that there were also four different populations within Loch Maree, or perhaps as many as 10 trout populations! Further work including additional sampling of trout in Loch Maree [where two forms of arctic charr are also present] is required to learn more about the differences in the morphology and ecology of trout.

Following the lunch break, Peter Cunningham (SWRFT Biologist) presented a talk entitled ‘Wester Ross: a stronghold for the future of wild brown trout?’. Examples of the diversity of wild trout (with illustrations by Paul Vecsei ‘Fish as Art’) and their habitats within the area were shown. There was much variation in size at maturation, shape, colour and ecology of trout. The appearance of trout caught in the Fionn Loch suggested complex population structuring. Within the Loch Maree catchment, were ferox trout which grow to over 4kg, sea trout (to over 9kg) and various isolated hill loch and hill stream trout growing to no more than 100g. Sea trout had been sampled by SWRFT in estuaries, off sandy beaches, over seagrass beds and were known to utilise other habitats. In years with abundant sandeels, sea trout grew rapidly during the early summer attaining condition factors of over 1.4 by early July (e.g. 2009). In other years (e.g. 2010) growth was much less. Some individual trout, recognised by their spot pattern, had been recaptured several times at the same location. Sea lice infestation associated with salmon farming remained a major concern. A sample of 30 trout from the Flowerdale estuary, Loch Gairloch in April 2019, carried an average of over 100 lice. Similar infestations were recorded at the same location in springs of 2017 and 2015. In spring 2015 heavily lice-infested trout were also recorded around Loch Torridon; correlating with the period when salmon farms within the loch had reported high numbers of lice. In autumn 2015 trout were sampled in a spawning stream in the Torridon River system. This demonstrated that despite high sea lice infestation pressure in nearby waters, the adult trout population was still dominated by repeat spawning adult female sea trout and adult male sea trout; several fish of over 45cm were recorded. This was contrasted with the lower survival and smaller size of adult sea trout entering the Shieldaig River system in outer Loch Torridon during the period up to 2012, hinting that the occurrence of some areas of shallow fresh or brackish water in some upper sea lochs may provide localised protection for some trout populations from sea lice infestation. Peter’s presentation can be found here:

Dr David Morris (Marine Scotland Science) provided a summary of some of the research at the nearby MSS Shieldaig Field Station by Loch Torridon and an introduction to the Loch Torridon sea trout and salmon tracking project. To obtain large enough numbers of emigrating sea trout (smolts) for research purposes, a long-term stocking programme had been carried out in the River Shieldaig system. Results from fish trap studies indicated a pattern where higher numbers of sea trout returned following the 1st year of the farm salmon production cycle in Loch Torridon than in the second year of the cycle.  To learn more about the behaviour of sea trout in Loch Torridon a sea trout and salmon smolt tracking project began in 2018. Smolts were caught on their way downstream in the river Shieldaig system, and in the Balgy and Torridon rivers. Those over 135mm were fitted with an acoustic tag. Two different types of tag were used. 79 receivers for detecting the nearby occurrence of tagged fish were located within the loch. Various challenges regarding receiver separation and tag detection distance were considered including trials to find out how far and in what sea conditions (and anthropogenic noise levels) tagged fish would be detected. Initial results from the tracked fish were shown by way of an animation. Tagged sea trout smolts displayed many different behaviours moving to and from and within large parts of upper Loch Torridon. This work is on-going.   

Dr Martijn Timmermans (Middlesex University) described how the sea louse (Lepeophtheirus salmonis) can be used for teaching students about natural selection. Parasitic sea lice have been a major health concern for farmed salmon for many years. To control on-farm sea louse infestation, several pesticide treatments including bathing salmon in organophosphate solution had been used. However sea lice had developed resistant to some of the pesticides, making treatments less effective. Kaur et al. 2015 had investigated the mechanism behind resistance in salmon lice against the organophosphate pesticide ‘Azamethiphos’ and identified the associated genetic mutation. It was now possible to screen sea lice to find out whether or not they carried this genetic mutation for organophosphate resistance. Fjortoft et al. 2017 demonstrated widespread distribution of organophosphate resistant lice around Norway. A small number of sea lice were collected from wild sea trout and salmon around Wester Ross for teaching purposes. Lice from the sea trout were also found to have the genetic marker for organophosphate resistance. However those taken from wild salmon did not have the associated genetic mutation.

Gareth Pedley (The Wild Trout Trust) described some examples of habitat problems and solutions along some of the wild trout streams elsewhere in Scotland and NW England. The Wild Trout Trust provides targeted advice for wild trout conservation and management, and supports habitat restoration projects in partnership with many other groups or organisations. Common problems include siltation of spawning gravels associated with soil and river bank erosion sometimes linked to grazing pressures from livestock, stream widening and a lack of riparian vegetation. Leafy riverbanks especially those with some tree cover are best for protecting river channel morphology and for providing food for the insects upon which trout feed.  A range of examples of interventions to restore or improve trout habitat were shown some. Similar interventions may benefit wild trout [and juvenile salmon production] along many of the streams within the Wester Ross area. Gareth’s blog can be found here.

Thank you very much to Dr Steve Kett, colleague Dr Martijn Timmerman and post-graduate students Vu Dang and (Dr) Toby Landeryou of Middlesex University for much work over many years analysing samples of trout collected from lochs and rivers around the Gairloch area, and to Prof Eric Verspoor, Dr Dave Morris and Gareth Pedley for supporting the workshop.  Thank you to everyone for coming along and especially to Dr Pat Brunton for delivering lunch!

For workshop field trip on 1st May we met in the SWRFT office in Gairloch. Subsequently we were able to catch 2 sea trout using a sweep net in the Flowerdale burn estuary nearby. One of the sea trout carried 560 sea lice. Then we set off to explore some of the wild trout waters in the hills above Gairloch; using an assortment of sampling equipment specifically designed for such purposes.  Congratulations to Martijn T for catching his first wild brown trout in Scotland, and to mentor Dr Steve Kett. Thank you to all the other helpers especially Nick Benge, Chris Beresford, Prof Eric McVicar, Alasdair Macdonald, the Middlesex University team and a film crew from Scottish Television for recording the event.