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Dimorphic charr population(s) recorded in the lochs of the River Carron system

Posted: Thursday 17 November, 2011 @ 09:11:59

The two mature male arctic charr morphs from Loch Dughaill.

The third WRFT Arctic Charr (& Trout) ‘discovery’ week took place over the week of 31st October – 4th November 2011. Previous charr weeks in 2006 and 2008 have focussed on Loch Maree and nearby waters and charr management. This year, our aim was to learn more about the seldom seen charr of the lochs of the River Carron system. Charr were caught using gill nets. Many of the fish were in colourful spawning condition with bright red-orange bellies; all were photographed and DNA samples taken for analyses.

In one of the hill lochs, charr were found in the absence of trout. There are only a handful of lochs in Wester Ross where charr are present without trout. In the two main lochs of the River Carron system, both trout and charr were caught. At one site in Loch Sgamhain, a trout that regurgitated fish eggs (assumed to be those of charr) was caught along with many charr, suggesting close proximity to a charr spawning area.

Further down the river system in Loch Dughaill, mature male charr were variable in appearance, with at least two distinct male morphs (above). One morph has orange-yellow ventral colouration and a lower jaw that tucks in under the top of the head. Another morph has a bright red-orange belly and a long lower jaw that protrudes out in front of the head. A similar long-jawed male charr was found in the sample from Loch na Sealga.

Morphological divergence and evolution of land-locked populations of charr in post-glacial lochs has been much studied (see references below). Loch Dughaill is a classic example of a relatively small loch with more than one form of arctic charr. Genetic samples taken will supplement those taken by Marine Scotland scientists in July 2008, and may help to explain how morphological variation relates to population structuring.

In terms of freshwater fish biodiversity, Loch Dughaill is one of the richest lochs in NW Scotland. In addition to 2 forms of Arctic Charr, the loch is known to support Atlantic Salmon, Brown Trout (including sea trout), European Eel, Eurasian Minnow and Brook Lamprey. Three-spined Stickleback is assumed to be present.  Sea Lampreys have been recorded in the River Carron just downstream of Loch Dughaill.

Thanks to all for help and support especially Alex Lyle, Ruth Watts (SEPA), Aly Ainsworth, Prof Peter Maitland (for donation of inflatable boat), Richard Wilson, and keepers, Graeme Wilson, Brian Fraser, and Chris ‘Russell’ MacKenzie.

Some references:

  • Anders Klemetsen (2010) The Charr Problem Revisited: Exceptional Phenotypic Plasticity Promotes Ecological Speciation in Postglacial Lakes. Freshwater Reviews 3(1):49-74. 2010
  • doi: 10.1608/FRJ-3.1.3
  • Adams, C.E. & Maitland, P.S. (2007). Arctic charr in Britain and Ireland - 15 species or one? Ecology of Freshwater Fish 16, 20–28.
  • Adams, C.E., Fraser, D., Wilson, A.J., Alexander, G., Ferguson, M.M. & Skulason, S. (2007). Patterns of phenotypic and genetic variability show hidden diversity in Scottish arctic charr. Ecology of Freshwater Fish 16, 78–86.
  • Adams, C.E., Wilson, A.J. & Ferguson, M.M. (2008). Parallel divergence of sympatric genetic and body size forms of arctic charr, Salvelinus alpinus, from two Scottish lakes. Biological Journal of the Linnean Society 95, 748–757.