In November Wester Ross Fisheries Trust hosted a sea trout and arctic charr discovery week in the Carron catchment. The aims of the week were to try to assess the arctic charr populations in the catchment and to assess how far up the river sea trout were travelling to spawn and also the extent to which they were using the two large lochs, Dughaill and Sgamhain.
The week was a great success, recording good populations of charr in Loch Dughaill, where two different forms were thought to exist, and also in Loch Sgamhain where they have not been recorded for some years. They were also found in a loch high in the hills where they had never previously been recorded.
Arctic charr are of great interest to biologists. In contrast to other populations around the world Scottish populations are non-migratory and have been isolated in their lochs since the ice age, leading to differentiation between populations, much like Darwin’s finches. They even form different populations within single lochs, and it is thought that the surface feeding, pelagic fish and bottom feeding benthic fish in lochs such as Dughaill may be separate populations, showing genetic and morphological differences. They are thought to be particularly vulnerable to global warming and acidification, and despite North-West Scotland being one of their strongholds, their distribution is largely unknown.
The discovery week also helped illuminate the ways in which sea trout use the Carron catchment, and sea trout and finnock were captured in fyke, sweep and gill nets in Lochs Dughaill and Sgamhain. Fyke nets at the very top of the catchment captured fish which appeared to have been to sea and returned to spawn (pictured below). Scale analysis will hopefully reveal whether these large fish have migrated to sea or grown large feeding in the lochs for several years.
In 1936 and 1937 G. Herbert Nall assessed the sea trout population of Loch Dughaill, capturing in excess of one thousand fish. Wester Ross Fisheries Trust swept one of the bays used in Nall’s study and were pleased to record numbers of finnock and sea trout at the lower end of the loch. It was noticeable that a high proportion of these fish were immature finnock (pictured below), which may over-winter in the loch before returning to sea to feed in the spring. Scale samples were taken from all trout and will be analysed over the winter to try to assess which fish were genuine sea trout and which were loch trout.
