Brown trout are Scotland’s spectacular survivors

By Keith Broomfield
Published on 16/02/2013 14:41

IF you asked me to name Scotland’s most attractive creature, a few years ago my answer would probably have been one of our bird or mammal species, perhaps the kingfisher or red squirrel.

But since taking up fly-fishing my response would now be unhesitating – the brown trout, a fish with the most remarkable range of colours, a feast of vibrant hues and nuances accompanied by a sprinkling of striking blood-red spots.

No two fish are ever the same, and trout from different lochs and river systems also vary in appearance, sometimes quite dramatically. Even within a loch there can be more than one distinct breeding stock. When glimpsed from above swimming under the water it is a drab-looking fish, but in the hand it is transformed into a sparkling jewel. The brown trout is also one of Scotland’s most ubiquitous fish, occurring in the smallest of mountain burns and tarns, as well as in our larger rivers and lochs.

It is those trout in our hill burns and lochans that I find particularly fascinating, with most high-altitude areas having at least some brown trout populations. The Cairngorms is a good example, where trout can be found in steep mountain burns up to 2,800ft. Catching and releasing them on a lightweight rod with a small barbless black fly is wonderful sport and their stunning range of colour more than compensates what they lack in size. But what is especially intriguing is how did these trout get there?

A good example is the hill burn above my house. It is cut off from the rest of the river system by a deep gorge and tumbling water falls, totally impassable to fish. Yet the three-mile stretch of burn in the hills above the falls has plenty of small trout. One can only surmise that despite being only six inches or so in length, these small trout are sexually mature and able to reproduce so as to sustain the population. One also can’t help wondering about the length of time these trout have been left isolated from the rest of the piscine world and whether this means that such populations are genetically unique.

Freshwater fish expert Professor Peter Maitland tells me that while there is no doubt that brown trout have been introduced to a number of high-altitude waters – especially lochs – he is sure that populations in other hill areas, especially burns, are naturally occurring.

“It is most likely that they got there naturally towards the end of the last ice age when our catchments were very different and migratory brown trout and Arctic charr were able to access high waters via ice lakes and other routes available to them at the time,” he says.

“Such populations have thus been there for around 10,000 years. The brown trout is a very flexible species and able to respond to widely different ecological conditions. Some of these small brown trout in upland waters can be quite old, say ten years, and able to spawn at a very small size. Ripe fish as small as 10cm have been recorded at some sites.”

He adds: “Because of their long isolation, some of these populations of brown trout are genetically different from other stocks and are consequently regarded as being of conservation importance. However, in a number of places, conditions are just too harsh for brown trout to maintain themselves, especially some high-altitude lochans where food is scarce and there are no spawning sites available. Such lochans, even those where stock may have been introduced at one time, are fishless.”

Many of our mountain areas hold unique populations of brown trout, some of which are incredibly vulnerable, given the limited area of water catchment where they are found and their susceptibility to some kind of environmental incident. It would be a tragedy if any of these trout communities were lost for good.