Native Freshwater Fish in South-West Scotland: impact of environmental changes

At its meeting on 19th October, the Dumfriesshire and Galloway Natural History and Antiquarian Society enjoyed a talk entitled Native freshwater fish in south-west Scotland: Impact of environmental changes given by Andy Ferguson, Professor Emeritus, School of Biological Sciences, Queen's University Belfast.

He began by noting the past interest in freshwater fish by the society. The first president Sir William Jardine was known for his work on the subject and over the years the Transactions of the society had included various papers on the topic including several by Peter Maitland, the renowned fish conservationist.

He went on to define native freshwater fish as having colonised naturally after the retreat of the ice sheet at the end of the last ice-age and included any species that spent at least part of its life cycle in freshwater. In south-west Scotland native species are restricted to the salmonid family, smelt, shads, lampreys, eel and sticklebacks. He highlighted that freshwater fish are the most endangered group of vertebrates worldwide with 30% of species threatened with extinction. Multiple factors are involved in their decline, with some of the main ones locally being acidification of the water as a result of burning fossil fuels, afforestation, enrichment and pollution, hydroelectric and other dams and the introduction of non-native species.

The salmonid family of vendace, Arctic charr, Atlantic salmon and brown trout formed the main focus of the talk.

The vendace, the rarest native freshwater fish in Britain, which had been present in the Castle and Mill Lochs at Lochmaben is now extinct there. No vendace have been recorded at Castle Loch since 1912 possibly due to enrichment from new sewage works in 1911. There have been no vendace from Mill Loch since 1970, probably due to several factors including enrichment from surrounding land and the introduction of non-native bream. A decline in Cumbrian vendace led to their being introduced into lochs in south-west Scotland as refuges. Loch Skeen near Moffat now has a thriving population of fish originally from Bassenthwaite.

Arctic charr used to be in Loch Grannoch and Loch Dungeon but are now only definitely known in Loch Doon, although in reduced numbers. Acid precipitation leading to acidification of the water is thought to be behind their decline. Conservation refuge populations were successfully introduced into the Talla and Megget reservoirs in the late 1980s.

Atlantic salmon are present locally in all larger rivers but in much reduced numbers compared to the past. They return from feeding around the Faroe Islands and western Greenland to their home river with a high degree of accuracy, which results in each river having genetically distinct populations. The decline in numbers can be due to changes in the rivers, such as dams which prevent the fish from reaching their spawning grounds, but marine survival has also declined. Food availability at sea can be affected by an increase in sea temperature and changing currents. There is also the problem of parasites such as sea lice from salmon farms which can lead to high mortality in wild salmon and interbreeding with farm escapees which leads to a reduction in the fitness of the wild salmon. Since 2016 Marine Scotland has introduced restrictions on estuary netting and at present 70% of Scottish rivers, in our area the Fleet, Bladnoch, Annan and Dee for example, can only be fished on a catch and release basis in an effort to halt the decline.

Brown trout are present in many lochs and rivers in south-west Scotland, but their numbers have been adversely affected by acidification and the consequent rise in aluminium to toxic levels in the water, especially in the latter part of the 20th century. Loch Enoch was the first to be affected with trout becoming extinct there by the 1920s. Surveys in the late 1970s found low numbers of, or no trout, in lochs where they had been present in the 1950s. International action to address the problem of acidification in the late 1980s and 1990s led to a decrease in sulphur and nitrogen emissions which resulted in the pH levels increasing, and in lochs where trout had survived, numbers rose rapidly.

The area surrounding Loch Fleet was limed in 1986–87 and an improvement in pH resulted so that it could be restocked.

Brown trout vary considerably in appearance and have become the model species for scientific work, the focus of which is to conserve the genetic biodiversity represented by the various populations. The years 2010–13 saw the Galloway trout study undertaken. The trout in Loch Grannoch have been found to be genetically unique and have a genetically-based tolerance of low-pH/high-aluminium level. Trout from Loch Grannoch have been introduced successfully into lochs where previously no trout survived, such as Loch Enoch. Professor Ferguson would like to see Loch Grannoch established as an SSSI or other type of reserve.

The non-salmonid native freshwater fish species were then mentioned.

Smelt, which smell like cucumber, live in coastal waters and enter rivers to spawn. They used to be in all of the larger Solway rivers but are now only found in a short stretch of the River Cree. They used to be an important fish locally but numbers have declined since the 1980s. The Galloway Fisheries Trust is monitoring smelt in the Cree as part of the 'Saving the Sparling project'.

The shads, allis and twaite, were formerly known to spawn in Solway rivers, but there is no recent evidence of spawning.

Solway rivers contain all three species of lampreys, brook, river and sea.

The European eel was formerly abundant, but numbers have declined in recent decades and it is now considered to be critically endangered.

All native freshwater fish species in south-west Scotland have declined, with only the brown trout showing a good recovery post-acidification. Many of these fish species have been socially and economically important to local communities and businesses in the past, but even in the present, Atlantic salmon and brown trout anglers contribute large amounts annually to the local and national economy.

In conclusion, future challenges to native freshwater fish survival were listed, so continued monitoring is required.

A.C.