Freshwater Environments

Scotland's fresh waters - rivers and lochs - are among some of the most beautiful, unspoiled features of Britain today. Scotland has an amazing 30,000 lochs and smaller 'lochans' and 35,000 km of rivers. This is equivalent to 95% of the entire UK's water resources, and covers 2% of the landmass. It is, however, the diversity of these waters as much as the raw statistics that impresses.

 

More than Rivers and Lochs 

Seeps, springs and small burns are abundant in upland areas. To the north and west, the land is drained by numerous small short steep coastal rivers, such as the Shieldaig River.   The east and south of Scotland is dominated by some of Britain's largest rivers - for example, the Tweed, Forth and Tay - with extensive networks of tributaries extending into the heart of the country.

 

In mountainous areas, the diversity of standing waters ranges from small peaty pools to shallow peat-stained lochs, from the small, corrie lochs found high in the mountains to long, deep lochs such as Loch Morar that dominate the glens. Loch Ness holds around one quarter of the total surface water in Scotland, this is twice the surface water of England and Wales combined.

 

In central and southern Scotland, there are large, shallow lochs, such as the Loch of the Lowes, Loch Leven and, straddling both highlands and lowlands, Loch Lomond.   Orkney, Shetland and the Western Isles represent a microcosm of this diversity.

The Diversity of Life

The cooler northern climate, underlying geology and geographic isolation mean Scotland's lochs and rivers often have more in common with those in Scandinavia than the rest of the UK. They are highly distinctive and of international conservation importance.

 

Microscopic plants, or phytoplankton, which when they occur as colonies appear as suspensions of green particulate matter or surface scums, live in the light-filled upper layers of water. Also invisible to the naked eye, are the bacteria, fungi and protozoa that consume dead and decaying organic matter. Higher plants, ranging in type from those that like only their roots in contact with the aquatic environment to those that are completely submerged, occupy the edges of lochs and rivers.

 

Zooplankton, the community of microscopic crustaceans and other animals that live in the water column, can range in size from a fraction of a millimetre to more than 3 mm, and feed on living and dead organic material.   Invertebrates, such as worms and insect larvae dominate life in the loch and rivers sediments. Worms tunnel through the upper layers of the muds, digesting organic matter as it    passes through their bodies, while insect larvae and snails and freshwater mussels feed at the mud/water interface and among the stones.

 

Some 20 species of fish are native to Scotland’s fresh and estuarine waters, while a further 20 or so species have been introduced over the past several hundred years. Species, such as the Atlantic salmon (Salmo salar L.), the eel (Anguilla anguilla), lampreys and sea trout (Salmo trutta L.) (a form of the brown trout (Salmo trutta L.)), are migratory, spending part of their life cycle in fresh water and part at sea.

 

There is a rich diversity within our native species, especially among Arctic charr, brown trout and Atlantic salmon populations. Genetically distinct populations of these fish exist, which over time have become adapted to their specific environment in order to survive. Lochs in the north typically have two to six fish species while  those further south have up to 10. Loch Lomond, however, has more than twice this number due to introductions. Exotic fishes, such as the rainbow or brook trout, come from as far away as North America.

 

Aquatic Food Webs

The plant and phytoplankton communities form the base of the aquatic food web, the complex network of feeding relationships that describes the flow of energy among the various plants and animals that occupy aquatic ecosystems. Plants use the sun’s energy to fix carbon by photosynthesis and dissolved phosphorus and nitrogen to help build proteins. The plants are grazed by zooplankton and by invertebrates, which in turn may be preyed upon by fish.

 

In streams in wooded areas, the energy supply from dead leaves and twigs may be more important than that fixed by the plants. The material is broken down by insect larvae and by the microbial community, again providing food for animals higher up the food web. Most fish feed on zooplankton or invertebrates, although a few, such as the fish-eating ferox form of our native brown trout and the pike, share the top of the freshwater food web with saw-billed ducks and otters and, in our estuaries, seals.

 

Dead plant and animal material is broken down by micro-organisms in the water and muds, thereby releasing nutrients back into the system and providing food for the zooplankton and invertebrates.   Conservation and Exploitation of Scotland’s Freshwater Resources Scotland's cool climate and mainly slow weathering geology means that many lochs and rivers support low numbers of    relatively slow-growing fish. The low nutrient levels and prevailing winds have made areas of Scotland, such as Galloway and the Trossachs, particularly vulnerable to acid rain, which can reduce pH levels in water to such an extent that aquatic life no longer thrives.

 

The geology of lowland areas tends to have softer rocks that yield more nutrients, making them more productive. These areas are where we build our houses and farms, towns and cities. In densely populated and industrialised areas, the way land is used for housing, agriculture, forestry or industry often has a major effect on our fresh waters through, for example, pollution and soil erosion. Water is used by industry, for drinking water supplies, to generate energy and in aquaculture. Abstractions and impoundments have affected fresh waters in many ways, not least by impairing the passage of migratory fish. Many of our rivers and some of our lochs have been impacted in this way, largely to the detriment of fish.

 

Compared with marine fish, freshwater fish are lightly exploited by fishermen. Around half of our species are fished for by anglers, with trout, Atlantic salmon, grayling,  pike,  perch and roach being the most important. As elsewhere in Europe, however, Scotland’s migratory fishes are in decline, with a much smaller proportion of fish returning to fresh waters than was apparent 25 years ago. Various causes have been attributed to the decline of Atlantic salmon and sea trout, including climate change, predation, fish farming and marine fisheries. At both national and international levels, strenuous efforts are being made to investigate and address the issues.

The Status of Scotland’s Fish

While  a number of our fishes in some areas, especially Atlantic salmon, sea trout and eels are in decline, huge investments in the control of pollution and in habitat restoration have resulted in improvements to a number of our fresh waters. The Atlantic salmon has returned to many areas of the River Clyde where it had been absent for decades. Most acidified waters are showing encouraging signs of recovery. The removal of man-made obstacles to migratory fish by the staff of the Tweed Foundation in partnership with local landowners has increased the area of river available to spawning fish, in a local attempt to redress the decline in numbers of Atlantic salmon returning from the sea.

 

Today, there is an unprecedented spirit of cooperation among all interested in the conservation and wise management of Scotland’s fresh waters and freshwater fishes. Association of Salmon Fishery Boards (District Salmon Fishery Boards), Fisheries Trusts (and its coordinating body the Scottish Fisheries Coordination Centre) and fish farmers are working with Government to restore damaged habitats and populations. A number of rivers have been designated    as Special Areas of Conservation for Atlantic salmon lampreys and other freshwater species. The newly introduced European Water Framework Directive introduces the use of ecological measures of environmental quality and integrated management at whole catchment levels. This legislation will ensure that environmental damage is halted and eventually reversed, thereby achieving the objective of sustainable fish populations and fisheries.