Sea Lochs

Scotlands Living Landscapes

• Introduction
• How were sea lochs formed
• What’s special about sea lochs?
• Seashore life
• Rocky shores
• Tidal rapids
• Maerl beds
• Brittlestar beds
• Living reefs
• Seabed life
• Floating life
• Mammals
• Birds
• Sea lochs and people
• Fishing
• Seaweed harvesting
• Fish farming
• Tourism
• Ports and harbours
• The importance of sea lochs
• Threats to sea lochs

What’s special about sea lochs?

The scenery alone, with magnificent mountains descending directly into deep, dark sea lochs, or wide basins freckled with islands and skerries, is enough to mark the west coast of Scotland as a very special place. But there is more to the sea loch story. The deep basins, shallow sills, tidal rapids, plunging underwater reefs and sheltered shores of sea lochs make them very unusual, special habitats for a wide variety of marine life.

Each sea loch has its own unique character. Some of the more complex sea lochs, such as Loch Sween or Loch Maddy (which has at least 22 sills) have many arms, each with their own discrete collection of species.

Because the heads of many sea lochs are extremely sheltered from wave action, we can find a variety of marine habitats quite different to those on the open coast; for example, deep sheltered bedrock and plains of fine mud.

Tidal rise and fall varies from between 1 and 5 metres in different parts of the west coast. Fast tidal currents across the narrow sills reach speeds of 8 – 9 knots (15 – 16 kilometres per hour). These tidal rapids and sounds support a thriving diversity of marine life, sustained by a constant supply of food carried by the currents. Rainfall on the west coast of Scotland is notoriously high, with over 1,000mm per year recorded in many places, much of which eventually runs into the sea. On the open coast this freshwater is quickly mixed with seawater by the wind and waves. But in the sheltered sea lochs, where wave action is slight, the less dense freshwater often floats as a discrete layer on top of the seawater.

In a few lochs, particularly at the top end of the arms of some of the fjards in the Western Isles, lagoons are separated from the rest of the loch by a very narrow, shallow entrance sill which only receives seawater around high tide. These lagoons are permanently brackish and support both fresh and sea water animals and plants. These communities have great natural heritage and conservation value, but are highly specialised and not covered further in this booklet.

The diverse habitats within sea lochs are home to a wide range of species. Over 1,700 species have been recorded in the recent survey of the Scottish sea lochs carried out as part of the Marine Nature Conservation Review. There are probably many more as many of the deepest areas have not yet been sampled.