The salmon run: an autumn ending to a long journey

Each year, Atlantic salmon make an incredible journey back from the ocean to return to their breeding grounds. To get there, this mighty fish propels itself, like a dart, up and over the fast-flowing waters of some of our finest rivers in Scotland.

A male Atlantic salmon leaping up a waterfall, River Almond. Copyright Lorne Gill/NatureScot

At a cascade where salmon gather, their jumping against the flow can seem little short of miraculous. October is the peak season for Atlantic salmon moving upstream in over 350 of Scotland’s river systems.

On many rivers, waterfalls are obstacles that must be overcome if they are to return to their gravel bed spawning grounds. This gives us a unique opportunity to see this epic struggle as they launch themselves high through the air in a determined effort to clear the barrier in one tremendous leap. It can take many attempts before they make a successful jump, as many fall short or crash off the rocks that block their way. However some fish can get it right first time and soar majestically upstream in one perfect leap.

Atlantic salmon are found in the temperate and arctic regions of the northern hemisphere. They occur in the rivers of the countries that border both sides of the North Atlantic Ocean, and the Baltic Sea. Scotland is blessed with both many waterfalls and many salmon rivers. It is also unusual in having salmon that enter its inland waters most months of the year. This includes a sizeable ‘autumn run’ of fish, which often peaks this month in October.

People watching as Atlantic salmon migrate up the River Almond.
©Lorne Gill/SNH/2020VISION

As an anadromous species, Atlantic salmon live in freshwater as juveniles but migrate to sea as adults before returning up river to spawn. Atlantic salmon return to their native river, and even the same stretch of the river from which they were born, with amazing accuracy. This means that many ‘populations’ of Atlantic salmon may exist within the same river.

Spawning usually occurs from November to December, but may extend from October to late February in some areas, particularly larger rivers. About 90 to 95% of all Atlantic salmon die after spawning has taken place. Those that survive may spawn again.

Female fish lay their eggs in gravel depressions known as ‘redds’. As a female releases her eggs, an adult male or mature juvenile immediately fertilises them. The female then covers the fertilised eggs with gravel.

Hatched Atlantic aalmon egg at the Tay District Salmon Fisheries Board Hatchery at Almondbank.©Lorne Gill/NatureScot

How long it takes for eggs to hatch depends on water temperature. Eggs will usually hatch in early spring. Once the fish have developed markings on their sides, they’re known as ‘parr’. The parr will live in the river for two to three years, depending on water temperature and food availability. On reaching about 12cm in length, the parr undergo a physiological transformation that lets them survive at sea.

The young fish, now called ‘smolts’, continue to change in appearance, becoming silver. These ‘post-smolts’ begin to leave rivers for the sea in late spring, with most fish gone by June.

We still don’t know much about the migration pathways of post-smolts or returning adults. Some research has shown that post-smolts move in schools when heading to deep-sea feeding areas. Some of these fish feed in the Norwegian Sea and the waters off southwest Greenland. These fish remain in the ocean from just over a year to three or four years.

Of course, many of us haven’t been able to get out and enjoy the salmon run this autumn, but luckily our photographer, Lorne, has put together this wonderful video – we hope you enjoy it!

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