Salmon's Life Cycle

The life cycle of salmon is one of nature's most fascinating stories

Atlantic Salmon have a truly remarkable life cycle. They are 'anadromous' fish which means that juvenile salmon spend their early life in the river before leaving it to feed and grow in the marine environment. When they are mature and ready to mate they return to their native waterway to spawn.

Follow the life cycle on the image below or watch this short video:

Mid-November marks the peak of the spawning activity on the Dee. The female fish, or hen, creates a nest for her eggs, known as a redd. She knocks stones out of her way with her tail to create a depression in the gravel. The males, or cock fish, fight for position and the successful ones move alongside a hen as she deposits her eggs and fertilises them with milt. Using her tail she then covers the redd with stones.

The eggs hatch in the early spring and the small fish known as alevins that hatch still have a yolk sac providing them food for the next few weeks. When the alevins have absorbed the yolk sac and are stronger swimmers they leave the gravel nest and emerge as fry, free swimming, hunting for food and defending a territory among rocks. Once reaching about 5cm in length the fry develop the characteristic thumbprint pattern along their body known as 'parr marks' and are now known as parr.

About 75% of the young fish spend 2 years in the river as fry and parr, 24% stay for three years and around 1% remain for just one year. As they approach the time when they are ready to migrate out to the sea, the parr lose their camouflage bars and undergo a process of physiological changes called smoltification that allows them to survive a shift from freshwater to saltwater. At this point the salmon are called smolts.

Smolts spend time in the brackish waters of the estuary while their body chemistry adjusts to the higher salt levels they will encounter in the sea. Smolts also grow the silvery scales which visually confuse predators- although they still suffer heavy losses during the early phase of migration.

The Dee’s smolts begin their journey in early summer and it is common to see them as the move downstream to the sea where they migrate to feeding grounds in the ocean. Salmon from the River Dee and other Scottish rivers generally migrate to grounds off the South West Greenland coast, the Faroe Islands, into the Norwegian Sea or to waters off North West Scotland.

The journey to SW Greenland is a long one – 1500 miles each way – and the salmon that undertake that journey spend at least two winters at sea. On their return to the river they are called Multi Sea Winter (MSW) salmon, normally abbreviated to ‘salmon’. Of the fish that feed off of the Faroe Islands and NW Scotland, some will spend two Winters at Sea (2 SW) and return as salmon, but others will spend only a single winter at sea, particularly those feeding off the Scottish coast. These one Sea Winter (1 SW) fish are termed grilse. Approximately half of the rod-caught fish on the Dee in the summer and autumn periods are grilse. Grilse tend to be dominant in the Dee’s rod catch in the months of August and September, are present in high numbers in July and October and present in low or very low numbers between April and June. Spring salmon and salmon caught in the Upper Dee have spent 3 years in the river as a juvenile. This is likely to be because the number of years taken to reach the smolt stage is influenced by feeding opportunities, climate and weather conditions, making growth harder in the upper catchment.

The River Dee Trust uses the scales of fish to reveal an insight into their life. Salmon scales show how many years the fish has spent at sea, how many in the river as a juvenile, and if it has spawned previously. In addition, scales indicate approximately when the fish entered the river as an adult. We read the scale in much the same way as you can tell the ages of a felled tree by counting the growth rings in a the trunk. This information is obtained through a scale sampling programme on the River, carried out by the Trust and relying on help from ghillies and angling club representatives who collect scales from approximately 10% of the salmon caught on the Dee.

Want more? Explore further in our Education section or watch ‘To The Journey's End: The Life cycle of the Atlantic Salmon’ which features salmon footage shot in the Dee and Don among other northeast Scotland rivers.

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January 30, 2020

The River Dee Trust has announced plans to plant a million native trees in one of the biggest nature restoration projects in the Cairngorms. The project will recreate areas of landscape that have been lost for 2000 years.

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