How do salmon migrate? - UK Youth 4 Nature

Article by Ashvi Daia

Illustrations by Kirsty Lloyd

Salmon Life Cycle

Salmon begin their lives as pea-sized eggs hidden in loose, gravelly riverbed nests in freshwater rivers. When they hatch, they are known as ‘alevins’, ready to embark on their journey through the gravel. First, they must rise to the water’s surface and gulp air to achieve neutral buoyancy, allowing them to swim in fast-flowing streams. Once they can swim freely, they are referred to as ‘fry’.

The fry have eight fins that help them maneuver through the water. As they mature, they undergo a physiological change called ‘smolting’, preparing them for migration to their feeding grounds in the North Atlantic. During this process, their body shape, colour, and behaviour adapt to life in the ocean.

Having reached deep-sea waters, they feed on a diet of crustaceans, sand eels and small fish. However, only about 10% of smolts will survive the numerous predators, sharks, seals, dolphins and humans, and return to the freshwater river they were born in to lay their eggs.

Upon reaching their spawning grounds, the female salmon uses her tail to create a depression in the riverbed, known as a redd, where she lays her eggs. After a male fertilises the eggs, she covers the redd with gravel before moving on to create a new one. During the spawning period, a single female may construct up to seven separate redds and lay between 2,500 and 7,000 eggs!

The spawning process can be so exhausting that over 90% of adults die once the eggs have been laid and fertilised. However, the few that do survive, called kelts, can return to sea and redo this epic journey.

And so, the life cycle begins anew, ensuring the survival of the species for the next generation.

Decline

In Britain, Atlantic salmon are classified as ‘endangered’ by the IUCN Red List, while globally, they are ‘near threatened’ due to significant population declines. These declines are due to a combination of factors, including habitat destruction, pollution, overfishing, climate change, and barriers to migration like dams.

For instance, salmon possess an extraordinary ‘homing instinct’- they can locate the river they were born in using the earth’s magnetic field, the chemical smell of their river, and pheromones. However, water pollution can reduce their ability to locate their river of origin that they need to return to as spawning adults, leading to reduced spawning success and population decline.

It underscores that much more work is needed to improve our natural environment. By reducing our impact on the environment and water, we may be able to reverse the decline of this species.

Not So Freshwater

Our Not so Freshwater campaign is calling on the UK Government to:

Reduce pesticide use by 50% (volume and toxicity) by 2030
Create ambitious targets to restore field margins and riverside ecosystems to reduce field run-off and boost our waters for wildlife and people

If you want to support our campaign, head to our campaign page and write a letter to your MP or subscribe to our newsletter to get regular updates directly to your inbox.

If you’d like to help this iconic species continue to thrive in the UK and across the world, check out our Not So Freshwater campaign page and subscribe to our newsletter to get regular updates directly to your inbox.