Atlantic Salmon (Salmo salar): Life Cycle, Facts and Range

What does an Atlantic salmon look like?

At sea, an adult Atlantic salmon is a streamlined, torpedo-shaped fish with a small pointed head, a blue-green or brownish back and bright silver sides and belly. Black spots, often shaped like a small X or cross, are scattered mostly above the lateral line, the faint line along each flank that senses movement in the water. The tail is only slightly forked and usually has few or no spots.

Young salmon look quite different. Parr, the stage that lives in rivers, are brownish with 8 to 11 dark smudges along each side, called parr marks, and a row of small red spots. This pattern hides them well against gravel and stones.

When adults come back to fresh water to spawn, they slowly lose their silver shine. Both sexes turn bronze, brown or purplish, often with red or orange spots. Males grow a hooked lower jaw called a kype, which they use when fighting rival males. After spawning, the exhausted fish are thin and dark, which is why kelts have been called “black salmon”.

Atlantic salmon are easily confused with sea trout, the sea-going form of the brown trout. In a salmon, the upper jawbone ends about level with the back of the eye, while in a sea trout it reaches beyond the eye. A salmon also has a narrower “wrist” just in front of the tail.

How big do Atlantic salmon get?

An Atlantic salmon’s size depends mostly on how many winters it has spent feeding at sea. Fish in the same river can differ greatly in size because some return after one winter and others after two, three or more.

Truly giant salmon are rare. The heaviest reliably recorded fish weighed about 49 kg (109 lb) and was taken in a net in the estuary of the River Hope in northern Scotland in 1960. The rod-caught record is a fish of about 36 kg (79 lb) from the Tana River in Norway. Britain’s rod record, a fish of 29 kg (64 lb), was landed on the River Tay in 1922 by Georgina Ballantine.

Habitat and range

The Atlantic salmon breeds in rivers that flow into the North Atlantic and the Baltic Sea. In Europe, it ranges from northern Portugal and Spain through France, Britain, Ireland, Scandinavia, Finland and the Baltic countries to the Pechora River in northwest Russia, and it also breeds in Iceland. In North America, it breeds from Maine through the Canadian Maritimes, Quebec and Newfoundland to Labrador and Ungava Bay, and a single native population lives in western Greenland.

Salmon rivers need cool, clean, well-oxygenated water and loose beds of gravel and cobbles. Eggs and young fish die quickly if silt clogs the gravel or the water becomes too warm or polluted. At sea, Atlantic salmon prefer water of roughly 4–12 °C (39–54 °F).

Some populations never go to sea at all. These landlocked salmon spend their whole lives in large lakes and the rivers that feed them, for example Lake Vänern in Sweden, Lakes Ladoga and Onega in Russia, and lakes in Maine, Quebec and Labrador, where they are often called ouananiche.

Life cycle: from egg to kelt

The life of an Atlantic salmon has more named stages than almost any other fish.

1. Eggs. Spawning happens from October to January. The female digs a nest called a redd by beating her tail against the gravel, and lays her eggs in pockets 10–25 cm (4–10 in) deep while a male fertilizes them. She lays about 1,500–1,800 eggs per kilogram of her body weight (700–800 per pound), so a 5 kg (11 lb) female may lay 7,500–9,000 orange, pea-sized eggs.
2. Alevins. The eggs hatch in early spring. The tiny alevins stay hidden in the gravel for several weeks, living on the yolk sac attached to their belly.
3. Fry and parr. In spring, the fry wriggle out of the gravel and start feeding. They soon become parr, which spend 1–4 years in the river, and up to 8 years in the coldest northern rivers.
4. Smolts. When parr reach about 12–20 cm (5–8 in), they turn silver and go through smoltification, a set of body changes that lets them survive in salt water. Smolts swim downstream to the sea, mostly between April and June.
5. Life at sea. Salmon spend 1–4 years at sea, growing quickly. Grilse come back after one winter, while multi-sea-winter salmon stay longer and return bigger.
6. Spawning and kelts. Adults return to their home river, stop eating and spawn in late autumn. Many die afterward, but some survive as kelts, drift back to sea and may return to spawn again, usually only once more.

Some male parr mature in the river without ever going to sea. These “precocious” males, often just 10–15 cm (4–6 in) long, sneak in beside spawning pairs and fertilize some of the eggs.

What do Atlantic salmon eat?

In rivers, young salmon are insect-eaters. Fry and parr feed mostly on the larvae of mayflies, caddisflies, stoneflies, blackflies and midges, plus land insects that fall onto the water in summer.

At sea, salmon become active predators. Post-smolts eat krill, amphipods and small fish larvae, and older salmon hunt fish such as capelin, herring, sand eels and young cod. The pink color of wild salmon flesh comes from astaxanthin, a natural pigment in the shrimp-like crustaceans they and their prey eat.

Adult salmon stop feeding once they enter fresh water to spawn. They live for months on fat and muscle stored at sea, which is one reason spawning is so exhausting.

Migration and homing

The Atlantic salmon is one of the great long-distance travelers among fish. Smolts from European rivers head north into the Norwegian Sea and around the Faroe Islands, while many multi-sea-winter fish from both Europe and North America feed off West Greenland and in the Labrador Sea, thousands of kilometers from home.

Most return with remarkable accuracy to the river where they hatched, and usually to the same part of it. Scientists think salmon use Earth’s magnetic field to steer across the ocean and then follow the remembered smell of their home river. The details are explained in How do salmon find their way home?

The journey upstream can involve rapids, weirs and waterfalls. Salmon have been recorded leaping up to about 3.65 m (12 ft), although most jumps are much lower. For more on this part of their lives, see Why do salmon swim upstream? and our list of the longest animal migrations.

Lifespan

Most wild Atlantic salmon live about 3–8 years in total. A typical fish might spend two or three years in the river and one or two at sea before spawning at four or five years old. Fish from far northern rivers, where parr grow slowly, and salmon that spawn more than once live longest, with ages of about 13 years recorded.

Predators and threats

Young salmon have many enemies. Brown trout, eels, pike, herons, kingfishers, goosanders, cormorants, Eurasian otters and American mink all eat eggs, parr or smolts. At sea, post-smolts are taken by seabirds and larger fish, and adults are eaten by gray and harbor seals and by large predatory fish.

Today, the biggest threats come from people. Dams and weirs block rivers, while pollution, farm runoff and silt smother spawning gravel. Changes in the ocean, including warming, appear to have cut the survival of salmon at sea since the 1990s, and fewer young salmon now return as adults than in the 1970s and 1980s.

Salmon farming adds further pressure. Salmon lice (Lepeophtheirus salmonis), a parasitic copepod that builds up around open-net farms, can kill migrating smolts, and escaped farmed salmon breed with wild fish and weaken their local adaptations. In Norway, the introduced parasite Gyrodactylus salaris has devastated salmon in dozens of rivers, and invasive pink salmon from the Pacific are now spreading along northern European coasts.

Conservation status

The IUCN Red List moved the Atlantic salmon from Least Concern to Near Threatened in 2023, after new evidence showed the global population fell by about 23% between 2006 and 2020. The species now survives in only a small part of the rivers it inhabited a century ago.

Some populations are in far worse shape. In the United States, the Gulf of Maine population, the last wild sea-run Atlantic salmon in the country, has been listed as endangered under the Endangered Species Act since 2000. In Canada, the Inner Bay of Fundy population is also listed as endangered. The full picture is covered in Are Atlantic salmon endangered?

Conservation work includes removing dams, building fish passes, restoring riverbanks, limiting fishing at sea through the North Atlantic Salmon Conservation Organization (NASCO), and moving salmon farms to closed systems.

Myths and facts

Myth: all salmon die after spawning. This is true of most Pacific salmon, but not of Atlantic salmon. A minority of Atlantic salmon survive, return to sea and spawn again. See Why do salmon die after spawning?

Myth: farmed salmon is dyed pink. Farmed salmon are not painted or dyed after harvest. Instead, astaxanthin, the same pigment wild salmon get from crustaceans, is added to their feed.

Myth: salmon feed on their way upstream. Returning adults stop eating in fresh water. They may snap at objects in the river out of habit or aggression, but they do not need food until they return to sea.

Fact: the name means more than “salmon”. Salar is often translated as “leaper”, a fitting name for a fish that jumps waterfalls, though the word’s true origin is uncertain. Salmon have been prized for thousands of years, from the Irish legend of the Salmon of Knowledge to the river laws of medieval Scotland. Today, almost all Atlantic salmon eaten around the world is farmed, while wild fish are mostly protected.