The life cycle starts when, in the spring or summer, mature adults return to their river of origin to spawn. The female lays her eggs in the autumn in the gravel bed of the river. Over the winter, the eggs develop into Alevin, and then into Fry. The Fry are mobile and able to escape the gravel bed to feed in the river. Over the summer, they develop into Parr, characterised by their camouflage markings which protect them from predators. In the cooler environment of East Iceland, the Parr typically spend about 3-5 years in the river, reaching 10-12 cm in length. The Parr then transform themselves into Smolts to enable them to leave the river for the richer food resources of the sea. In the “smolting” process, the fish develop a silvery skin and undergo the physiological changes needed to transition into salt water. The “run” of smolts to the estuary takes place in late Spring.
At sea, the Smolts quickly grow from less than 50g in weight to over 2kgs. More than half of the fish mature and return to spawn after just one winter. Others remain at sea for two winters, and in rare cases, three winters.
Spawning salmon do not feed once back in the river. After spawning, they move back to the sea; but because they are exhausted, and hence less able to feed, they are more susceptible to predators and disease. The mortality rate is high at each stage of the cycle.