Atlantic salmon (Salmo salar) can grow up to 30 inches (76 cm) and weigh about 12 pounds (5.5 kg) after spending two years at sea. In four or more years, they can grow much larger, with a record caught in 1960 weighing 109 pounds (49.44 kg). Atlantic salmon migration is an impressive life story.
For four years or more, juvenile Atlantic salmon live in freshwater rivers or streams where they hatched. When the time is right, they undergo a process called smoltification, a complex series of physiological changes that prepare them for life in saltwater. During smoltification, their skin turns silvery and reflective, and their body shape changes. Their gills produce an enzyme that removes sodium from their cells, and various mechanisms are activated to regulate body fluids in the seawater environment.
The first stage of Atlantic salmon migration begins with their journey to the Atlantic Ocean. In the ocean, their diet shifts from primarily insects to larger foods, such as shrimp, eels, squid, and small fish. While in the ocean, they grow faster than in freshwater. After two, four, or more years at sea, something triggers the fish to return to the river where they hatched.
When the salmon reach the river’s mouth, they stop eating and swim upstream. Their primary goal at this point is to return to where their life began. There, they spawn, reproducing to pass on their genes to the next generation. Unlike Pacific salmon, which die after spawning, Atlantic salmon can sometimes recondition themselves to return to the sea and repeat this cycle of migration and spawning. The fact that Atlantic salmon stay in the ocean for varying lengths of time means that a drought in their native river or stream for a year may not halt the reproduction of that year’s salmon.
This impressive life story prompts several questions. How does the Atlantic salmon return to the stream where it hatched? Apparently, they can detect the precise chemical signature of their stream by odor. Another question is why this fish undergoes such a demanding process. Many other creatures in the ecosystems benefit from the salmon’s migration. As predators, Atlantic salmon help control populations of insects in the rivers and smaller fish and other creatures in the ocean. As prey, they serve as food for larger fish, seals, and sharks. They are also valued as a delicious and nutritious food source for humans.
A more challenging question is, how could the impressive life story of the Atlantic salmon migration have happened by chance? We believe it is not by chance. This is more than survival of the fittest; it is a complex system where one animal benefits many others, including humans. Once again, we observe the Creator’s design at work.
— Roland Earnst © 2025