Salmon are very well-known fish that many people and animals eat. They are famous for their journey back to their birthplace to reproduce. Salmon are native to the Pacific and Atlantic oceans, as well as any rivers that empty into the oceans. There is only one species of salmon in the Atlantic, the Atlantic Salmon, while many different species live in the Pacific. An anadromous is a salmon that goes through the entire life cycle, including their memorable journey back to the spawning grounds.
Atlantic salmon start out as tiny eggs that are buried with loose gravel in a river that leads into the Atlantic Ocean. Eventually, alevins (just-hatched salmon) emerge from the eggs and start to swim up through the gravel. Once they are free of the gravel, the alevins are called fry. They have fins and eat microscopic invertebrates. In the fall, they change to parr. Parr have vertical stripes or spots for camouflage and grow to about 10-25 cm within 1-3 years. Then they turn silver, adapt to seawater, and become smolts that head to the Atlantic Ocean. While there, they eat sand eels and different fish such as herring. A grilse is an adult salmon that reaches maturity after about one year at sea, but some salmon take 2+ years. Matured salmon start to return to their birthplace.
Adult salmon are able to find their birthplace by using their incredible “homing instinct”, much better than any human’s sense of direction. They are able to perfectly pinpoint their spawning grounds from over 3,000 km away, guided by Earth’s magnetic field, the chemical smell of the river, and pheromones from other fish. As the salmon head upstream, they must get by waterfalls, dams, and, of course, the current of the river (check out this video for salmon jumping up waterfalls! https://youtu.be/j5pTnejk4s4). Limiting factors such as fishermen, poachers, pollution, and predators also challenge the fish. In addition, the salmon haven’t eaten since leaving the ocean, so they are weak from hunger. The salmon cover their eggs with gravel to protect them from predators. Those who managed to get back to the spawning grounds and successfully spawn are called kelts. Their weakness makes it much easier for predators to catch them, so many salmon don’t survive after spawning. However, some manage to go back to the ocean and repeat the process.
SOURCE: https://www.marine.ie/Home/site-area/areas-activity/fisheries-ecosystems/salmon-life-cycle
