Case Study: Salmon Life Cycle

Salmon hatch and die in fresh water, but they live their lives in salt water. Salmon rely on both fresh and salt water to complete their full life cycle.

These dynamic fish are born in freshwater rivers, and they spend the beginning of their lives nestled close to the gravel and rocks on the river's bed to protect themselves from the water currents above. After about a year of living and growing in the river, the young salmon follow the river downstream and swim into the open ocean. Before the young fish enter the ocean, however, they must swim through an estuary.

Estuaries are where freshwater rivers and salt water from the ocean meet. The estuary allows the young salmons' bodies to adjust to saltwater conditions. In addition, the abundant food in an estuary allows the fish to eat as much as they can to help them survive their transition into the open ocean.

Depending on the species, salmon can spend one to 8 years in the open ocean growing to full adulthood. When it is time to mate, adult salmon swim back to the same river that they hatched in. Since they will be transitioning from salt water back to fresh water, they must again stay in the estuary until their bodies are ready for freshwater. Then, they swim upstream against the river's current to return to their hatching place.

The female salmon lay their eggs underneath the gravel where the eggs stay until they are ready to hatch. Shortly after laying and fertilizing all their eggs, both the male and female salmon die, and the life cycle begins again.

The complex life cycle of salmon is just one example of how important both fresh and salt water are to supporting life on Earth.