In the case of the salmon this homing instinct is so acute that it returns to the proper site after four or five years of living at sea. While at sea, salmon eat shrimp, crabs and other marine invertebrates, storing energy for the long migration and period of fasting while in the rivers. Formerly plentiful throughout the northeastern United States, salmon experienced a sharp decline in overall population due to the destruction of habitats and pollution in the streams where the salmon bred. While they still have not returned to all previously known salmon rivers, remarkable headway has been made by the release of young salmon into reclaimed rivers and streams through hatchery programs. It is too soon to tell if this beautiful fish can reestablish itself with viable breeding populations, since it takes four or more years for their return from the sea.
Eels are scavengers and eat virtually anything dead or alive.
For many years scientists were baffled as to their breeding habits. It was known that females lived for the most part in freshwater and males in brackish or estuarine waters. It was surmised that they bred in the ocean but little more was known. They then traced the eels' spawning grounds by finding smaller and smaller larvae until they reached an area called the Sargasso Sea. The eel is termed catadromous because of its journey from freshwater to the depths of the ocean to spawn.