There are less than twenty different species of salmon. The Atlantic salmon, Salmo salar, depicted on the top, is iteroparity, a term describing a salmon able to survive through more than one breeding season. The Atlantic salmon goes to sea and returns to the stream of its birth, usually for two cycles. The other species, such as the silver salmon, Oncorhynchus kisutch, depicted on the bottom, are Pacific coast salmon. They go out to sea and return many years later to spawn only once. The remarkable ability in being able to find their back to the stream of their birth and to manage this feat against overwhelming odds is difficult to fully comprehend and appreciate. Through various tests, scientist have concluded salmon have an acute sense of smell and are able to smell their way back home. This homing behavior is known as olfactory memory.
