Where Do Salmon Go to Breed?
Atlantic salmon, called the “greatest game fish in the world” by sportsmen, spawn in the fresh water streams of Europe, from Portugal to northern Russia, and in the streams of the eastern seaboard of North America, from Maine up to northern Canada.
They are found also in the streams of Greenland and Iceland. Pacific salmon, of which there are several kinds, spawn in the streams of southern Alaska, British Columbia and the states of Washington and Oregon on the Pacific coast. There is also one kind which breeds in the streams of Russia’s east coast.
The females spawn their thousands of eggs and the males fertilize them. Once the Pacific female salmon have spawned they die. The eggs hatch in about 19 weeks. The tiny salmon called an “alevin” hides in the gravelly bed of the stream, living at first on a large yolk-sac under its body.
When about a year old it is called “parr” and looks like a young trout. Six months later when it has a more salmon look it is called a “smolt”. On reaching the sea it becomes a “grilse” until it reaches maturity.
The instinct of the salmon to head for the sea after a couple of years in fresh water is one of the great mysteries of nature. So too is its instinct, after ranging the Atlantic and Pacific Oceans and traveling up to 4,000 miles, to return to spawn in the stream where its own life began.
It is thought that, when they are in the ocean, they use magnetoception to locate the general position of their natal river, and once close to the river, that they use their sense of smell to home in on the river entrance and even their natal spawning ground.
In northwest America, salmon is a keystone species, which means the impact they have on other life is greater than would be expected in relation to their biomass. The death of the salmon has important consequences, since it means significant nutrients in their carcasses, rich in nitrogen, sulfur, carbon and phosphorus, are transferred from the ocean to terrestrial wildlife such as bears and riparian woodlands adjacent to the rivers.
This has knock-on effects not only for the next generation of salmon, but to every species living in the riparian zones the salmon reach. The nutrients can also be washed downstream into estuaries where they accumulate and provide further support for estuarine breeding birds.
Most salmon are anadromous, a term which comes from the Greek anadromos, meaning “running upward”. Anadromous fish grow up mostly in the saltwater in oceans. When they have matured they migrate or “run up” freshwater rivers to spawn in what is called the salmon run.
Anadromous salmon are Northern Hemisphere fish that spend their ocean phase in either the Atlantic Ocean or the Pacific Ocean. They do not thrive in warm water. There is only one species of salmon found in the Atlantic, commonly called the Atlantic salmon. These salmon run up rivers on both sides of the ocean. Seven different species of salmon inhabit the Pacific, and these are collectively referred to as Pacific salmon.
Five of these species run up rivers on both sides of the Pacific, but two species are found only on the Asian side. In the early 19th century, Chinook salmon were successfully established in the Southern Hemisphere, far from their native range, in New Zealand rivers. Attempts to establish anadromous salmon elsewhere have not succeeded.