Salmon is one of the few foodstuffs still caught in the wild for general consumption in the United States. As such, their reproduction is of great interest and importance to the fishermen that rely on them. Learning how and why salmon spawn is beneficial to fishermen and environmentalists alike.
Benefits of Upstream Spawning
Adult salmon live their lives in the depths of the Pacific Ocean. While they are eggs and babies, however, they rely on the shallows of the streams and rivers to provide safety and food. Salmon swim upstream to return to the place they remember being hatched for refuge. Salmon successfully spawn, hatch and live in the shallows of riverbeds and streams because of the suitable environment. The rocky stream floor is close to the surface of the water. There, the eggs are able to hatch without floating off or being washed away by heavy tide. The stream provides rich food sources once the eggs have become baby fish. The shoals also prevent many predators from being able to access the helpless little fish.
Adaptions to Spawning
Because salmon swim upstream to spawn, the number of males available is deeply condensed in comparison to the open ocean. Male salmon grow hooked snouts, brighten in color and undergo other physiological changed to make themselves more sexually desirable to mates. Female salmon turn slightly to one side and use their tail to create a depression to make a nest in. After the nest is finished, the females do a mating ritual to draw males to compete to fertilize the freshly laid eggs.
When eggs are laid in their gravel nests, they are red, orange or pink spheres. They stay in their translucent shells for up to three months. After hatching, the babies, now called alevin, will stay in the safety of the nest, consuming the rest of the egg yolk for another month. At the end of their time in the nest, the tiny salmon are fry, leaving the nest to make their way downstream. Several months of being a small fry yields a young fish called a parr, who will still live in the streams and rivers for up to three more years before ever heading to the ocean. Juvenile salmon, called smolt, now begin to swim in schools. They slowly adjust to salt water as they edge toward the ocean. Once salmon become adults, the fish spend up to four years swimming freely in the ocean. The fish develop specific and unique species markings. After their lively adulthood, salmon are ready to spawn.
Salmon remember the smell of the stream they were born in. After reaching their birth rivers and streams, the adult salmon re-adapt to the fresh water and begin their upstream journey to their natal stream. Usually accustomed to drinking saltwater and making use of their salt glands, once returning to freshwater salmon tend to bloat, forcing them to create large amounts of urine. Their stomachs become emaciated and they stop feeding, living only on the stores of fat. This emptiness leaves more room for sperm or eggs. Male salmon arrive first and start to stake out territories. When the female salmon arrive the spawning process begins. Female salmon release between two and ten thousand pea-sized orange eggs. Male salmon release white milt containing millions of sperm. The adult fish die within a few weeks of spawning.
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