The annual migration of adult salmon from the ocean back to the freshwater rivers and streams where they hatched, undertaken to spawn the next generation, often against powerful currents and up steep waterfalls, over distances that can exceed a thousand miles for some Pacific salmon populations. Most Pacific salmon die within days or weeks of spawning, and their decomposing bodies deliver a substantial pulse of ocean-derived nutrients into freshwater and forest ecosystems.
Facts
PeriodicityMost salmon species migrate upstream to spawn during the autumn, from September through November. 1 ScaleCentral Idaho's Chinook and sockeye salmon must travel 900 miles (1,400 km) upriver and climb nearly 7,000 feet (2,100 m) in elevation before they are ready to spawn. 1 First DescribedThe mechanism salmon use to find their way back to their home river with precision, recognizing its characteristic smell, was scientifically identified by researcher Arthur Hasler and his students in 1978. 1 Identification
Distinguishing AppearanceReturning salmon lose the silvery blue coloring of their ocean phase and darken, sometimes dramatically, while males develop canine-like teeth and a pronounced hooked jaw called a kype. 1 Sources
1. Salmon run - Wikipedia
Background section
Most salmon species migrate during the autumn (September through November).
Obstacles section
Chinook and sockeye salmon from central Idaho must travel 900 miles (1,400 km) and climb nearly 7,000 feet (2,100 m) before they are ready to spawn.
Return from the ocean section, sentence on Hasler's 1978 homing study
In 1978, Hasler and his students found that the way salmon locate their home rivers with such precision was because they could recognise its characteristic smell.
Return from the ocean section, sentence on color change and kype development
All salmon lose the silvery blue they had as ocean fish, and their colour darkens, sometimes with a radical change in hue.
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