The upriver salmon run is one of nature’s great migrations. Each year mature salmon make the long journey back to their natal river to reproduce, just once. For the five species of Pacific salmon (Chinook, chum, coho, pink, and sockeye), this arduous journey is a race against the clock that ends in a fleeting romance and ultimately death.
The answer to why they die, it turns out, hinges on a problem every animal on Earth has had to solve.
“Every kind of organism has evolved to solve the problem of balancing how much energy to put into surviving to first reproduction and how much energy to put into surviving to reproduce repeatedly,” said Steve Lindley, the director of NOAA’s Fisheries Ecology Division.
“Salmon are one of the extreme cases where they put everything into reproducing just once, and then getting old and dying almost immediately thereafter (a common strategy among insects but much less so for vertebrates).”