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There's Something Very Fishy About These Trees ... | Deep Look

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Channel: Deep Look
Categories: Biology   |   Environmental   |   Science  
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Salmon make a perilous voyage upstream past hungry eagles and bears to mate in forest creeks. When the salmon die, a new journey begins – with maggots.

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DEEP LOOK is a ultra-HD (4K) short video series created by KQED San Francisco and presented by PBS Digital Studios. See the unseen at the very edge of our visible world. Get a new perspective on our place in the universe. Explore big scientific mysteries by going incredibly small.


For salmon lovers in California, October is “the peak of the return” when hundreds of thousands of Chinook salmon leave the open ocean and swim back to their ancestral streams to spawn and die. All along the Pacific coast, starting in the early summer and stretching as late as December, salmon wait offshore for the right timing to complete their journey inland.

In Alaska, the season starts in late June, when salmon head to streams in lush coastal forests. Although this annual migration is welcomed by fishermen who catch the salmon offshore, scientists are finding a much broader and holistic function of the spawning salmon: feeding the forest.

Millions of salmon make this migratory journey -- called running -- every year, and their silvery bodies all but obscure the rivers they pass through. This throng of salmon flesh coming into Alaska’s forests is a mass movement of nutrients from the salt waters of the ocean to the forest floor. Decomposing salmon on the sides of streams not only fertilize the soil beneath them, they also provide the base of a complex food web that depends upon them.

--- Why Do Salmon Swim Upstream?
Salmon run up freshwater streams and rivers to mate. A female salmon will dig a depression in the gravel with her tails and then deposit her eggs in the hole. Male salmon swim alongside the female and release a cloud of sperm at the same. The eggs are fertilized in the running water as the female buries them under a layer of gravel.

When the eggs hatch, they spend the first part of their lives hunting and growing in their home stream before heading out to sea to spend their adulthood.

--- Why Do Salmon Die After Mating?
Salmon typically mate once and then die, though some may return to the sea and come back to mate the subsequent year. Salmon put all of their energy into mating instead of maintaining the salmon’s body for the future. This is a type of mating strategy where adults die after a single mating episode is called semelparity.

---+ Read the entire article on KQED Science:

---+ For more information:
Bob Armstrong’s Nature Alaska

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