But it's survival depends on the deep ocean, hundreds of miles away.

What could possibly bind the two together?

These guys - chum salmon.

As adults, they patrol the Pacific, gorging themselves and growing fat.

But after a few years,

The streams where they were born call to them.

The salmon are hypnotized by smell of the freshwater, flowing from melting snow on the

mountains above.

By the thousands, they mob together and charge upstream.

Eagles feast on the stampede of flesh.

The salmon are relentless.

They don’t even eat.

They just swim.

They’re reaching the end of their lives,

But they have one last thing to do before they die

Females dig little nests in the gravel with their tails.

Then they lay their eggs, which the males fertilize.... thoroughly.

Then she covers them up.

For most of these salmon, there’s no hope of making it back to sea.

It’s the end for them.

But wait, this story isn’t done.

One way or another, the salmon carcasses make their way up onto the river banks,

into the forest.

But bears are sloppy eaters, they take their favorite bits and leave rest to decay.

That’s a score for these blow flies.

They taste the flesh to make sure it’s to their liking - but not because they’re going

to eat it.

Their kids will call this carcass home.

The fly eggs hatch into maggots that set to work devouring the salmon.

Rotting flesh is their thing.

When they’ve had their fill, the maggots squirm off and bury themselves underground

until they’re ready to emerge as adult flies.

They scatter off to live their lives in the forest.

When they die or get eaten, the nutrients from the salmon

get spread throughout the ecosystem.

Things like nitrogen, that plants need to grow.

So the river is like an artery - bringing an influx of vital nutrients direct from the

deep ocean.

In these coastal forests, up to 80% of the nitrogen in the plants can be traced back

to the salmon

And the blow flies have one more important job - pollinating fields of flowers.

It’s all thanks to these intrepid fish - who nourish an entire ecosystem.

Year after year.

These little guys are baby coho salmon, ready to take their first big journey out into the

ocean.

Make sure you’re in on our journey, and hit that subscribe button.

We’ll let you know about new episodes, twice a month.

And check out this episode of It’s OK to Be Smart about why beavers are master builders.

It’s from the same trip to Juneau, Alaska where we filmed this episode.

See you next time.