Salmon

Almost everyone knows salmon swim upstream to spawn. Almost nobody knows they use the Earth's magnetic field like a GPS to navigate open ocean back to the exact stream where they hatched — sometimes to within meters. Or that when they die after spawning, their bodies feed a forest: nitrogen from their ocean-fed carcasses moves through bears, eagles, insects, and soil into the trees lining the rivers where they were born.

Facts you didn't know

• 1

  Salmon imprint on the specific chemical signature of the stream they hatched in as juveniles, then use this olfactory memory years later to navigate back to the same tributary — sometimes to within meters of the exact gravel bed where they emerged.

• 2

  Before that final leg, salmon navigate open ocean using the Earth's magnetic field — detecting both field intensity and inclination angle to triangulate their position across thousands of kilometers of featureless water, matching navigational accuracy that took humans centuries of technology to achieve.

• 3

  A single salmon carcass provides more nitrogen to a streamside forest than a year of normal decomposition in the same area. Bears, eagles, and wolves drag salmon up to 150 meters into forest, and the resulting nutrient pulse is detectable in tree ring records — wider rings in years of strong salmon runs.

• 4

  Sockeye salmon turn crimson and grow humped backs when returning to spawn — hormonal changes that redirect energy from feeding to reproduction and territory defense. The fish arriving at the spawning ground is physiologically almost a different animal from the one that left the ocean.

• 5

  Salmon that fail to reach their spawning grounds still release nutrients when they die en route. Evolution has essentially ensured the forest gets fed regardless of whether the individual succeeds.