A salmon begins its life in a shallow, swift-moving stream. After feeding for a
few weeks, it begins a long journey. It follows the current down to another
stream, perhaps to another, then out to a river. It eventually swims out into
the ocean, where it roams a vast area, sometimes traveling thousands of miles
from its birthplace.
If that weren't remarkable enough, the salmon will someday return home, back to
the river mouth from which it emerged, back up the same waterways it descended,
back to the very stream where its life began.
It's an amazing journey—one that has caused more than one biologist to
scratch her head. But experiments have shown that the fish actually smell their
way to their nesting sites. Odors from the stream—perhaps minerals and
organic substances washing in from the surrounding land—become more intense
as a fish swims upstream and help it decide which route to take whenever it
encounters a fork.
In this activity you are a salmon trying to find its way home. Since your human
sense of smell is not nearly as acute as your fishy relative's (and since the
technology that spits out odiferous molecules from a computer peripheral has
yet to be developed), you'll have to rely on the "smells like home" meter
within the activity to help guide you along.