Page 66 - Engineering in Nature

Engineering in Nature

• Problems Salmon Have to Overcome
On its return route, the salmon must first find the mouth of the
river where it was hatched. Salmon never make a mistake in this re-
gard. On their first attempt, they're easily able to find the mouth of
the river that opens into the ocean.

Entering the river, a salmon begins to swim with great determina-
tion against the current.
In order to reach its objective, the salmon struggles against the riv-
er's powerful current. It overcomes the waterfalls and similar obsta-
cles rising up before it by leaping sometimes as high as 3 meters (10
feet) in the air. Sometimes it passes through water so shallow that its
upper fin is exposed to the air. In these shallow waters, it faces the
danger of predators such as
eagles, hawks and bears that
wait for it.
In order to fully under-
stand the perfection of the
salmon's journey, consider
what it must keep in mind to
reach its destination:
First, to determine its
route, it needs to take a num-
ber of important decisions.

The fish are hatched a consid-
erable distance inland, in any
of the river's number of vari-
ous branches. Thus the
salmon must correctly select
every fork in the river. Yet

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