Page 178 - The Miracle of Migration in Animals

THE MIRACLE OF MIGRATION IN ANIMALS

An Example of the Salmon’s Incredible

Journey

In reality, every river on Earth has its own unique chemical com-
position. The differences between these characteristic smells are so
small that almost no animal could perceive them.
Except the salmon...
An incident at the Prairie Creek Fish Hatchery in North
California exposed an incredible migration adventure. 49
On 2 nd December, 1964, a salmon judged by its size to be two
years old was found in one of the rearing tanks among the hundreds
of young fish. Its back fin bore the special metal clip of the hatchery,
showing that this fish was one of those reared two years before, that
had been released into the ocean. But how had it managed to return
and get into one of the enclosed tanks of the fish hatchery?
The metal grill covering the entrance to the canal used to drain
excess water from the tank was found to be broken. To return to its
birthplace, could the salmon have gone into one of the hatchery’s
drainage canals and broken the cover to reach the tank?
There was no other explanation. But considering the route the
fish had to take to get from the ocean, it would seem impossible.
To return to this tank where it was reared, the salmon would
have to start its journey from where the Redwood Creek flows into
the ocean. Then, after swimming upstream for five kilometers (three
miles), the fish would have come to the first fork in the stream. After
deciding which to take, it would have swum north—to encounter a
more difficult decision, because this next fork would have presented
two very similar signals. The hatchery where the salmon was reared
lay right between the two branches of the river. The salmon would
have thought first of taking the right fork, because the hatchery’s

water flowed down from the right.

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