Nature · Level 3 · 194 words

Salmon Find the Way Home

Original passage © Studio AM, written for Fluency.

A young salmon leaves a small stream, swims to the sea, and spends years there. Then, as an adult, it comes back. Not to the coast in general, but to the same stream where it hatched.

It solves the problem in two steps. Far out at sea, the fish appears to read the Earth's magnetic field, which differs slightly from place to place and works like a rough map. That map is good enough to bring the salmon near the right stretch of coast, but not good enough to pick one creek out of a hundred.

Close to shore, the salmon switches to smell. As a young fish it learned the particular odour of its home water: the soil, the plants, the rock the stream ran over. Now it tests the water at each junction and turns toward the smell it remembers.

The journey ends in exhaustion. Pacific salmon spawn once and then die, and their bodies stay in the stream. Bears drag some of them into the trees. Chemical tests can find, in the wood of forests beside such streams, nitrogen that came from the open ocean and was carried inland inside fish.

Comprehension questions

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4 questions
1. What is the passage mainly about?

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A. Salmon use two different methods, one at sea and one near the coast, to return to the exact stream where they hatched.
The middle paragraphs are organised as step one and step two of a single navigation problem. The bears and the nitrogen come after the journey and are not the subject.

2. What does the salmon use to choose the right creek once it is close to shore?

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B. the smell of its home water
Paragraph three says the salmon switches to smell and turns toward the odour it learned as a young fish.

3. Why is the magnetic map not enough on its own?

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C. It brings the fish to the right region but cannot separate one creek from its neighbours.
The text says the map is good enough for the right stretch of coast but not for picking one creek out of a hundred. That gap is exactly what smell fills.

4. In this passage, "junction" means

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A. a place where waters meet and the fish must choose a way
The salmon tests the water at each junction and then turns. A choice of direction is only needed where two waters meet.

Source: Written for Fluency. Original passage © Studio AM, written for Fluency.