Dear Norma,

While a lot of fish swim from one region to another to find food or have babies, different fish species migrate in different ways.

That’s what I found out from friend Steve Katz, a professor at Washington State University who knows a lot about our planet’s natural resources and has researched fish such as steelhead trout, tuna and seven-gilled sharks in the Pacific Northwest.

He said that steelhead trout often navigate through the water with help from a sense of smell. Steelhead trout use their nostrils to pick up on chemicals from rocks that have dissolved in the water. The differences in the scents of the water help them know which river or stream to follow.

This is a helpful tool, especially as steelhead trout can swim for long distances over the course of a few years—in some cases, over 1,300 miles upstream after they swim through the ocean for more than 3,700 miles.

Katz reminded me that not all fish migrate. For instance, some of the steelhead trout males will stay behind in the streams when the females and other males head for the ocean. There is some risk in traveling long distances, so it can pay off for some fish to stay home and wait for the females to return.

If you think a few thousand miles is a long way to swim, wait until you learn about tuna. Albacore tuna cross the Pacific Ocean twice a year cruising at speeds of 5-10 miles per hour. In a lifetime, that might add about 20 to 25 round trips. When it comes to migration, these fish are marathoners.

“It’s spectacular,” Katz said. “Tuna are elite swimmers because they’ve got this extra red muscle and machinery that helps them swim at a steady, fast pace.”

A fish that moves much slower is the seven-gilled shark. These fish live where the saltwater meets the freshwater, or often where rivers meet the ocean, which we call an estuary. But when it starts raining a lot in the winter, there isn’t enough saltwater in the estuary anymore. They have to head out into the ocean.

The sharks travel up and down the coast for anywhere from 100 to 1,000 miles while they wait for the estuary to become saltier, and then they make their journey home for the summer.

Katz said that some research has also explored how fish might use Earth’s magnetic field—which extends from our planet’s interior out into space— or the angle of the sun to know which direction they should be going. But the truth is, scientists are still learning a lot about exactly how fish navigate the waters on their migration.

Perhaps you can find a species of fish that lives in your state and learn more about its migration journey. The more species you learn about the more you’ll realize just how many migration stories there are to discover.

Dr. Universe