Most of us are probably familiar with the image of salmon jumping upstream or over obstacles in the water. But why is it so common to see them leaping out of still water too?

Maybe they're just showing off. Or, they might be trying to shake off sea lice.

Scientists noticed that young sockeye salmon jump out of the water and skim its surface with their tails an average of nine times a day, and it’s clear they’re not just leaping over obstacles. Researchers had a hunch the salmon were trying to get rid of sea lice, since it’s known that fish with sea lice jump out of the water fourteen times more often than fish that are sea lice-free.

A sea louse is a parasite about the size of a pea that feeds on mucus, blood, and skin, so it makes sense why salmon want to get rid of them. But does jumping actually do the trick?

That’s what scientists wanted to find out. They caught salmon infested with sea lice and divided them into two groups. They put one into an ocean pen where they could leap out of the water, and another into a pen with netting covering the water’s surface. After three days, the salmon that couldn’t jump out of the water had twenty-eight percent more sea lice than the ones that could.

So the salmon figured out something that works, eventually. It takes the fish an average of fifty-six jumps to dislodge a single sea louse.

Not the best stats. They should really work on their technique.

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Source

• Science Magazine - Why are these salmon jumping?