Social Swimmers

If you go walking with a friend, the odds are that your preferred walking speeds won’t be the same. So the person who usually walks faster probably will slow down a little. That person might not hit their preferred heart rate, but being sociable is more important.

And the same thing might apply to some fish. They appear to adjust their swimming speed to stick with others of their kind. That might not be their optimal speed, but it’s one that provides other benefits.

Fish that migrate over great distances maintain a “Goldilocks” pace as they go. It’s fast enough to get them where they want to go in a reasonable time. But it’s not so fast that they’re worn out by the swim, or can’t mount a quick burst if they face danger.

But fish that hang out close to shore and don’t migrate tend to vary their speed a lot, depending on what they’re doing. They might need to change pace to avoid obstacles on the sea floor, to catch prey, or to woo potential mates. And they might just want to hang around with others—a strategy that might make life safer or easier.

Researchers recently studied a type of surfperch caught off the coast of Washington. They studied the swimming habits of the fish in the lab. They put pairs of fish in a contraption that’s the marine equivalent of a treadmill. And they found that if one member of a pair was faster than the other, it didn’t just pull away. Instead, it slowed down to stay with its companion—just keeping things sociable.