Traveling Sharks

For much of the summer, sand tiger sharks gather in and around Delaware Bay. But when summer’s over, it’s like an extended family at the end of a long reunion — everybody heads their own way.

Tiger sharks are best known for being big, fast, and aggressive — and for their ability to eat just about anything: fish, sea turtles, birds, and even garbage — everything from plastic bottles to metal license plates. They also get around — they can migrate many hundreds of miles. The sand tigers from Delaware Bay, for example, have been spotted as far away as Florida. But some ongoing research shows that they don’t go south as a group.

Biologists have been implanting tracking devices in the Delaware Bay sharks for years. And in 2012, they implanted more-sophisticated devices in 20 sharks. These devices show not only where the sharks have been, but whether they’ve been around any other sharks or other creatures with their own trackers.

The scientists recaptured two of the sharks and retrieved the data on their devices. That allowed them to see how the sharks dispersed when they left the bay.

The trackers showed that the sharks headed out in small groups, usually led by males. Several of the groups came together off the coast of North Carolina, then they split up again. By the time they reached sunny Florida, the sharks were pretty much alone. When they returned northward, though, their social groups came back together — an extended family ready for a summer reunion.