It’s safe to assume that most people probably don’t think of sharks as being the friendliest of animals. Those black eyes and rows of teeth don’t exactly conjure up words like “friendly” or “buddy.” Sure, some sharks do swim in schools and participate in feeding frenzies, but is it possible that while they’re ripping away at chunks of flesh that they could be saying to one another “Hey old pal, care for another bite of chum?”
Well, according to a study from Florida International University in Miami, sharks do indeed have friends. A four-year study looked at grey reef sharks at Palmyra Atoll, one of the Northern Line Islands south of Hawaii in the Pacific Ocean, and found that the sharks would visit with certain other sharks in the area over long periods of time.
In order to study the grey reef sharks behavior and determine whether or not they truly did have “friends,” scientist Yannis Papastamatiou and other researchers tagged 40 of the sharks with acoustic transmitters. The transmitters emitted a high-frequency sound and were outfitted with batteries to last at least four years. The team then set up a network of 65 receivers to record the identity of a tagged shark that swam within 300 meters of one of those receivers.
What they discovered was particularly surprising — at least in terms of shark social structure.
Not only did the transmitters and receivers yield data that showed grey reef sharks have stable social groups, but that certain sharks would hang out with other individual sharks year after year.
“We don’t think of sharks as social animals, but they do have social groups,” Papastamatiou said. “They purposely associate with the same individuals.” The researchers don’t know exactly how the sharks recognize certain other sharks, whether it’s smell, sight, or something else, but they most certainly can.
Grey reef sharks are most active at night when they feed and during the day congregate in groups of 20 or more sharks. Papastamatiou and his team aren’t sure if the same individual shark pairs hunt together at night, or if it’s more of a group effort. It was previously believed that grey reef sharks hunted mostly around reefs (hence the name) but researchers discovered that a fair amount of their hunting took place in open waters away from the reef.
Perhaps saying that sharks have “friends” might be a bit of an overstatement, according to Papastamatiou. (Who needs a friend when you’re the top predator in the ocean?) “They are not friends in the sense of having any emotional bond with each other,” he says. Perhaps “associate” is a more fitting description than “friend” to describe the grey reef sharks’ relationships with one another.
After all, friends tend to help each other out and so far, the team hasn’t recorded any direct examples of the sharks lending each other a helping hand — or fin, to be more accurate.
Photos via Flickr, BBC Earth