Many sharks like the company of family and friends, with researchers only just beginning to understand the complex social lives of these ocean predators.
Shark schools, hierarchies, alliances and other shark-to-shark connections offer benefits, helping to explain why many toothy marine dwellers not only put up with each other, but also often seem to enjoy doing so.
These whitetip reef sharks were photographed hanging out together in Guam. Shark expert Greg Stone, chief scientist at Conservation International, told Discovery News, "These sharks live on busy reefs where there are a lot of fish. They hunt in groups at night and also rest in caves with other whitetips during the day. They have also been observed hunting along with other species of sharks on the reef."
Bonnethead female sharks go out to lunch together, gathering in certain South Carolina's estuaries to feast on blue crabs. William Driggers III of the National Marine Fisheries Service and colleagues recently noted the behavior in a paper accepted for publication in the Journal of Experimental Marine Biology and Ecology.
The researchers suspect "that feeding area location is socially transmitted among bonnetheads," so the sharks generously share the good news about good eats with select others.
When the Galapagos shark was first described in 1905, Robert Evans Snodgrass and Edmund Heller observed many of the sharks swimming together in the water. Stone can vouch that these sharks often stick together and show a playful curiosity.
"I have been in amongst large schools around Midway Islands in the Central Pacific," Stone said. "They are a relatively harmless shark to humans, but I do remember they gathered around me and nipped at my flippers like puppy dogs."
"Blacktips are one of the most common sharks found on reefs," Stone said, adding that "blacktips can be found in large social groups. I've seen hundreds of these around the Phoenix Islands (in the Central Pacific); the small shark pups live in the lagoons until they are large enough to swim in the outer reefs."
"Social behavior has been observed frequently in this species of reef shark," Stone said. "Pregnant females have been observed schooling together in shallow water. Some schools of grey reef sharks can reach 30 individuals."
"Grey reef sharks are very territorial," he added. "I have dived many times with grey reefs and you have to keep an eye on them because if you wander into their territory and they are in a protective mood, they will menace you with special posture (they hump their backs and extend their pectoral flippers), which means leave or else. As long as you pay attention to this and depart, you are fine."
"Scalloped hammerhead sharks form huge schools, numbering in the hundreds, during the day when they are not hunting," Stone said. "These schools swim around seamounts, submerged mountains that are a habitat for a diverse amount of sea life."
Lemon sharks, which live in mangroves, river mouths and on reefs, never seem to be alone. They form bonds with fellow lemon sharks and are also often accompanied by remoras (aka suckerfish), as seen in this photo. Remoras help to keep sharks clean by eating off parasites, dead shark skin and more.
As for lemon sharks, Stone said, "It is a shark species that can live well in captivity, so it is one people have had the chance to study for over five decades. Young lemon sharks have been observed to have small groups of other sharks that they prefer to be around."
He added, "I have waded into mangroves and held young pups in my hand in the Bahamas. This is a lovely and very benign shark."
"This species is popular in aquariums because it lives in shallow water and it swims with its mouth open presenting its rows of sharp teeth," Stone said. "They can hunt cooperatively, with individuals swimming around a school of fish to concentrate it, allowing others to swim through the bait ball to feed."
"At night, this typically docile species of shark hunts for shrimp, squid and lobster," Stone said. "During the day, groups of up to 40 of them congregate together on the bottom to rest."
"This shark, which can grow up to three feet long, forms single-sex schools which can reach over a hundred individuals," Stone said. "Sold for its meat, oils and fins, their population has declined drastically since the 1960s."
He added, "Over the last 50 years, science has come a long way to understand sharks. We know that they are incredibly important to keeping the marine ecosystem in balance and therefore play an integral role in the productivity of fisheries on which humans depend."
"Typically, most sharks are thought of as solitary creatures, however, there are plenty of sharks out there that are social creatures."