Known primarily as solitary animals, new research is showing that sharks likely have a much more complex social structure than previously thought. The findings reveal social networks more typically seen in mammals than in fish.
Researchers followed over 300 sand tiger sharks for a year using tracking devices, recording all shark to shark interactions. It was the first study to record interactions for almost a full year in wild sharks. The findings were presented today (February 22) at the 2016 Ocean Sciences Meeting sponsored by the American Geophysical Union.
“Higher-order decision making processes are often associated with mammals, or species that we think of as really smart like dolphins, elephants, or chimpanzees,” said Danielle Haulsee at the University of Delaware in Lewes. “Our research shows that it is important for the scientific community to not rule out these types of behaviors in non-mammalian species, as behavior can often give us insight on how species interact with their ecosystems and how resources that humans depend on are distributed around the world.”
Scientists isolated two individual sharks and found that they each encountered over 200 sand tiger sharks throughout the year, as well as many other encounters with different species of sharks. Results showed that groups of sharks would stay together during certain times of the year and fall apart at other times. The sharks seem to be pretty selective and loyal as they would make a point to re-encounter the same sharks throughout the year.
One surprise showed a lack of encounters in the late winter, early spring period. Scientists suggest that the sharks may be busy performing a kind of social cost-benefit analysis based on mating priorities and searching for food.
“If you’re living with a group, there could be some kind of protection or information sharing that comes with being in that group,” Haulsee said. “But if there’s a lot of competition for food resources or mating resources, then it’s not beneficial anymore to be in a group, and you might swim away from your group and go off on your own.”
The study encompasses the largest and longest ever tracking of sharks, allowing scientists to understand where the sharks are located all year-round.
Haulsee says their results have implications for assisting in conservation efforts: “If we know where and when the population is grouped, we can focus on limiting human-induced disturbances in those times and places. For example, if we know there are certain times and places where breeding females, or even more importantly the pregnant females, are aggregated together, we can devote resources into those areas to protect those sharks.”