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Sharks are Social Like Dolphins, Chimpanzees: Study Reveals

Sand Tiger sharks, found in the coastal ocean along the Eastern US Coast along the Delaware Bay and surrounding coastal waters are historically seen as solitary animals but new research has shown that the sharks may have a more complex social structure than previously thought.

Since 2007, researchers in oceanography at the University of Delaware in Lewes have implanted more than 300 VEMCO acoustic transmitters in Sand Tigers, which have been detected from Cape Canaveral, Florida to Long Island, New York by collaborators in the Atlantic Cooperative Telemetry (ACT) Network.

During the summer of 2012, 20 Sand Tigers were implanted with VEMCO Mobile Transceivers (VMTs), and two of the 20 sharks have been recaptured, and their VMTs recovered. These VMTs recorded detections of 350 individuals, from 8 different species.

Researchers found that the sharks exhibited more complex social networks that are typically seen in mammals but rarely observed in fish. "Higher-order decision-making processes are often associated with mammals, or species that we think of as really smart – dolphins, elephants, or chimpanzees," said Danielle Haulsee, a PhD scholar at the University of Delaware in Lewes.

"We analyzed their intra- and interspecific social network, which allowed us to reconstruct the approximate locations of Sand Tigers throughout the year. Changes in the interspecific population dynamics throughout the year revealed evidence of fission-fusion social behavior, which is common in mammals, but rarely documented in non-mammalian species," he said.

In addition, understanding how the aggregations of this species changes (in terms of sex and size class segregation) on spatiotemporal scales is critical for effective protection of the species and will be useful as managers develop conservation plans along the East Coast.

The data from two individual sharks showed that they encountered nearly 200 other sand tigers in a year and several other individuals from other shark species. Some Sand Tigers stay together for certain times of the year and fall apart during other times. They also found that Sand Tigers re-encounter the same sharks throughout the year, except during the winter perhaps due to mating and searching for food.

The paper will be presented at the 2016 Ocean Sciences Meeting co-sponsored by the Association for the Sciences of Limnology and Oceanography, The Oceanography Society and the American Geophysical Union.

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