Sharks not as lonely as previously thought

Far from being solitary animals, as they have been historically seen, sharks can actually form complex social network that are typically seen in mammals but rarely observed in fish, new research has found.

"Higher-order decision-making processes are often associated with mammals, or species that we think of as really smart - dolphins, elephants, or chimpanzees," said one of the researchers, Danielle Haulsee from University of Delaware in Lewes, US.

"Our research shows that it is important for the scientific community to not rule out these types of behaviours in non-mammalian species, as behaviour can often give us insight on how species interact with their ecosystems and how resources that humans depend on are distributed around the world," Haulsee noted.

The findings were presented at the 2016 Ocean Sciences Meeting in New Orleans, Louisiana, US.

The researchers used acoustic tags to track the movements of over 300 individual Sand Tiger sharks and record shark-shark interactions over the course of a year.

Sand Tiger sharks, top predators that live in coastal waters off the eastern US, have experienced drastic declines in numbers over the past several decades.

Initial data from two individual sharks showed they encountered nearly 200 other Sand Tigers throughout the year, as well as several individuals from other shark species.

These sharks exhibited fission-fusion social behaviour, meaning that the number of sharks in a group and the individuals that are part of the group change by location and time of year.

The researchers found that groups of 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.

One surprise was a sudden lack of encounters with other Sand Tigers in the late winter and early spring, Haulsee said.

This could be related to other aspects of the sharks' lives, such as mating and searching for food, which suggests that they could be performing a kind of social cost-benefit analysis, Haulsee noted.