Bull sharks keep friendships 'fin' the family

It's fins not phones in the bull shark family group chat, as the animals prefer to spend time with their relatives underwater.

New research in Fiji suggests some adult bull sharks are slightly more likely to spend time with family members than with unrelated sharks.

Researchers – from the University of Exeter, Fiji Shark Lab and Lancaster University used genetic data, which can show family links, and six years of underwater observations.

Most of the sharks in the study were not close family members. Even so, the researchers found a small but interesting pattern: related sharks were a little more likely to hang out together.

Researchers came up with the phrase 'kinfluence' to describe the observed behaviour. 'Kin' is another word for family.

The scientists watched for shark "social moves", including parallel swimming, "lead-follow" swimming and "joining", when one shark joins another and swims in time with it.

Lead author Natasha D. Marosi from the University of Exeter, and Fiji Shark Lab founder, said: "Large sharks are often seen as solitary, but our previous research showed that bull sharks actively choose their social partners." She added:

"To discover that some of these large, apex predators choose to socialise with their relatives is truly exciting, it's something never found before in an adult population of sharks."

Marosi said young bull sharks may spend their early lives near full siblings, half-siblings and cousins in rivers and estuaries and are then able to recognise them again when they get older.

Dr Andrew Griffiths, also from the University of Exeter, said the results show sharks in "a completely new light".

"The results are fascinating, especially as sharks are still widely perceived as fearsome and solitary animals."