White Sharks Choose Who They Hang With, New Study Reveals

White sharks (Carcharodon carcharias) are top marine predators that are typically solitary but can also form seasonal aggregations around seal colonies to feed. Using a combination of photo-identification and network analysis, a team of researchers investigated the co-occurrence patterns of the marine predators. The study showed, for the first time, that many of the white sharks hang out in groups which persist for years.

The white shark (Carcharodon carcharias). Image credit: Hermanus Backpackers / CC BY 2.0.

At the Neptune Islands in the Great Australian Bight, large numbers of white sharks can be sighted throughout the year, including during periods of low seal abundance.

Dr. Charlie Huveneers, a researcher at Flinders University and lead author of the study, and his colleagues from Australia and France spent four and half years taking multiple photographs of 282 sharks (183 males, 97 females, 2 unknown).

The scientists were able to identify individual sharks and, to their surprise, found that many were seen in proximity to specific others far more often than chance would determine.

Tendency to co-occur varied across months with males co-occurring with more individuals than females.

Sex-dependent patterns of visitation at the Neptune Islands and resulting competition likely drive the observed community structure and temporal variability in co-occurrences.

“Rather than just being around randomly, the sharks formed four distinct communities, which showed that some sharks were more likely to use the site simultaneously than expected by chance,” said study co-author Dr. Stephan Leu, a behavioral ecologist at Macquarie University.

“The numbers varied across time, and we suggest that sex-dependent patterns of visitation at the Neptune Islands drive the observed community structure.”

“Our findings show that white sharks don’t gather just by chance, but more research is needed to find out why.”

The findings are published in the journal Behavioural Ecology and Sociobiology.

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Adam Schilds et al. 2019. Evidence for non-random co-occurrences in a white shark aggregation. Behavioral Ecology and Sociobiology 73: 138; doi: 10.1007/s00265-019-2745-1