Last updated October 28, 2019 at 4:28 pm
Researchers have discovered that sharks pick their buddies and stick with them for years.
Why This Matters: “I am a nice shark, not a mindless eating machine” – Bruce from Finding Nemo.
Apex marine predators choose who they hang with and even form communities, new research reveals.
Although normally solitary predators, white sharks gather in large numbers at certain times of year in order to feast on baby seals.
These groupings, scientists had assumed, were essentially random – the result of individuals all happening to turn up in the same area, attracted by abundant food.
Now, however, researchers have used photo-identification and network analysis to show that many of the apex predators hang out in groups which persist for years.
Like us, sharks pick their buddies
To make the findings, Flinders University researchers including Charlie Huveneers, Adam Schilds and Leila Nazimi, spent four and half years taking multiple photographs of almost 300 white sharks gathered around a seal nursery in the Neptune Islands in the Great Australian Bight. The research team also included colleagues from Macquarie University, French Government research organisation CNRS, and South Australia’s Fox Shark Research Foundation,
Through the images they were able to identify individual animals and, to their surprise, found that many were seen in proximity to specific others far more often than chance would determine.
“You’d typically expect all white sharks to match their presence with prey availability, but for some reason not all white sharks visit to and use of the Neptune Islands correspond to periods when seals are most abundant,” says Huveneers.
“Although white sharks aggregate at the study site (Neptune Islands Group Marine Park in South Australia) all year around, the same individuals do not remain at the Neptune Islands throughout the year.”
For example, some sharks are sighted at the Neptune Islands during summer, while others are mostly sighted in winter, even though seal pups that are most vulnerable to white shark predation start venturing in the water around late autumn early winter.
Scientists aren’t sure why they group together
“What is interesting and what our study shows is that within the groups of sharks, some sharks tend to be observed together more regularly that you’d expect by chance,” Huveneers says.
“We still don’t know why this is the case, but some individuals seem to use the Neptune Islands at the same time and to prefer some individuals more than others.”
“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,” says Stephan Leu from 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.”