The dorsal fin above water causes the average Australian’s heart to flutter, but the great white shark (Carcharodon carcharias) does more of its feeding below the surface than previously thought, research suggests.
When a team from the University of Sydney investigated the stomach contents of 40 juvenile sharks it found remains from a variety of fish species that typically live on the seafloor or buried in the sand.
“This indicates the sharks must spend a good portion of their time foraging just above the seabed,” says Richard Grainger, lead author of a paper in the journal Frontiers in Marine Science. “The stereotype of a shark’s dorsal fin above the surface as it hunts is probably not a very accurate picture.”
The new findings are supported by tagging data that shows great C. carcharias spends a lot of time many metres below the surface.
Grainger and colleagues compared their discoveries with published data elsewhere in the world, mainly South Africa, to establish a nutritional framework for the species.
“Understanding the nutritional goals of these cryptic predators and how these relate to migration patterns will give insights into what drives human-shark conflict and how we can best protect this species,” says co-author Gabriel Machovsky-Capuska.
The study found that, based on abundance, the sharks’ diet was about 32% mid-water ocean swimming fish, 17% bottom-dwelling fish, 15% Batoid fish such as stingrays, and 5% reef fish.
The remainder was unidentified fish or less abundant prey. Grainger says marine mammals, other sharks and cephalopods (squid and cuttlefish) are eaten less frequently.
“The hunting of bigger prey, including other sharks and marine mammals such as dolphin, is not likely to happen until the sharks reach about 2.2 metres in length,” he says
The study also found that larger sharks tend to have a diet higher in fat, likely due to their high energy needs for migration.
Tracking of great white sharks shows that they migrate seasonally along Australia’s east coast from southern Queensland to northern Tasmania, and the range of movement increases with age.