Author: “The stereotype of a shark’s dorsal fin above the surface as it hunts is probably not a very accurate picture.”
SYDNEY — Great white sharks have struck fear in the hearts of swimmers and beach goers for decades, but what do these ferocious fish usually snack on? The diets of great whites living off the coast of east Australia were analyzed by a group of scientists from the University of Sydney, and the team behind the study was surprised by what they found.
These kings of the sea seem to eating a whole lot more food found close to the seafloor than researchers expected.
“Within the sharks’ stomachs we 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 lead author Richard Grainger, a PhD candidate at the Charles Perkins Centre and School of Life and Environmental Sciences at the University of Sydney, in a release. “The stereotype of a shark’s dorsal fin above the surface as it hunts is probably not a very accurate picture.”
Salmon are usually the dinner of choice for adolescent great white sharks in that area, but these findings clearly reveal that sharks tend to spend a lot of time deep in the sea near the ocean floor.
“This evidence matches data we have from tagging white sharks that shows them spending a lot of time many metres below the surface,” Grainger adds.
In all, the stomach contents of 40 adolescent white sharks were analyzed. That information was then cross referenced against data collected on great white sharks from other regions of the planet, mostly South Africa. All of this information was used to construct a nutritional framework for great white sharks.
“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,” explains study co-author Dr. Gabriel Machovsky-Capuska, an adjunct Senior Research Fellow at the Charles Perkins Centre.
“White sharks have a varied diet. As well as east Australian salmon, we found evidence of other bony fish including eels, whiting, mullet and wrasses. We found that rays were also an important dietary component, including small bottom-dwelling stingrays and electric rays,” Grainger comments. “Eagle rays are also hunted, although this can be difficult for the sharks given how fast the rays can swim.”
Based on their research, the study’s authors concluded that the average adolescent great white shark’s diet consists of 32% mid-water ocean swimming fish like salmon, 17% bottom-dwelling fish like flatheads or stargazers, 5% reef fish, and just under 15% batoid fish (stingrays).
Those estimates, of course, depend on the availability and abundance of species in a given area.
“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,” Grainger notes.
It was also noted that bigger sharks usually have diets that are higher in fat, probably because larger sharks need more energy for migration.
The study is published in Frontiers in Marine Science.