A study from the University of Sydney is providing new insight into the diets of great white sharks. In the first detailed assessment of great white predatory behavior off the east of Australia, experts have discovered that the sharks spend more time feeding along the seabed than previously thought.
Study lead author Richard Grainger is a PhD candidate at the Charles Perkins Centre and School of Life and Environmental Sciences.
“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,” said Grainger.
“The stereotype of a shark’s dorsal fin above the surface as it hunts is probably not a very accurate picture.”
The research represents an important step toward understanding the feeding and migratory habits of the great white shark.
“We discovered that although mid-water fish, especially eastern Australian salmon, were the predominant prey for juvenile white sharks in NSW, stomach contents highlighted that these sharks also feed at or near the seabed,” said study co-author Dr. Vic Peddemors.
According to Grainger, the findings are supported by tracking data that show great whites spending a lot of time many meters below the surface.
The experts analyzed the stomach contents of 40 juvenile great white sharks caught in the NSW Shark Meshing Program. The findings were compared with published data from South Africa and other regions to establish the feeding patterns of great whites.
“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,” said study co-author Dr. Gabriel Machovsky-Capuska.
The study revealed that, based on abundance, the great white’s diet primarily consisted of mid-water ocean swimming fish, such as Australian salmon; bottom-dwelling fish, such as stargazers; and batoid fish, such as stingrays.
A small percentage of the sharks’ diet included reef fish, and the remainder was made up of unidentified fish or less abundant prey.
“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,” said Grainger.
“We found that rays were also an important dietary component, including small bottom-dwelling stingrays and electric rays. Eagle rays are also hunted, although this can be difficult for the sharks given how fast the rays can swim.”
“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 meters in length.”
The researchers also found that the diets of larger sharks are higher in fat content, which is needed for energy during long migratory journeys.
“This fits with a lot of other research we’ve done showing that wild animals, including predators, select diets precisely balanced to meet their nutrient needs,” said study co-author Professor David Raubenheimer.
Tracking data showed that great whites migrate seasonally along the east coast of Australia from southern Queensland to northern Tasmania, and the range of movement increases with age.
The study is published in the journal Frontiers in Marine Science.