Where Great White Sharks Go to Feed Surprises Scientists

Researchers investigating the diet of great white sharks living in the waters off the east coast of Australia have shed new light on how these apex predators feed.

According to a study published in the journal Frontiers in Marine Science, the sharks have a varied diet, and they likely spend more time searching for food closer to the seabed than previously thought.

In eastern Australia, white sharks mainly inhabit coastal or shallow waters between the state of southern Queensland and northern Tasmania, with the majority of these animals being juveniles. However, despite local conservation and management efforts, scientists had not characterized the diet of the sharks in this region.

To address this, the scientists conducted the first ever detailed study of the diets of great whites off the east coast of Australia by examining the stomach contents of 40 juvenile white sharks that were captured in a local shark management program.

This analysis revealed that around 32 percent of the diet of the sharks was made up of fish found in the open or mid-water ocean, such as Australian salmon. Next up were bottom-dwelling fish, such as stargazers, sole or flathead fish, making up just over 17 percent of their diet.

These two groups were followed by batoid fish, such as stingrays, and reef fish, like eastern blue gropers, making up nearly 15 percent and 5 percent of the shark's diet respectively.

The scientists say that the remainder of animals detected were unidentified fish, less abundant prey and animals that were eaten infrequently, such as marine mammals, other sharks and cephalopods—a group containing squid and cuttlefish.

"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," Richard Grainger, lead author of the study from the School of Life and Environmental Sciences at the University of Sydney, said in a statement.

"The stereotype of a shark's dorsal fin above the surface as it hunts is probably not a very accurate picture."

"This evidence matches data we have from tagging white sharks that shows them spending a lot of time many meters below the surface," Grainger said.

According to the study, rays form an important part of the sharks' diet, including small, bottom-dwelling stingrays and electric rays.

great white shark
Stock image: A great white shark near the Neptune Islands, South Australia. iStock

"Eagle rays are also hunted, although this can be difficult for the sharks given how fast the rays can swim," Grainger said.

Because the animals examined in the study were all juveniles, the researchers say that the findings can be considered representative of juvenile white sharks.

"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 [7.2 feet] in length," Grainger said.

The study revealed that the larger juvenile sharks tended to have a diet that was higher in fat, which could perhaps be explained by the fact that they need more energy to travel larger distances.

"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," David Raubenheimer, a co-author of the study from the University of Sydney, said in the statement.

Tracking data shows that sharks living off Australia's east coast participate in seasonal migrations from southern Queensland to northern Tasmania, and as the sharks get older their range of movement usually increases.

In the study, the researchers compared their data to similar research from other parts of the world, notably South Africa, helping to shed light on the nutritional needs of the species.

"Understanding the nutritional goals of these 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," Gabriel Machovsky-Capuska, another co-author of the study from the University of Sydney, said in the statement.