Shark stomach study reveals surprising diet with bottom-feeding habits
Scientists in Australia have delved into the dining habits of juvenile great white sharks and discovered a humble diet that belies their image as a fearsome predator. After examining the stomach contents of great white sharks captured off the coast of New South Wales, the scientists were surprised to discover bottom-dwelling creatures made up a decent portion of their diets, shedding further light on how and where they spend their time.
The team described the project as the first-ever detailed study of the diets of great white sharks, with the researchers analyzing the stomach contents of 40 deceased juveniles that were collected through protective nets off the eastern coast of Australia.
In doing so, the team found a range of marine creatures made up mealtime for the predators, involving some that were to be expected and some that came as a surprise. Mid-water fish like Australian salmon made up around 32 percent of the sharks’ diet, but the team did not expect to find that bottom-dwelling fish like flathead and stargazers also featured heavily, contributing around 17 percent.
"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,” says Dr Vic Peddemors a study co-author from the NSW Department of Primary Industries.
The study also showed that larger sharks tend to have a diet with higher fat content, while the consumption of low-lying creatures was also found to include different types of rays, along with eels and other fish species.
"White sharks have a varied diet,” says lead author Richard Grainger from the University of Sydney. “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. Eagle rays are also hunted, although this can be difficult for the sharks given how fast the rays can swim."
The researchers say that sharks are unlikely to begin hunting larger prey such as dolphins or other sharks until they reach around 2.2 m (7.2 ft) in length. Their findings are consistent with tagging programs that show white sharks spend much of their time swimming far beneath the surface, with the team hoping these findings will prove useful in better understanding their migratory and feeding habits as a means of conservation.
"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 Grainger. "The stereotype of a shark's dorsal fin above the surface as it hunts is probably not a very accurate picture.”
The research was published in the journal Frontiers in Marine Science.