Great white sharks spend more time feeding close to the seabed rather than at the surface, reveals new research.
The first-ever detailed study of the diets of the feared predators – made infamous by the movie Jaws – conducted off the east coast of Australia surprised scientists as they appear to spend more time than expected hunting at the bottom of the sea.
The findings were published just hours after a 10-foot great white killed a surfer off northern New South Wales (NSW), the third fatal shark attack in Australian waters this year.
Researchers found great whites love to feed on salmon and other bony fish including eels, whiting and mullet, as well as bottom-dwelling stingrays and electric rays.
Scientists say that understanding how sharks feed is vital for managing their interaction with humans.
Study lead author Richard Grainger, a PhD candidate at the University of Sydney, said: ‘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.
‘The stereotype of a shark’s dorsal fin above the surface as it hunts is probably not a very accurate picture.’
Experts say the study, published in the journal Frontiers in Marine Science, is an important contribution towards understanding the sharks’ feeding and migratory habits.
Dr Vic Peddemors a co-author from the NSW Department of Primary Industries (Fisheries), said: ‘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.’
Mr Grainger said: ‘This evidence matches data we have from tagging white sharks that shows them spending a lot of time many metres below the surface.’
The study examined the stomach contents of 40 juvenile white sharks (Carcharodon carcharias) caught in the NSW Shark Meshing Programme.
The scientists compared the fidnings with published data elsewhere in the world, mainly South Africa, to establish a nutritional framework for the species.
Study co-author Dr Gabriel Machovsky-Capuska, an adjunct Senior Research Fellow at the University of Sydney, said: ‘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.’
Mr Grainger said: ‘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.
‘Eagle rays are also hunted, although this can be difficult for the sharks given how fast the rays can swim.’
The study found that the sharks’ diet relied mostly on pelagic, or mid-water ocean swimming fish, such as Australian salmon (32.2 per cent), bottom-dwelling fish, such as stargazers, sole and flathead (17.4 per cent), reef fish, such as eastern blue gropers (five per cent), and batoid fish, such as stingrays (14.9 per cent).
The remainder was unidentified fish or less abundant prey.
Mr Grainger said that marine mammals, other sharks and cephalopods – squid and cuttlefish – were eaten less frequently.
He aded: ‘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.’
The scientists also found that larger sharks tended to have a diet that was higher in fat, likely due to their high energy needs for migration.
Co-author Professor David Raubenheimer, Chair of Nutritional Ecology at the Iniversity of Sydney, said: ‘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.’
Tracking of 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.
Dr Peddemors added: ‘This study will give us a lot of information to assist in this management process.’
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