BULL sharks could be using Sydney Harbour as their love nest for mating before travelling up to 1800km to far north Queensland chasing food.

In one of the first major studies of larger bull sharks, 114 have been tagged and are tracked using acoustic tracking devices.

The tagged sharks, ranging in size between 80cm and 3.2m, regularly move across the NSW-Queensland border, travelling between 60km to 1770km across all months of the year.

“Long-range movements are not uncommon in sharks but knowledge of the extent and regularity with which these movements occur is often lacking,” the report said.

“Movements and habitat use by juvenile bull sharks has been well-documented but data on adult movements is limited.”

SHARK LEAPS FROM WATER DURING SURF CONTEST

media_camera A 3m bull shark caught in Sydney Harbour near Clifton Gardens / Picture: Craig Greenhill

The bull shark research, which is ongoing and backed by the DPI and Fisheries NSW, uses 326 acoustic receivers in Sydney Harbour, the Clarence River, Moreton Island, Lady Elliot Island and other locations.

“The longest moves were made by 17 individuals travelling from Sydney Harbour to the northern end of the Townsville reefs, a 1770km straight line distance,” the report said.

“The next most common long distance move was from Sydney Harbour to the Capricorn Bunker reefs (1150km) by nine individuals.”

media_camera A 3m bull shark caught in Sydney Harbour near Clifton Gardens.

The research suggests Sydney Harbour had become a location “used for mating” with a lack of neonates, or baby sharks in the estuary.

Once the bigger sharks, which can live in both salt and freshwater, move offshore, they are less likely to return to estuary mouths and change behaviours as they mature.

“The majority of individuals undertaking long-range movements were large juveniles or adults,” the report said.

The study is also analysing the impact of “no-fishing and no-entry zones” such as marine parks, on adult bull sharks moving along the east coast.

media_camera A 3m bull shark caught in Sydney Harbour near Clifton Gardens.

The data showed many adult bull sharks migrated to hunt off the Great Barrier Reef and the sharks “likely have a key role as large predators in coral reef environments”.

The bull sharks, whose preference for shallow waters make them more dangerous to humans, were caught using long lines and drop lines, with all sharks measured, checked for sex and having a V16 acoustic transmitter surgically implanted.