La Niña rains are feeding a baby bull shark boom along east coast, says scientist

Could a weather phenomenon affect the number of sharks along Australia’s east coast?

Absolutely, says Bond University associate professor of environmental science Daryl McPhee.

A La Niña event, which Australia is experiencing, is typically associated with wetter-than-average conditions for northern and eastern Australia, particularly in certain months that include summer.

According to Professor McPhee, significant rains often lead to an increase in shark activity and sightings, as swollen rivers and creeks flush food sources into estuaries.

“Particularly in summer, we certainly do start to see more sharks, particularly bull sharks in coastal waters,” Professor McPhee said.

“It’s a very productive time [after rain] and we see lots of sharks because there’s good feed on offer.”

Bull shark swims over the top of a diver
Bull sharks are known to breed in warmer months, and are particularly active in estuaries.(Supplied: Jayne Jenkins )

He said this time of the year was also breeding season for bull sharks, meaning there are many more juvenile sharks about.

“There’s a mullet moving in and out of the river mouths with the rain and other species. It’s also the time of the year for the bull sharks to be breeding,” he said.

“So female bull sharks move into the estuaries this time of year during the late summer months to give birth, and then there’s lots of small sharks that are growing in those river systems, and over time they will disperse as they grow.

“So you would definitely expect to see more bull sharks this time of the year, adjacent to river and creek mouths.”

Popular creeks a bull shark nursery

Professor McPhee said the broadwater around Runway Bay, Tallebudgera Creek and Currumbin Creek were well-known spots for shark sightings and breeding, particularly near any openings to the ocean.

“The first thing that a just-born bull shark does is try and swim upriver as fast as it can get away from mum, because mum has a tendency of eating the children,” he said.

“Bull sharks try to find as much shallow water initially as possible then they start to feed and move around a bit more until they become larger sharks and gently move out of the river systems, but they do move in and out of the river systems as well over time.

bridge over water
The Gold Coast’s popular Tallebudgera Creek is a breeding ground for bull sharks.(ABC Gold Coast: Dominic Cansdale)

Professor McPhee said the activity should decline by about April to May.

“You expect to see a change in the marine system with the onset of westerly winds, which generally occurs April and May, so that’s a period of time where you get a shift,” he said.

“You start to get less rainfall and you start to get a shift from a summer-dominated inshore coastal system to the fall-winter system, so there should be large numbers of sharks hanging around with our weather system of tomorrow with the La Niña system .

“The rainfall should be hanging around creek and river mouths for at least a couple more months.”

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