In a span of 48 hours, a 12-year-old boy, an 11-year-old boy and two male surfers were attacked by sharks in New South Wales as of Tuesday. Of them, three shark attack incidents took place at Sydney beaches.
Dr Amy Smoothey, a fisheries scientist and shark expert, examined the images of the bites and confirmed to The Guardian that bull sharks (Carcharhinus leucas) were responsible for all of the attacks.
"Bull sharks have distinct, broad and overlapping triangular cutting teeth in their upper jaw and more slender teeth in their lower jaw," she said.
Sydney witnessed heavy rainfall over the last weekend, where certain areas received more than 50mm within a few hours. The rainfall had triggered a large amount of fresh, yet murky water to enter the coastal areas, including the beaches. This made the coast a conducive place for smaller fishes to reach the spot for foraging.
With bull sharks spending their early days in estuaries before entering the ocean and possesing ability to tolerate water with less salinity, they reached the spot to feed on the smaller fishes gathered there.
Increased levels of biological productivity led to an increase in prey abundance, therefore attracting predators.
Simply said, bull sharks came to feed on the smaller fishes that reached the coast as rainwater flushed into the coasts, and mistook the individuals swimming or surfing along the coast as prey, leading to the attack.
"Rainfall in the catchment affected space use for all teleost species and both sexes of sharks with varying temporal responses. Male sharks responded most promptly to high rainfall, moving upstream in less than 1 day, followed by teleosts between two to seven days and female bull sharks after four days," a paper titled Environmental Drivers of Fine-Scale Predator and Prey Spatial Dynamics in Sydney Harbour, Australia, and Adjacent Coastal Waters highlighted.
The paper also added that the environmental luminosity affected male shark dispersal and space use, likely pointing out the use of visual cues for foraging.
Also, a paper titled Investigating the functional role of an artificial reef within an estuarine seascape: A case study of yellowfin bream (2018) said that prey abundance and distribution are important factors influencing the movements of marine predators.
Notably, 60 shark bite incidents had taken place between 2000 and 2019 in New South Wales. All of Sydney’s northern beaches are closed, and authorities urged people to stay out.