More Australians have been killed in unprovoked shark attacks this year than in any year since 1934.
But the total number of shark bites is in line with the annual average over the past decade. It is prompting experts to consider whether the La Niña weather event, associated with cooler sea surface temperatures in the central Pacific, may be affecting where sharks search for prey.
On Sunday, police in Western Australia called off their search for the body of Andrew Sharpe after pieces of the 52-year-old father’s wetsuit and surfboard had washed up on the beach near Esperance. Friends saw a shark bite him two days earlier.
His death was the seventh from a shark bite in Australia in 2020 and the sixth from an unprovoked attack.
According to the Australian Shark Attack File, it has been 86 years since six people last died from unprovoked shark bites in a single year.
In 1929, nine people died from unprovoked shark bites in Australia – a record that preceded debate about introducing the first shark nets at Australian beaches several years later.
Dr Phoebe Meagher, the wildlife conservation officer with the Taronga Conservation Society Australia who manages the Australian Shark Attack File, said the six deaths from unprovoked bites this year was well above Australia’s 50-year average of 1.02 deaths a year, but the general shark bite numbers were looking “smack bang on average”.
There have been 17 unprovoked shark bites so far in 2020, the same as last year and one fewer than in 2018. In 2015, there were 22.
Dr Blake Chapman, a marine biologist who examined shark neuroscience for her PhD, told Guardian Australia that understanding how a shark behaved when attacking was important in determining its intent. She said repeated bites suggested the shark was treating a human as prey.
“In some of the cases this year it sounds like the shark hung around and bit more than once, which is unusual behaviour for great white sharks,” she said. “When they bite more than once it’s more likely to be fatal as there’s more blood loss.”
However, she noted some fatal attacks had been single bites on the upper part of the leg, groin or near the abdomen, leading to greater blood loss from key arteries and vital organs.
She said great white sharks, which have killed several of this year’s victims, “tend to follow migrations of prey”, such as salmon, which can be influenced by a La Niña event.
“We do tend to see little spikes in shark bites in La Niña ,” she said. “For great white sharks, if we see them bite someone once and then leave, it suggests they were maybe curious and weren’t in the area for prey, because there is nothing stopping a shark from eating a person.”
Chapman said different Australian jurisdictions investigated and recorded varying levels of detail about an attack. Combined with the relatively small number of deaths, it made it hard to definitively understand the causes behind the increased death toll this year.
Prof Robert Harcourt, the director of Macquarie University’s marine mammal research group and a researcher of shark behaviour, said that in addition to cooler water temperatures being favourable to great white sharks, increased rains during a La Niña could reduce salinity and attract bull sharks to waters where more people swim.
He said currents and winds could also lead to salmon and other fish clustering closer to the shore than under other conditions.
“The sharks are responding to where their prey will most likely be,” Harcourt said.
In January, a 57-year-old experienced diver, Gary Johnson, was killed by a shark near Esperance in Western Australia, and in April, a 23-year-old wildlife ranger, Zachary Robba, was killed by a shark off the Great Barrier Reef.
In June, Rob Pedretti, 60, died after he was bitten by a shark while surfing in northern NSW, and in July, a teenager died from a shark bite while surfing at another beach in the region.
In September, 46-year-old Nick Slater died after being bitten while surfing near the Gold Coast.
While surfing is not considered provoking a shark, the death of a 36-year-old while spearfishing off Queensland’s Fraser Island in July is considered to be the result of a provoked bite, as the release of fish blood attracts sharks.