New research into the international increase in unprovoked shark bites has found a trend of 'regional hotspots', where a heightened number of bites occur over a relatively short timeframe.
The study, by Bond University researchers Dr Blake Chapman and Dr Daryl McPhee, has shed new light on the issue of unprovoked shark bite on humans, which have been climbing steadily globally over the past three decades.
Published in the journal, Ocean and Coastal Management, the research provides an analysis of long-term trends in shark bites, and the potential drivers of these trends, at six global hotspots, including Australia.
Dr McPhee said the trend of shark bites occurring in clusters was evidence that while a degree of chance was involved, unprovoked shark bites were not 'completely random'.
"They are more likely influenced by a set of conditions that increase the likelihood of shark-human interaction at a local or regional scale, and these conditions do not necessarily continue to persist consistently through time," he said.
"Conditions include those that potentially change the overall pattern of human water use, as well as those that alter the distribution and abundance of relevant shark species, such as environmental conditions, climate and water quality, coastal development and changes in prey numbers."
Dr McPhee said many factors came into consideration.
“We need to be clear that unprovoked shark bite is a complex phenomenon, involving several different shark species and an array of human activities over a large geographic area,” he said.
“The results of the research show that in a number of hotspots – in Australia, the US, South Africa, Brazil, Reunion Island and the Bahamas - the prevalence of unprovoked shark bite is increasing, but it still remains a very small source of human injury and fatality and we should not panic or overreact.
“We still remain more likely to be injured by fireworks than we are by sharks.
“More seriously though, surfers are substantially more at risk of serious injuries that have nothing to do with sharks, and these injuries include lacerations to the head; contusions, sprains and fractures; and ruptured eardrums.”
Dr McPhee said while the research added further weight to the logical view that the observed trend of increasing bites was influenced by a growing population, and therefore more people in the water, the researchers found this factor alone was insufficient to explain the trend in all instances.
“There is no single universal cause for increased shark bites, but rather a number of factors are at play, some of which are more relevant at some locations than others,” Dr McPhee said.
“For example, the rapid rise in shark bites at Recife in Brazil could be largely attributed to a large port development which modified habitat and displaced sharks to an area that was very popular for swimming and surfing.
“In the case of a series of bites at a small stretch of coastline in South Africa during 1998, it correlated with warm sea surface temperatures in the western Indian Ocean and a decreased rainfall in the southern part of South Africa.
“An issue that remains unresolved is whether the increased number of bites is due to an increased number of large sharks of key species.
“Logically if there are more sharks of key species such as adult white sharks in the coastal zone then you would expect more bites.
“We are aware that anecdotal information suggests more large sharks are now present in some parts of Australia, but we could not find a body of scientific information to prove this for species such as white and bull sharks, and in fact for tiger sharks the available overall scientific information suggests a continuing decrease.”
Dr McPhee said that ongoing work such as tagging was critical in identifying habitat use of key shark species and work identifying trends in abundance and size of sharks was also important.
“Overall, strategies such as the $16 million NSW Government Shark Management Strategy - which in addition to undertaking important shark tagging work, also has a key focus on the use of emerging technologies to better mitigate the already low risk - provide an important foundation for water users and sharks to co-exist," he said.
“There are technologies for individual protection that have been independently scientifically tested such as electric deterrents that have demonstrated to statistically reduce the probability of a bite.
“For detecting sharks there is also emerging technology including the Shark Alert system which is an aerial surveillance technology that shows significant promise for vastly improving detectability of sharks compared to what can be expected from human observers.”
The new research is an extension of a study completed in 2014, which found Australia recorded the highest number of fatal shark bites globally over the past three decades, with the number of unprovoked bites increasing threefold.
The initial report revealed 32 fatal shark bites had been documented in Australia between 1982 and 2011, more than South Africa (28 fatalities) or the United States (25 fatalities).
At the same time, the total number of unprovoked shark bites in Australia (171) and South Africa (132) was significantly less than that recorded in the United States (769) over the same period.