Four-year investigation fails to count WA’s sharks

A four-year investigation into the number of white sharks that frequent the WA coast has offered no conclusive results about the size of the population.

The study was prioritised by the State Government after a spate of shark attacks and non-fatal encounters between September 2011 and July 2012 off the WA coast.

The researchers found the abundance of south-western white sharks was one of the factors that contributed to the increase in the number of encounters. But they also reported that the information required to allow them to estimate the population’s size was not available.

The report presented simulated population sizes.

“Depending upon the combination of inputs, the changes in simulated population levels since 1938/39 have varied from essentially no change in their population abundance, moderate declines, through to the population having already declined to extinction,” the report said.

“Currently available methods for quantifying age, growth and reproductive rates require samples from dead sharks, which survey results suggest may be limited to as few as 35 per year in Western Australian fisheries and fewer than 100 per year across all fisheries within the south-western population.”

The report recommended the collection of genetic samples to help estimate the size of the population.