More research by the CSIRO will be needed before an ongoing debate about shark management can come to an end.
The CSIRO’s recent report on the national shark population has triggered concern over Western Australia’s shark mitigation effort, but that has been based on an unclear picture of numbers in the state.
A report released earlier this month found the study used new genetic analysis to measure white shark populations off Australia’s coastline.
However, while governments and the media have seized on various aspects of the report, the scientist who spearheaded the research, Richard Hillary, says it’s not that clear cut.
CSIRO reported there were two main populations studied – the eastern population from Rockhampton in Queensland to east of Bass Strait, and the southern-western population, ranging from west of Bass Strait around South Australia and Western Australia as far north as Ningaloo Reef.
Using biopsy samples taken from juvenile sharks, Dr Hillary and the CSIRO team analysed the genetic profiles of the animals to determine the number of half-brothers and sisters within the samples, to estimate the number of adults based on reproductive behaviour.
The latest research, ongoing since the 1990s, estimated there to be around 750 adult white sharks within the east (with a range of 470 to 1,030) and 5,460 sharks in total.
Adults in the south-west area were estimated at 1,460 (with a range of 760 to 2,250).
Due to inadequate information on breeding grounds in the west, which Dr Hillary said would be a focus going forward, the total population was unable to be determined.
Environment Minister Josh Frydenberg said the WA government ought to do more to protect its citizens against what appeared to be double the number of white sharks in the east, referencing drumline and net approaches used in other states.
But WA Fisheries Minister Dave Kelly said more research into the southern-western population was needed.
“On several occasions, I have asked the federal environment minister to commit more funding for research into the southern-western white shark population,” he said.
In the east, 214 juvenile samples were collected, while 175 were taken in the west. This also meant that the uncertainty range in the west was greater than in the east.
“We’re trying to get innovative about how we can find those juveniles in the west, so there are some possibilities to do with drones,” Dr Hillary said.
WA Greens marine spokesperson Diane Evers said the broad estimate by CSIRO referred to a single population of sharks that roamed off WA, SA and western Victoria.
“So in other words, rather than being a ‘shark capital’ per kilometre of coastline, there are fewer great white sharks off WA than there are off Australia’s east coast,” she said.
At this stage, CSIRO did not have enough information on the location of white shark habitats to comment on density, Dr Hillary said.
He said further research was needed to determine the effectiveness of shark protection measures.
“If a policy comes forward and government wants to do something like additional netting or drumlines, then now we have a basis to analyse what that would actually do,” Dr Hillary said.
“The initial drumline trial that the previous WA government tried to get up was knocked back primarily because we just didn’t know what it was going to do.”
New measures
New shark-deterrent technology is the most recent mitigation approach undertaken in WA.
Freedom 7 by Shark Shield, a diving, spearfishing and kayaking product, qualifies for a $200 rebate from the state government, although the scheme currently fails to cover products designed for surfers.
A potential solution to that gap could soon be surfing-specific shark deterrent Rpela, made by local surfer and board maker Dave Smith, along with another product by Shark Shield.
Both products are currently undergoing testing in South Australia by Flinders University and will qualify for the state rebate if found effective, with a report to be released around April this year.
Mr Smith said his product created an electromagnetic field, which hindered the sensors on the nose of the shark, causing discomfort.
“There’s an anode and a cathode set one metre apart at either side of the board and they put out between 10 and 15 pulses every second,” he said.
Sharks turn away within 1.5 metres of a board with Rpela built in, Mr Smith said.
Mr Smith said he had been a board maker for 30 years and a surfer for more than 40, and believed deterrents such as his were more effective for shark mitigation than drumline and culling measures.
