A report into a test of the device at Dunsborough last summer suggested 22 possible sites for the enclosures but also identified problems with installing them at some beaches.
Report author and Hydrobiology WA manager Phil Whittle said Scarborough had damaging surf and the beach sloped significantly.
‘Cottesloe receives significant swell in winter, so an enclosure could be damaged if it’s left out there,’ Mr Whittle said.
‘It’s (also) a significant surfing spot, making it less attractive, but it could be put out there in summer when it’s calmer.’
The report identified WA’s busiest beaches as Mullaloo, with up to 20,000 swimmers on a summer’s day, Cottesloe (11,000), Fremantle’s Port Beach (9900) and Scarborough (9000).
Mr Whittle said the list of suggested sites was not a ranking and was derived from analysing wave frequency, tide height and beach use for sites.
Mullaloo was not included as a possible site for the nets because the list was not ‘exhaustive’. Protected beaches at Fremantle, Yanchep Lagoon, Safety Bay and Mandurah Marina had good suitability for enclosures.
Mr Whittle said the report being considered by the Government found the 300m by 100m net installed in the shallow waters of Dunsborough was easily installed and removed, did not collect weeds and could be cleaned.
However, problems with drilling piles to secure the structure had added to an initial $200,000 estimated cost and $50,000 may be needed for annual maintenance.
Mr Whittle said stingrays and dangerous fish were trapped by the |enclosure, which was fixed with weights at the net’s bottom and tied to the piles.
‘I have no doubt that future nets would have these weights and ties, and I think it would get cheaper as you engineer out the problems and faults,’ he said.
Mr Whittle rejected Surf Lifesaving WA criticism that enclosures were dangerous and said surfers and jet-skiers already faced and coped with current navigation hazards.
‘We wouldn’t be expecting surfers to ride waves through the enclosures anyway,’ he said.
The Government is considering the report as well as a potential metropolitan site.