Sharks elude tagging efforts

A month-long program of long-lining to capture and tag white sharks in the Capes region has failed to tag any sharks to date.

The program, part of a two-year extension of the Department of Fisheries Shark Monitoring Network, started more than two weeks ago and aimed to understand the movements of white sharks.

It involved Fisheries staff undertaking 10-day trips, with a high turnover of staff, to maximise exposure to handling and tagging sharks in a safe manner.

Department of Fisheries shark response unit manager Michael Burgess said experience has shown tagging white sharks in WA waters was difficult as they were highly mobile and scarce.

While there were known shark aggregation areas in South Australia near large seal and sea lion colonies, there were no such areas in WA.

“To tag white sharks in WA waters, we are required to develop innovative methods, actively fish for them and enhance our response to opportunities following reported sightings,” he said.

Mr Burgess explained that the option being employed at present involved using long lines over a big area consisting of many hooks and bait and being left overnight.

“In opportunistic situations, it’s possible to get close enough to a shark and attach the tag via a pole spear without needing to capture it by hook,” he said.

While white sharks have remained elusive, Mr Burgess said staff have captured and tagged some big dusky whaler sharks during the long-lining activity.

The department is undertaking a separate tagging program investigating commercially important species such as gummy, whiskery, dusky and sandbar sharks.

He emphasised this month-long program was only the first intensive fishing effort, and the department would be enhancing its responsiveness to opportunistic tagging attempts.

Meanwhile, a University of Western Australia research project into shark repellents has revealed they may work best if they targeted specific species rather than attempt to deter all types of sharks.

Winthrop Professor Shaun Collin said understanding the basic neurobiology and neural basis of shark behaviour might help in the development of effective shark repellent devices.

“We cannot begin to understand how to develop deterrents under different conditions without a basic understanding of these senses and the thresholds to detect objects and weak electric fields in the shark’s natural environment,” he said.

“Three of these papers emphasise the fact that each species of shark is different, and their senses are refined for different purposes under different environmental conditions.”

Professor Collin said the results might indicate the need to target a variety of senses at a range of thresholds rather than aim for a “blanket” repellent.