Data will be collected over two years to investigate whether individual white sharks repeatedly visit particular locations off the lower west and south west of WA and the impact of environmental conditions on their numbers.
Our 20 m patrol vessel Hamelin has been commissioned to carry out this important shark research and tagging activity along the WA coast.
White sharks are scarce in WA waters, they are highly migratory and travel vast distances in a short period of time – all qualities making them hard to locate and research. The extension of the Shark Monitoring Network will endeavour to seek out and locate white sharks so we can tag them and can track their future large-scale movements.
The tags being used are called acoustic transmitters which emit a unique coded message that can be recognised by an acoustic receiver or ‘listening station’.
Depending on the tagging activity and situation, acoustic transmitters will either be externally attached in muscle near the dorsal fin using a tagging pole or internally implanted into sharks with a small surgical procedure.
Internally implanting transmitters could maximise the expected battery life of up to 10 years but is a very challenging task and may not be a viable option in all situations.
Any internal tags that are able to be inserted can help researchers estimate shedding rates of external tags.
Acoustic receivers have been fitted to concrete moorings and deployed onto the seafloor and can detect the presence of a tagged shark at about 300 to 400 m.
The placement of acoustic receivers is important. They have been configured in lines extending from the beach (400 m from shore) and across the continental shelf to about 200 m in depth at the following locations; Ningaloo, Rottnest-Perth, Hamelin Bay (Augusta), Chatham Island (Walpole) and Bald Island (Albany). Configuring the placement of receivers in this manner will under most conditions create a continuous line of detection referred to as an ‘array’. Extension of the Shark Monitoring Network has specifically funded the arrays off Hamelin Bay and Bald Island and upgraded the array off Chatham Island.
Having this equipment in the water is only part of the job done. To obtain the stored data from acoustic receivers, this equipment will need to be lifted from the sea floor to the surface, where this stored data can be downloaded, batteries replaced, equipment serviced and redeployed back to the sea floor.
At selected timeframes (every 6 months), receivers will need to be retrieved from the sea floor to download the recorded information, replace batteries and service the equipment. A Remotely Operated Vehicle (ROV) will be obtained to assist the recovery of receivers from the sea floor.
The Shark Monitoring Network project being undertaken here in Western Australia has links to similar activities conducted in South Australia and South Africa. This collaborative approach means that any white sharks tagged outside WA waters that swim past our arrays will be detected, and vice versa. We know through previous studies that white sharks do travel from South Australia to WA and even the odd shark travels from South Africa.
To analyse patterns of white shark movements in Western Australian waters will require enough white sharks tagged and time to collect enough data. The extension of the Shark Monitoring Network is a two year scientific project and a high priority for the Shark Response Unit. Data that we hope to collect, in combination with complimentary shark-related research projects will contribute to build a picture on the movements of white sharks.