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Shark hazard mitigation strategies.
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Research & Initiatives
The State Government is supporting a variety of research projects and initiatives to gain a better understanding of shark biology and ecology by implementing (and investigating) various public safety initiatives and making changes to government policy. The aim is to provide everyone with useful information to make informed decisions about their water use.
Shark Tagging06 November 2013
The Department of Primary Industries and Regional Development currently monitors more than 860 acoustically tagged sharks – including 258 white sharks.
Of these tagged sharks, more than 465 bronze, tiger and white sharks may trigger a real time response through our satellite-linked (VR4G) receiver network, notifying response agencies of a potential shark hazard.
Sharks are fitted with acoustic tags which emit a sequence of low frequency ‘clicks’ that give each tag an audible ID number. These unique signals can be detected and recorded when the shark swims within 400-500m of one of the acoustic receivers that have been deployed as part of the Shark Monitoring Network.
In Western Australia researchers have had the most success tagging white sharks when they have been found scavenging on a floating whale carcass, or when around schooling fish such as snapper off Perth.
External tags are attached via a tether to a small stainless steel barb, which is prodded into the shark’s skin using a modified hand spear (or gidgee). However, the limitation with external tags is they may fall off or get damaged. To overcome this issue, Department of Primary Industries and Regional Development researchers aim to capture sharks to internally implant acoustic tags, which allow a shark to be detected for up to ten years.
To capture a shark a single baited hook is suspended from a large, anchored buoy that is monitored continuously. After some initial commotion, a captured shark will soon quieten down enough to be brought alongside the boat.
When safe to do so, experienced research staff secure the shark with suspension ropes and carefully roll the shark onto its back, putting it into a sleep-like state known as ‘tonic immobility’.
A small incision is then made in the shark’s abdomen, the tag inserted into the body cavity and the incision closed with a few stitches. At the completion of the minor surgery the shark is rolled over to wake it up. Even though the process only takes a few minutes, great care is taken to keep the shark’s head and gills in the water so that it can continue to breathe during the procedure.
A plastic ID tag is attached to the dorsal fin as a visual record that the shark has been internally tagged. Details about the shark are recorded such as species, sex, length and a genetic sample is taken. In the case of a white shark, an external acoustic tag is also used. If enough white sharks can be tagged with both internal and external tags, it may be possible to understand the rates at which external tags are shed (i.e. eventually fall off or are damaged).
Once the tagging process is complete, lines are carefully removed and the shark is released.