Materials & Methods

Capture - Old Technique
A baited barbless hook was used to pull the shark towards the back of the vessel where a tail rope was attached in water and the hook removed. Ropes were then looped around the pectoral fins to raise the shark to expose the dorsal fin.

Capture - New Technique
The new technology involves attracting sharks to a small boat using bait. As the shark approaches, a tail clamp called the 'Shark Claw' is applied to the shark's tail using a three metre pole. The claw is attached to a rope and a large float. The drag of the float quickly immobilizes the shark usually in less than 60 seconds. The immobilized tiger shark can continue to pump water across its gills. This new technique greatly reduces stress on both the tiger shark and researcher.

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Tagging

Once the shark is captured it is secured to the duck board of the research vessel by the tail. A strap is placed around the animal behind the pectoral fins, and the shark is raised in a horizontal position with the dorsal fin just out of the water.

The satellite tag consists of an ARGOS satellite transmitter, long life batteries, an aerial, and a saltwater switch, all in a waterproof resin pod. It is streamlined in design and weighs very little in water. Therefore it will not interfere with the tiger shark as it swims.

The transmitter sends a unique identifying code via radio waves to polar orbiting satellites that are fitted with ARGOS receivers. The signal from the tag is then sent to a receiving station in France where the tag's position on the earth's surface is calculated. CMR scientists receive the positions and plot the shark's track. Radio waves do not travel very well through seawater, so the tag will only transmit to the satellites when the aerial is out of the water.
 

 
On average, the tag transmits the tiger's position every two to three days. The accuracy of the position depends on how long the aerial is out of the water. The best positions can place the shark to within 150 m. The saltwater switch on the tag ensures that it does not transmit when underwater, thereby saving battery power.

Two tags types are being used on the tiger sharks :

SPOT tags - give position data only when the shark is on the surface
"Nicole" was the first shark to use this type of tag

SPLASH tags - give position data as well as uploading depth profiles of the shark swimming activities.
Used since 2007 on RAINEBOW only

Once the shark has been tagged, measured, and a tissue sample taken, the shark is released. The tiger shark is pushed through the water for a few minutes until it starts swimming under its own power.