Great White Mystery

Telemetry

Animal telemetry studies allow scientists to collect a variety of information using acoustic or satellite-based sensors called tags. They are mainly used to make migration patterns of pelagic species visible. The resulting movement maps allow definitive conclusions to be drawn about the animals' way of life and history.

Not only horizontal migrations are made visible by the tags, but also the notoriously difficult-to-trace vertical movements of marine species. For example, we now know that male Great White Sharks dive up to 1,200 metres off Guadalupe, while females stay much shallower. Each of these pieces of information is a small mosaic piece in the picture of “shark as mystery” – the increasingly precise tagging technologies allow us to complete this picture bit by bit.

For a long time, it was assumed that sharks have a very limited social structure; the image of the shark as a loner persists. Here, too, the tag data are the basis for a change in our understanding of the animals. Intensity and length of inter- and intraspecific interactions are recorded, revealing a complex picture of mating behaviour, social hierarchies and prey interactions.

Telemetry studies around the world have provided important insights into the movement and behavioural ecology of sharks. This knowledge now forms the basis for developing effective conservation strategies for these endangered animals. For example, the tagging studies allowed the expansion of the protection zones for white sharks in the North Pacific. Not only their breeding grounds off the coasts of North America are now protected, but also their aggregation points off Guadalupe.

Used Tags and technologies

Two types of sensors are used in the research of Guadalupe: VEMCO Mobile Transceiver (VMT) and Sonotronics MiniSUR.

The VEMCO Mobile Transceiver (VMT) is a hybrid between a transmitter and receiver, so it can not only send data to stations, but also receive data from them. Communication is possible with all common VEMCO-coded devices, and transmitters from other manufacturers can also be registered.

The detection range varies from a few 100 metres in coastal waters to 1 kilometre in the open ocean. The VMT can operate at depths up to 1000 m and is suitable for studies in deep water environments.

In the North Pacific, there are many fixed receiver stations as well as numerous stationary objects such as FADs or buoys equipped with VEMCO-coded transmitters. This allows conclusions to be drawn about migration routes and the respective residence times of the sharks. Information on the interaction with other tagged animals is also stored. This allows researchers to better understand the social structures of sharks.

Sonotronic's Miniature Submersible Ultrasonic Receiver (MiniSUR) tags were also equipped with underwater cameras (FinCams) to collect more information about the behaviour of great white sharks off Guadalupe. Image data is mainly used to identify untagged sharks and prey.

Tagging procedure

Great White Sharks are lured to the research boats using bait. Depending on the type, the tags are attached directly from the boat or by free divers in the water. Both types are anchored to the dorsal fin of the animal; the VMT tags are pierced with the help of a harpoon, the MiniSUR are clamped directly to the fin with a clamping device. Neither method of attachment is known to have any negative effects on the sharks.

When removing the tags, however, the two sensor types differ. The MiniSURs detach from the animal after 12 days at the latest and float to the surface – thanks to an integrated buoyancy body. Based on satellite signals, they can be found and collected promptly. The data is read out after the tags have been successfully found.

The VMT tags remain on the shark for up to 10 months. The tags are removed in the same way as they are attached, either by free divers or by hand from a boat. Removal also poses no risk to the sharks. The data is stored and utilized by read-out devices. If it is not possible to remove the tag after 10 months – for example, because the animal has not returned to Guadalupe – the tag remains on the shark, but stops collecting data as soon as the integrated batteries are exhausted. The shark does not suffer any disadvantages by leaving the tag in place.

Unfortunately, tags are lost on a regular basis, whether through accidental detachment due to territorial fights and mating behaviour, changes in migration routes or the death of the animal.