Great White Sharks Tracked by Satellite

PAT Tags - a revolution in marine animal research

Pop-up archival tags (PAT tags) are one of the most exciting recent developments in electronic instrumentation for the study of large marine animals and perfect for white sharks. Dr. Bonfil has successfully used these instruments for almost 5 years, first in South Africa and now in New Zealand. In fact his greatest discovery, the transoceanic migration of white sharks across the entire Indian Ocean was made thanks to one of these sophisticated instruments. Nicole, a 3.8 m total length female white shark was tagged by Dr. Bonfil and his colleagues in Gansbaai, South Africa, in November 2003 and the shark travelled all the way to the west coast of Australia in less than 3 months, offering a number of great discoveries and establishing new records for white sharks. Some of the media splash that this discovery caused can be seen in the following links:

• No shark tale: Great white swam 12,000 miles (MSNBC)
• Great white's marathon sea trek (BBC)
  

What exactly is a PAT tag?

PAT tags are basically microchips with sensors and a transmitter encased in microphone-shaped epoxy body. They are approximately 17 cm in length, with a float and antenna on one end and a flexible cord with a plastic dart at the other end. The dart is used to attach the tag to the shark. These high-tech instruments measure and store the depth, temperature and light levels of the sharks’ surroundings every minute for the entire length of time they are attached to the shark. At a pre-chosen date and time –which are programmed into the tags directly by the researchers- the tags stop data collection and free themselves automatically from the shark and then float to the surface. Once at the ocean surface, the tag starts sending transmissions containing the collected data to ARGOS instruments mounted on environmental satellites that have polar orbits. The great advantage of these tags is that they are capable of relaying a summary of the stored data to the research team without being recovered, therefore increasing the likelihood and ease of obtaining the data. On the other hand, if by a mere miracle one of the tags is physically recovered (it happens once in while!), the entire data set that was collected by the tag can be downloaded to gain a lot more detailed information about the shark's movements during the time it had the tag attached to it.

The approximate latitude and longitude of the sharks' whereabouts each day can be estimated using the light level data collected by the PAT tag. The light level data allows us to know the length of the day and this is an approximation of the latitude; the time of midday or midnight can also be estimated from the light level data and this is used to estimate the longitude. Mathematical geo-location algorithms are used for these estimations of latitude and longitude and allow researchers to reconstruct the approximate path that the shark followed between the point where it was tagged and the location where the tag released itself and started transmitting from the surface.

Putting a PAT tag in a white shark

The method to attach a PAT tag to a shark in the field is very simple. First the shark is attracted to the surface close to Dr. Bonfil´s boat using chum (a mixture of fish oil, fish meat and water) and baits without hooks. Once the shark begins circling the bait, the researchers pull the bait closer to our boat, and using a modified hand harpoon they insert the dart at the end of the PAT tag into the back of the shark. The ideal place to put the dart is on the upper back of the shark just below the posterior part of the first dorsal fin. The sharks only feel a little pinch when the 1-inch plastic dart is inserted, like when we get an injection, and many times the sharks don’t even seem to notice that we darted them. Usually the hardest part is to find the white sharks in the ocean and make them come to our bait.

An incredible amount of very useful information

PAT tags tell us a great deal about the vertical and horizontal movements of great white sharks and the temperatures they sustain. Using these instruments Dr. Bonfil discovered that the great white can dive to depths of at least 980 m!, and also that during oceanic travel they swim very close to the surface, as if looking at the position of the sun. This led Dr. Bonfil to speculate that white sharks might use their powerful vision to guide themselves in their long voyages across entire oceans by using celestial bodies like the sun or the moon. PAT tags also tell us a lot about the relationship between water temperature and the behaviour of white sharks; so far they have shown to have a great tolerance for changes in temperature that range from 3.4˚ to 25˚ C! But most importantly, PAT tags tell us where the sharks travel, which are their most favoured areas of the ocean, and what routes they follow during their migrations. All of this is key information to help governments and scientists to design better protection measures for these fantastic creatures of the ocean.  

» Further information about tagging sharks can be found here.