Satellite tags: True James Bond gadgets
There are different kinds of tags researchers use for gaining information about animals. But none of these are as exciting as "near-real time satellite tags". James Bond would have loved this high-tech tool which allows us to track the shark day-by-day and almost on a real-time basis. Every time the shark comes to the surface of the sea and its dorsal fin breaks the water, the tag switches on and sends a radio signal that is picked up by passing polar-orbiting environmental satellites carrying the Argos System. The very special "character" of white sharks makes this type of tracking easier: great whites spend a lot of time at the sea surface hunting marine mammals and inspecting floating objects and are therefore more likely to be observed on the surface than most sharks.Once the radio transmission sent by the tag is picked up the satellites estimate the position of the tag and then re-transmit this message to land-based Argos Centers where the information is processed. The global position of the tag and any data it might have sent is then sent directly to our computers via email, or we can get it directly from web-based database. The entire procedure takes about an hour or two, thus the 'near' real time name of these tags. In this way, we can keep an up-to-date track of where the white sharks are day to day with only a few hours delay.
Two types of near-real time satellite tags
We use two types of near-real time satellite tags, SPOT tags and SPLASH tags. SPOT tags (Smart Position and Temperature Transmitting tags) give us information on the position of the sharks and on the ambient temperatures the shark has experienced in the previous 24 hrs; SPLASH tags (Data Collecting Argos Satellite tags) give us the same information as SPOT tags but in addition they also provide data on the depth where the shark has been in the 24 hrs previous to the message being sent. More precisely, every time the shark's fin breaks the water surface a "salt-water" switch senses that the instrument is out of the water, and turns the tag on allowing it to transmit its signal to the satellite in a matter of milliseconds, then turns off again as soon as it gets wet again, thus saving precious battery time. However, for a given transmission to be received, a satellite needs to be passing over the shark exactly at the same time that the transmission from the tag is being sent. Each satellite "pass" lasts typically about 15 minutes maximum in any point on earth. This is why many times days go by without us hearing from the sharks.How is the tag put on the shark?
As everybody can imagine it is quite challenging to attach a satellite-tag to the dorsal fin of a great white shark. It requires a lot of careful planning and experience to ensure that the handling of the sharks is done in a safe and efficient way that includes the less possible amount of damage to the shark . Stress for the sharks needs to be minimized and permanent or major damage to their health or life has to be strictly avoided during our work. Although great whites are huge and fierce looking animals they are quite sensitive and need to be handled very carefully. At the same time the team has to make sure that the tags are securely attached and the safety of the researchers is also guaranteed.First the shark is attracted to our research boat using chum and bait. Once the candidate shark to be tagged (we choose on the basis of size trying to tag smaller sharks first and larger ones later as the team gets comfortable and gains experience) is selected, it is caught with bait and a specially designed double-hook (sharks used to routinely bend-open our single hooks!). Because the health of the sharks is a top priority, the team has a highly skilled fisher that places the hook right on the corner of the jaw so that the shark does not swallow the hook and gets hooked by the stomach. The fisher lets the shark try to escape but a large buoy attached to the fishing line makes the shark get tired after a period of 10 to 15 minutes. Once the shark is sufficiently tired, the fisher brings it to the tagging boat where the scientific team puts the shark into a metal cradle after a minimum struggle and in great shape. The cradle itself is used to lift the sharks out of the water and restrain their movements while the scientific team fits the shark with the satellite tags.
A world's first in shark health-care and safety
Once the sharks are in the cradle there is an expert shark veterinarian taking care of the sharks' health at all times. First, a hose with pumped and aerated seawater is placed in the shark's mouth providing a constant flow of water over the gills and maintaining the sharks' oxygen supply. Then the veterinarian injects the shark with several medications including antibiotics and vitamins to help it overcome the stress of capture.During this time the rest of the scientific team securely fixes the satellite tag to the dorsal fin of the shark using nylon pins that pass through holes that are drilled into the shark's dorsal fin, and which are secured with metal nuts and washers. The tags have been designed not to remain permanently attached to the sharks: the combination of metals chosen for the nuts and washers ensures that they will corrode after several months eventually causing the tag to fall off and letting the sharks heal.
Formula-1 Pit stop action
Before returning the sharks to the water the hooks are cut and completely removed, leaving only a small wound that will heal in a few weeks leaving no permanent damage to the sharks. Overall, the team has managed to consistently handle white sharks of up to 4 meters in length and 750 kg of weight in only about 14-16 minutes total time, from hooking to the freeing of the shark with transmitters in place; typical times out of the water in the cradle run from 7 to 10 minutes only. Extremely detailed and careful planning, experience and coordinated team-work make possible this action worthy of a Formula-1 race pit stop.» Further information about tagging sharks can be found here.
