pop-up satellite tags

The most loyal among our public will surely remember how desperate we were last year, when we had to leave without our precious (in every sense of the word) satellite tags, which were malfunctioning. Luckily this year the tags work, and were the first items we stored in the bag on the eve of our departure.
The tags we use are Pop-Up satellite tags, a.k.a PAT tags, which stay attached to the animals up to a year and automatically detach on a set date. Once they reach the surface, thanks to an in-built float, they start transmitting the data to the Argos satellite system, which will email the results back to us.
During the time they are attached to the animal, the tags will record several information like water temperature and the depth at which the shark swims. They also record the light levels and from this, through a complicated calculation, we shall be able to pinpoint the position of the animal on the map every single day. The position is not extremely accurate, but since there are no alternatives (the GPS positioning system obviously does not work underwater!), that will do.
These tags are hi-tech and equally hi-priced. Why did we invest so much money (we have three, at 3.500 USD each plus taxes) in them? First of all because we can watch our sharks for a very limited time (21 out of 265 days); and only when they are within our visual range and, in any case, after the sun sets we can no longer follow them. All the info we gather during our stay are limited to the days we can spend in this fabulous bay, and to the hours that we spend in the water.
We do not know what they do after the sunset or where they spend the rest of the year ? that?s where the PAT tags play their role. The other reason why we decided to invest that much money in these three PAT tags, is that results obtained from similar instruments have radically changed the existing knowledge on some species of sharks. As an example, it was always believed that the basking shark hibernated and stopped feeding during the winter time: but British scientists demonstrated, thanks to PAT tags, that that is not the case. Basking sharks are constantly on the move and search for maximum concentration of their food, the plankton. Information gathered via PAT tags on great white sharks were equally important: conventional knowledge had it that this predator never ventured much farther from the coast. It turned out that they travel thousands of miles off-shore and even spends months at a time in the open ocean, away from any land.
What do ?our? sharks do? We know for sure they are capable of very long migrations: the record for a sandbar shark was 3700 km! But if you want to know, keep following our study during this wintertime, when all PAT tags will finally come off the sharls. We will be anxiously waiting for the messages relayed by the Argos satellite systems. But for the moment, we are waiting for the return of our sharks, and the arrival of Jimmy, our ?tagger?.

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