St. Helena Whale Shark Tag

St. Helena Whale Shark Tag

A lot of a whale shark’s daily life is still unknown. Things as basic as their reproductive habits to how they use the water column throughout the day are still a mystery to researchers. One tool used to help find answers to these questions are satellite tags. Georgia Aquarium has used satellite tags to study whale sharks in Mexico, the Galapagos islands and in St. Helena in the South Atlantic Ocean. Satellite tags have a pretty rough life, though. They are relentlessly exposed to tropical sunlight while immersed in a corrosive seawater environment. The tags are designed with these conditions in mind to take some abuse and still report their observations. However, current tags aren’t designed with deep dives - like the ones whale sharks around St. Helena make in mind. The island of St. Helena rises very quickly from the ocean depths and within a few nautical miles of shore, you’re easily in depths of 1000 meters. The tags Georgia Aquarium uses for whale shark research are rated to survive depths of up to 1800 meters without being damaged from this crushing pressure. Unfortunately, a lot of the tags deployed were damaged during these extreme dives. Fortunately, though, there were two tags that successfully reported their movements and a third true-life message in a bottle story.

On March 5, 2017, biologist Flora Zauli, a member of a beach patrol at Espiritu Santo, Brazil, found a device in the sand. She brought it to Dr. Larissa Pavanelli who identified the item as a satellite tracker and was able to decipher the label on the tag and contacted Harry Webb. After Harry was given the coordinates and time of day where the tag was found, he plotted the course using Google Earth and learned that the tag drifted over 2,200 miles in 421 days. It is presumed that the tag detached prematurely from the whale shark and washed ashore after its oceanic journey. Looking through records, it appears that this tag never reported any data and may have been defective. However, all is not lost. Once we receive the tag at Georgia Aquarium, it may have a treasure trove of valuable data stored on it that can be retrieved once it’s connected to a computer. The greater revelation is that this incident can be used to help understand more how the ocean current moves from St. Helena towards the east coast of Brazil. This information helps us when we look for locations where whale sharks might be found. They are known for following the prevailing currents and not working against them to conserve energy. With this tag, there is now a connection from St. Helena to the beach at Espiritu Santo, Brazil. Because whale sharks are known to migrate large distances and can be found all over the globe, it’s important to identify potential “hot spots” or areas of interest to focus our efforts. Were it not for the beach patrol finding and reporting this tag, this new area of interest might have never been established.

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