How scientists monitor whale sharks
26-foot-long ‘Rio Lady’ has satellite tracking tag
Rio Lady, a 26-foot-long female whale shark, is one heck of a wanderer. Scientists are learning she is quite a teacher, too.
Last month, Rio Lady sent up a satellite signal from the warm waters of the Gulf of Mexico. It was the latest “ping” of a journey that covered thousands of miles in less than two years. Along the way, a team of researchers monitoring her progress is working to unlock the many mysteries of one of the world’s largest creatures.
Rio Lady is unique and has a long relationship with her observers. She first was tagged by a team of researchers in August 2007 near Isla Mujeres, an island off the coast of Cancun, Mexico, on the northeastern tip of the Yucatan Peninsula.
The waters there draw massive numbers of tiny baitfish and plankton each May through September.
Huge numbers of whale sharks gather to feast on them.
The annual migration has made it a popular spot for divers, who charter boats for the chance to see these gentle giants up close. Scientists have used the gathering as an opportunity to study the sharks.
Rio Lady, when she was first encountered, had a huge girth, leading the team that tagged her to believe she was pregnant. They used a satellite pop-off tag designed to detach after five months. The tag popped off 5,000 miles away, in the southern Atlantic Ocean between Brazil and Africa.
Researchers believe she went there to give live birth in deep waters to an estimated 200 to 300 pups that grew from eggs inside her.
Scientists don’t know how many times whale sharks give birth during their 100-year lifespan, and no one has reported seeing them mate.
9,621 miles in 620 days
Since 2011, Rio Lady has been an annual visitor to Isla Mujeres, and since August 2018, scientists have had more accurate information about her position in real time.
That’s because researcher Rafael de la Parra, of the Mexican conservation organization Ch’ooj Ajauil, attached a new Smart Position and Temperature (SPOT) satellite tracking tag to her dorsal fin. He’s the one who attached Rio Lady’s first tag in 2007.
Rio Lady has crisscrossed the Gulf of Mexico from Texas to Mexico to Florida’s Panhandle to the Caribbean. She’s logged 9,621 miles over 620 days, entering as many as five nation’s waters, said Mahmood Shivji, a professor at Nova Southeastern University’sHalmos College of Natural Sciences and Oceanography and the director of its Guy Harvey Research Institute.
“It makes you wonder where else she explored during the years she wasn’t being tracked,” Shivji said. “But one thing that makes her so unique is that she is perhaps the only marine animal which has been tagged twice.”
Rio Lady and eight other whale sharks, as well as other satellite-tagged sharks, marlins and sailfish, can be followed at ghritracking.org.
Whale sharks are filter feeders, like baleen whales. The docile creatures drift along with the ocean currents in the warm tropical seas of the world. They cover great distances to take in enough food to survive. They occasionally can be seen by anglers and divers as they swim slowly in waters off Florida’s coasts. They spend most of their time in solitude, except when they congregate to feed in areas such as Isla Mujeres.
Lessons
Because of their size, because they spend most of their time in the upper part of the water column and because they are found in seas that are calm much of the time, whale sharks are endangered, according to the International Union for Conservation of Nature.
Whale sharks are harvested for their meat, fins and oil. In addition to being overfished, they are sometimes victims of ship strikes.
Many countries have begun to protect them from fishing, but not all.
To better protect whale sharks for future generations, Shivji said Nova Southeastern and collaborating researchers Mote Marine Laboratory, the Georgia Aquarium and Ch’ooj Ajauil are studying many aspects of a whale shark’s life.
“The more we learn about these animals, their growth dynamics, where they go, what areas may be their nurseries, it can lead to a better understanding of their life history, which is imperative to guide conservation efforts,” Shivji said.
“As for Rio Lady, it will be interesting to see when or if she goes back to the feeding aggregation and where she goes after that,” he said.
Some of the greatest whale shark mysteries yet to be unlocked are where they mate, where and how exactly they give birth and where the young spend their first years, since so few are encountered.
Rio Lady may be the whale shark that one day gives scientists those answers.