A team of researchers from the University of Rhode Island and Nova Southeastern University in Florida have been tracking an endangered whale shark named “Rio Lady” with a satellite transmitter for more than four years — a record for whale sharks. sharks and one of the longest tracking efforts for any shark species.
Whale sharks, which live 80 to 130 years, are the world’s largest fish and the third largest creature in the ocean – after the blue whale and the fin whale. The size of a small school bus, they inhabit tropical oceans and swim slowly to the surface, with their mouths wide open, scooping up everything in their path: small fish, fish eggs and plankton. Every year they have to travel about 8,000 kilometers to find enough food to survive. Whale shark populations around the world have declined, mainly due to interactions with humans, to the point where they are now listed on the International Union for Conservation of Nature’s Red List as globally endangered.
Researchers from URI and Nova Southeastern tracked Rio Lady for approximately 43,000 kilometers over nearly 1,700 days between 2018 and 2023. Her journey took her through the Gulf of Mexico, the Caribbean and into the Atlantic Ocean south of Bermuda. A study conducted by the researchers was published in the journal Marine and Freshwater Research, detailing the movement, migration and habitat use of Rio Lady.
“This was an astonishing amount of time to be able to track the movements of a wild animal,” said lead author Daniel Daye, who graduated from URI in May 2023 with a master’s degree in biological and environmental sciences. “Four years of data on the movements of even one individual has allowed us to study whale sharks to an unprecedented degree and explore questions that cannot be answered with shorter tracks.”
Rio Lady was tracked via satellite telemetry using a smart position and temperature transmitter (SPOT) fitted to her dorsal fin. The tag provided location transmissions for four years of her life. Satellite telemetry has revolutionized research into animal movement – especially in marine species – allowing researchers to discover long-term movement patterns and core habitats for marine animals, the study said.
“As the largest fish in the ocean, tracking the movements of whale sharks over long periods of time is challenging,” said Brad Wetherbee, an assistant professor of biological sciences at URI and an expert on shark movement and migration, who provided advice on the project. “But information about the movements of these endangered sharks is important for managing their populations.”
Daye says one of the main challenges in managing large marine species such as the whale shark is that they are difficult to track. Whale sharks travel great distances and routinely dive deep, making studying the full extent of their habitat difficult.
“Because these sharks travel such long distances, it is important to identify where and when the sharks are, and what they are doing in each of these areas,” Daye says. “This way, management can take a more targeted approach so that effort is not wasted on areas where sharks are using habitats elsewhere. Although Rio Lady is just one shark, the extremely long lifespan of the SPOT tag has allowed us to start researching some of these sharks. These questions are answered in more detail with respect to what sharks do from year to year, rather than from year to year.”
Rio Lady was first tagged in 2007 with a pop-up satellite archive tag attached to her near Isla Mujeres, in the waters off Cancun, Mexico, which are visited annually by hundreds of whale sharks from July to August. She was tracked for 150 days before her transmitter went off. She was tagged again in the same area in August 2018 by Rafael de la Parra, executive director of Ch’ooj Ajauil AC, an ocean conservation organization in Mexico. De la Parra also cooperated in the investigation.
During the study, Rio Lady was detected by satellite for 1,687 days – August 30, 2018 to April 12, 2023. During a period of approximately 1,085 days – August 30, 2018 to August 18, 2021 – 1,354 locations were recorded at relatively frequent intervals. In that time she covered approximately 43,000 kilometers, traveling about 40 kilometers per day.
Researchers found that Rio Lady occupied three different regions in the Gulf of Mexico and that the timing of its use of these areas was fairly consistent, Daye said. Between July and August she consistently returned to the waters off Isla Mujeres. In the area known as the Afuera, hundreds of whale sharks gather for the largest gathering in the world: They dine on an endless fish egg buffet, Daye said.
After leaving the Afuera area, few detections were received each year of the survey in autumn and winter. Rio Lady was believed to have traveled south into the Caribbean Sea as far as Colombia for two years before returning to the Gulf of Mexico early this year. Researchers believe Rio Lady’s seasonal migration may be typical of whale sharks that gather off the coast of Isla Mujeres in the summer.
“This unprecedented issue of Rio Lady sheds new light on the long-term consistency of movements and illustrates the kind of information this technology can generate,” said Mahmood Shivji, professor of biological sciences at Nova Southeastern University, who collaborated on the study .
Rio Lady’s onward journey can be followed on the Guy Harvey Research Institute tracking website, click on project 21.
