A team of dedicated researchers from the University of Rhode Island and Nova Southeastern University in Florida have successfully tracked a 26-foot endangered whale shark, affectionately named “Rio Lady,” using a satellite transmitter for an impressive duration of over four years – setting a record for whale sharks and marking one of the lengthiest tracking efforts for any shark species.
With a lifespan ranging from 80 to 130 years, whale sharks are not only the largest fish in the world but also the third largest creature in the ocean, surpassed only by the blue and fin whales. These gentle giants, comparable in size to a small school bus, inhabit tropical oceans and leisurely glide near the water’s surface, feeding on small fish, fish eggs, and plankton with their mouths wide open.
Whale sharks cover about 5,000 miles annually in search of sufficient food to sustain themselves. Due to human-induced impacts, whale shark populations have markedly decreased, leading to their classification as Globally Endangered on the International Union for Conservation of Nature Red List.
The remarkable journey of Rio Lady spanned approximately 27,000 miles and lasted nearly 1,700 days from 2018 to 2023. This incredible migration took her through the Gulf of Mexico, the Caribbean, and into the Atlantic Ocean south of Bermuda. A comprehensive study featured in the journal Marine and Freshwater Research delves into the movement, migration, and habitat utilization of Rio Lady.
“This was an amazing length 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 about the movements of even a single individual has allowed us to investigate whale sharks to an unprecedented degree and investigate questions that can’t be answered with shorter tracks.”
Rio Lady’s movements were meticulously tracked via satellite telemetry, utilizing a smart position and temperature transmitter (SPOT) attached to her dorsal fin. Over the course of four years, the tag provided invaluable location transmissions. The use of satellite telemetry has considerably enhanced our understanding of animal movements, particularly among marine species. This technology has enabled researchers to unravel long-term movement patterns and identify crucial marine animal habitats.
The whale shark Rio Lady. Credit: University of Rhode Island
“As the biggest fish in the ocean, it is challenging to follow the movements of whale sharks over long periods of time,” said Brad Wetherbee, assistant professor of biological sciences at URI and an expert on shark movement and migration, who consulted on the project. “But information on the movements of these endangered sharks is important for the management of their populations.”
Managing large marine species like the whale shark presents a significant challenge due to their elusive nature. These majestic creatures cover long distances and frequently dive deep, making it a challenging task to comprehensively study their habitat.
“Since these sharks travel such great distances, it’s important to identify when and where the sharks are located, along with what they are doing in each of these areas,” said Daye. “This way, management can take a more targeted approach so that effort isn’t wasted on areas where sharks are using habitats elsewhere. While Rio Lady is only one shark, the extremely long lifespan of the SPOT tag has allowed us to start examining some of these questions in more detail regarding what sharks do on a year-to-year basis, rather than a single year.”
Rio Lady was initially equipped with a pop-up satellite archival transmitter in 2007 near Isla Mujeres, a location off Cancun, Mexico, where hundreds of whale sharks gather annually from July through August. This tagged shark was tracked for 150 days before the transmitter detached. In August 2018, Rio Lady was re-tagged in the same area by Rafael de la Parra, the executive director of Ch’ooj Ajauil AC, an esteemed ocean conservation organization in Mexico. De la Parra’s collaboration on this study further strengthens the efforts to study and protect these magnificent creatures.
The study continuously tracked Rio Lady by satellite for 1,687 days, from August 30, 2018, to April 12, 2023. During a span of about 1,085 days, from August 30, 2018, to August 18, 2021, researchers recorded 1,354 locations at regular intervals, revealing that she journeyed approximately 27,000 miles, covering an average of 25 miles per day.
Researchers discovered that Rio Lady occupied three distinct regions in the Gulf of Mexico, and her utilization of these areas was consistently timed. Specifically, between July and August, she consistently returned to the waters near Isla Mujeres. In the area known as the Afuera, hundreds of whale sharks gathered for what was identified as the largest gathering of its kind worldwide, feasting on an abundant fish egg “buffet.”
Following her time in the Afuera area, there were fewer detections during the autumn and winter months each year of the study. It is believed that Rio Lady traveled south into the Caribbean Sea, as far as Colombia, for two years before returning to the Gulf of Mexico early in the year. Researchers suggest that Rio Lady’s seasonal migration may be typical for whale sharks that aggregate off the Isla Mujeres in the summer.
“This unprecedented track of Rio Lady sheds new light on long-term consistency of movements and illustrates the type of information that this technology can generate,” said Mahmood Shivji, professor of biological sciences at Nova Southeastern University, who collaborated on the study.
Journal reference:
Daniel Daye, Rafael de la Parra, Jeremy Vaudo, Jessica Harvey, Guy Harvey, Mahmood Shivji and Bradley Wetherbee. Tracking 4 years in the life of a female whale shark shows consistent migrations in the Gulf of Mexico and Caribbean. Marine and Freshwater Research, 2024; DOI: 10.1071/MF23147
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