Rio Lady's movements, migration allow researchers to 'investigate whale sharks at a unprecedented degree'
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| Rio Lady, a mature female whale shark |
A team of researchers at the University of Rhode Island
and Nova Southeastern University in Florida have been tracking a 26-foot
endangered whale shark – named “Rio Lady” – with a satellite transmitter for
more than four years – a record for whale sharks and one of the longest
tracking endeavors for any species of shark.
Whale sharks, which live from 80 to 130 years, are the world’s largest fish and third largest creature in the ocean – behind blue and fin whales.
The size of a small school bus, they inhabit tropical oceans and swim slowly near the surface, with their mouths wide open, scooping up whatever’s in their path – small fish, fish eggs, and plankton. Annually, they need to travel about 5,000 miles to find enough food to survive.
Whale shark populations worldwide have declined, primarily as a result of interactions with humans, to the point where they are now listed on the International Union for Conservation of Nature Red List as Globally Endangered.
Researchers
at URI and Nova Southeastern tracked Rio Lady for about 27,000 miles over
nearly 1,700 days between 2018 and 2023. Her journey took her through the Gulf
of Mexico, the Caribbean and out into the Atlantic Ocean south of Bermuda. A
study conducted by the researchers was published in the journal Marine
and Freshwater Research, describing movement, migration and habitat
use 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 was tracked by satellite telemetry using a smart-position and temperature
transmitter (SPOT) affixed to her dorsal fin. The tag provided location
transmissions over four years of her life. Satellite telemetry has
revolutionized the study of animal movement – particularly with marine species
– allowing researchers to uncover long-term movement patterns and core areas
for marine animals, the study says.
“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 management of their populations.”
A
primary challenge in managing large marine species, such as the whale shark,
said Daye, is that they are hard to follow. Whale sharks travel great distances
and routinely dive deep, which makes studying the full extent of their habitat
difficult.
“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 when 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 first tagged in 2007 with a pop-up satellite archival transmitter
affixed to her near the Isla Mujeres, in waters off Cancun, Mexico, that are
frequented by hundreds of whale sharks annually from July through August. She
was tracked for 150 days before her transmitter popped off. She was re-tagged
in August 2018 in the same area by Rafael de la Parra, executive director of
Ch’ooj Ajauil AC, an ocean conservation organization in Mexico. De la Parra
also collaborated on the study.
During
the study, Rio Lady was detected by satellite over 1,687 days – Aug. 30, 2018
to April 12, 2023. For a period of about 1,085 days – Aug. 30, 2018 to Aug. 18,
2021 – 1,354 locations were recorded at relatively frequent intervals. In that
time, she traveled about 27,000 miles, covering about 25 miles a day.
Researchers
found that Rio Lady occupied three distinct regions in the Gulf of Mexico and
timing of when these areas were used was pretty consistent, Daye said. Between
July and August, she consistently returned to the waters near Isla Mujeres. In
the area known as the Afuera, hundreds of whale sharks aggregate for the
largest gathering worldwide – dining on an endless fish egg “buffet,” said
Daye.
After
leaving the Afuera area, few detections were received during autumn and winter
each year of the study. Rio Lady was believed to travel south into the
Caribbean Sea, as far as Colombia for two of the years, before returning to the
Gulf of Mexico early in the year. Researchers believe 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.
Rio
Lady’s continued journey can be followed on the Guy Harvey Research Institute tracking
website, click on project 21.
