Whale shark logs longest trans-Pacific migration

By on 14 May, 2018

Image by Kevan Mantell.

A single whale shark has been tracked over a 20,142-kilometre journey from the eastern Pacific to the western Indo-Pacific ocean. 

Whale sharks are the world’s largest living non-mammalian vertebrate, and the world’s biggest fish. Named for their sheer scale, they filter-feed in a manner similar to whales, but breathe through gills.

Found in warm, tropical and sub-tropical waters, it is thought that around 25 percent of the global population live primarily in the Atlantic, while 75 percent live in the Indo-Pacific. Genetic studies show that whale sharks across the globe are closely related, suggesting that they must travel long distances to mate. Their long life span and late maturation contributes to their endangered status, along with fisheries impacts, by-catch losses and vessel strikes due to their large size.

Despite rafts of unique biological and evolutionary features, and wild popularity with tourists and divers who flock to swim with the gentle giants — relatively little is known about the species within the scientific community.

But recent research has revealed an extraordinary journey, which may shed new light on the activities of this rare ocean behemoth.

Héctor M. Guzmán, a marine biologist with the Smithsonian Tropical Research Institute, tagged a female whale shark near Coiba Island in Panama, the largest island off of the coast of Central America, a National Park, World Heritage Site and marine protected area. His team named the animal Anne, after conservationist Anne McEnany.

“We have very little information about why whale sharks migrate,” Guzmán said. “Are they searching for food, seeking breeding opportunities or driven by some other impulse?”

Image by Kevan Mantell.

Anne was tagged with a Smart Position and Temperature (SPOT) transmitting tag, one of the most sophisticated and capable animal tracking tags, that communicates with the Advanced Research and Global Observation Satellite (ARGOS) constellation. SPOT tags are typically used to track marine animals that stay close to the ocean surface, so Anne’s tag was equipped with sensors that would only allow it to transmit when close to the surface, when the satellites are within transmission range.

Anne remained in Panamanian waters for 116 days, then swam toward Clipperton Island (France), nearing Cocos Island (Costa Rica) en route to Darwin Island in the Galapagos (Ecuador), a site known to attract groups of sharks.

266 days after she was tagged, the signal disappeared, indicating that Anne was too deep to track. After 235 days of silence, transmissions began again, south of Hawaii. After a nine-day stay, she continued through the Marshall Islands until she arrived at the Marianas Trench, a canyon in the ocean floor near Guam in the Western Pacific where the deepest point on the Earth’s surface was measured, at almost 11,000 metres below sea level.

“Whale sharks in Coiba have already changed their behavior to avoid the surface and tourists,” Guzmán said. “These studies are critical as we design international policy to protect transboundary species like the whale sharks and other highly migratory marine species.”

Guzmán’s data were used to design and draft local and regional policies for the protection of the species: Panama’s Executive Decree No. 9, signed in 2009, prohibits fishing, capture and sale of whale sharks in local waters. In 2014, Panama’s environmental authority passed an additional resolution regulating whale shark watching in Coiba National Park and the Isla Canales de Afuera marine reserve.

It is estimated that nearly half of the world’s whale sharks have disappeared in the last 75 years. Declared endangered in 2016, they are protected in many jurisdictions, but regulation is not often enforced, and they are sought for their fins, meat and teeth.

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