Whale Shark Logs Longest-Recorded Trans-Pacific Migration

A female whale shark’s migration from the eastern Pacific to the western Indo-Pacific, spanning a distance of 20,142 kilometers (more than 12,000 miles) has been tracked by researchers, revealing this journey to be the longest whale shark migration ever recorded.

The female whale shark (Rhincodon typus) involved in the study, was tagged near Coiba Island in Panama, a marine protected area off the coast of Central America. STRI marine biologist Héctor M. Guzmánteam and his team of researchers named the shark Anne for conservationist Anne McEnany, president and CEO of the International Community Foundation (ICF). The multi-year project also tagged 45 additional sharks in Panama, in an attempt to collect data on their migratory routes.

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In this study, the whale shark’s position was estimated based on signals from a Smart Position and Temperature (SPOT) tag tethered to the shark, received by the Advanced Research and Global Observation Satellite (ARGOS). The tag only communicates with the satellite when the shark swims near the surface. Anne remained in Panamanian waters for 116 days, then swam toward Clipperton Island,  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, the deepest point on the Earth’s surface almost 11,000 meters (36,000 feet) below sea level. Whale sharks dive to more than 1900 meters (6000 feet). But it is unknown what the animal was doing in this area.

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Whale shark migration routes from Panama to the Mariana Islands (black track) tagged in September 2011 and from Mexico to the Marshall Islands (red track, tagged in September 1995. (a); and details of tracks for Panama (b); eastern Pacific (c); Hawaii (d); Marshall Islands (e), and Mariana Islands (f) – Source: Hector M. Guzman

Among all groups of marine species, seabirds undertake the longest migrations across the oceans, although whales and sea turtles also migrate across vast distances. However, clearly defined migratory routes have not been identified for many fish species, including some migratory shark species, and for many of these pelagic species it is unclear why they travel such long distances.

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?

Whale sharks are the largest fish on the planet, reaching 12 meters (40 feet) in length.

Despite being the world’s largest fish, it’s amazing to me how little we know about this species,” said Scott Eckert, co-author and biology professor at Principia College. “When I first began working on them, their taxonomy was debated, and it still wasn’t clear how they reproduced.”

Genetic studies show that whale sharks across the globe are closely related, indicating that they must travel long distances to mate. Whale sharks have been tracked for shorter distances along similar routes, but this report is the longest-recorded migration to date and the first evidence of a potential trans-Pacific route.

The results of Guzman’s study show the complexity for managing this endangered species as their migratory paths obviously cross multiple jurisdictions, with the protection and conservation measures being mostly focused at local level rather than across the Pacific Ocean.

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There is currently no robust estimate of the global whale shark population. The species is considered endangered by the IUCN due to the impacts of fisheries, bycatch losses, and vessel strikes, combined with its long life span and late maturation. During the past 75 years, it is estimated that nearly half of the world’s whale sharks have disappeared. In many parts of the world, whale sharks have legal protection, but regulations are often not enforced.


Journal reference:

Hector M. Guzman, Catalina G. Gomez, Alex Hearn, Scott A. Eckert. Longest recorded trans-Pacific migration of a whale shark (Rhincodon typus)Marine Biodiversity Records, 2018; 11 (1) DOI: 10.1186/s41200-018-0143-4

 

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