Ocean Literacy · Shark Research

Whale Shark Tagged Five Times Off Mexico’s Yucatán Tracked for Nine Years and 34,000 Miles

Researchers have fitted the same male whale shark, known as Milo, with a satellite tag five times since 2017. His movements now span more than 3,400 days, from the Gulf of Mexico to waters east of Bermuda and as far north as Massachusetts.

By SEVENSEAS Media | Ocean Conservation

Every summer, whale sharks gather in the Caribbean just off Mexico’s Yucatán Peninsula to feed, and one of them keeps coming back. Milo, a male roughly eight metres long, was fitted with a satellite tag in July 2026 for the fifth time since 2017. The Guy Harvey Foundation, which announced the tagging in September with its partners, says his combined record now covers more than 34,000 miles, about 55,000 kilometres, over more than 3,400 days, and calls it the longest record of any shark’s movements.

Five tags on one fin

The project is a collaboration between the foundation, the Mexican conservation group Ch’ooj Ajauil AC, the Guy Harvey Research Institute at Nova Southeastern University in Florida, and the University of Rhode Island. Individual whale sharks can be told apart by their spot patterns and the shape of the dorsal fin, which is what lets a team working the same aggregation year after year find a particular animal again.

Milo’s first tag, in 2017, sent data for only a couple of weeks, because the team was still refining its attachment method. It fitted new transmitters in 2018, 2020 and 2023, and again this July. Tags of this type log the shark’s position when the dorsal fin breaks the surface. Rafael de la Parra of Ch’ooj Ajauil, who attached the first device, says Milo was the first whale shark he fitted with a real-time, fin-mounted transmitter. “Over the course of nearly 10 years, I have had the opportunity to replace his transmitters several times,” he said.

Long journeys and long stays

Across the five deployments, Milo has moved through the Gulf of Mexico, around the northern Caribbean islands, into the open Atlantic east of Bermuda and up the US coast as far as Massachusetts. Between those runs he has also spent months at a time in small areas, a pattern the institute’s director singles out.

Milo has revealed just how flexible whale sharks can be, demonstrating the capability of enormously far-flung migrations way out into the Atlantic, yet equally content with ‘staying put’ for months at a time in small regions.

Dr Mahmood Shivji, Director, Guy Harvey Research Institute, Nova Southeastern University

Since 2017 the team has deployed 48 fin-mounted satellite tags on whale sharks in the region. The foundation argues that long-term data on where these animals go, and where they linger, is fundamental to conserving the species. Milo’s track and those of other animals tagged by the institute are published on its public map at GHRItracking.org.

What the record measures

The announcement is headlined as a world record for the longest shark track. On distance alone that is hard to square with the institute’s own earlier work. In January 2018 it reported that Andy, a tiger shark tagged in Bermuda in 2014, had covered about 37,565 miles in 1,240 days, and Nova Southeastern’s student newspaper described him then as the longest tracked shark of all time.

The stronger claim is about duration. Milo’s record joins nearly a decade of movement data for one individual, assembled from five separate deployments on an animal the team keeps finding again. Guy Harvey, the foundation’s founder, calls retagging one animal five times and following it for almost a decade “unprecedented”. The release does not explain how the 34,000-mile total was calculated or cite a published study, so the figure is best read as the team’s own running tally.

A feeding ground and a tourism draw

The Yucatán aggregation draws whale sharks and manta rays from across the Gulf and the northwestern Atlantic each summer, when fish eggs and larvae float at the surface. The foundation says numbers at the site fell noticeably in recent years and that the 2026 season brought hundreds of animals a day. The release gives no counts for earlier seasons against which to measure that recovery.

The site is also a busy ecotourism destination, with local boat captains taking visitors out to swim with the sharks. Ch’ooj Ajauil says it studies the effects of that tourism and works with environmental authorities, local guides and tour operators to improve protection for the species.

The IUCN moved the whale shark from Vulnerable to Endangered in 2016, and its assessment found that global numbers had fallen by more than half over 75 years, driven by hunting for meat, fins and oil, accidental entanglement in fishing nets and collisions with vessels. A 2018 institute study in the Maldives, based on a decade of repeated underwater measurements of live sharks, estimated that males can live up to 130 years; this year’s release puts the figure at more than 125. On either estimate, Milo’s nine years of data cover only a small part of one life.

Read the full announcement from the Guy Harvey Foundation and its partners on the Nova Southeastern University newsroom.

SEVENSEAS Media · Conservation Journalism for the Ocean