Incredible Journeys: Migratory Sharks on the Move
Even as scientists rush to identify the migratory paths of some endangered shark species to help better protect them, climate change and other threats shift this behavior, adding urgency to the research.
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Migration: Many animal species do it — from tiny zooplankton to enormous whales — moving over every continent and through all oceans, from north to south, south to north, Europe to Asia, and Asia to Africa. This movement by individual animals in response to season or life stage typically involves substantial numbers and vast distances.
Recent studies give scientists a better understanding of migrations at the species and population levels and reveal implications for conservation. This series focuses on a few particular species, what we’re learning about their migrations, and how that knowledge may help us protect them.
We start with a group of species many people may not realize migrate: sharks.
In April 2025 researchers tagged a 7-foot male scalloped hammerhead shark they dubbed Webbkinfield off Port Aransas, Texas. Over the next four months, the scientists watched, fascinated, as Webbkinfield pinballed around just off the continental shelf. He didn’t wander far on the map but swam almost 2,000 miles.
Less of a homebody, a male shortfin mako named Pico was tagged in March 2018 off the Texas coast and traveled more than 21,000 miles by August 2020. His journeys took him up to Massachusetts and back. Twice.
Scientists are learning that some sharks get around more — a lot more — than others. A silky shark tagged June 18, 2021, in the Galápagos Marine Reserve had swum more than 1,000 miles west into the open ocean by Sept. 20; another tagged that February traveled more than 8,000 miles into the big blue and back. Others milled around the reserve, with a few making short forays to the Central or South American coast.
Silky shark satellite tagging in the Galapagos. Photo: Pelayo Salinas, used with permission.
This research on when and where marine animals move is critical to efforts to protect them, says Yannis Papastamatiou, an associate professor in Florida International University’s Institute of Environment.
“Conservation is expensive, so we need to know when, where, and how to apply actions,” he says.
Papastamatiou is one of the more than 350 contributing authors of a recent study in the journal Science that aims to tackle part of that challenge. The study examined data on migration patterns of more than 100 large-bodied marine vertebrate species, including several sharks.
One of the study’s biggest revelations: On average, data showed, the tracked animals spent just 13% of their time inside existing marine protected areas.
That suggests a pressing need to protect more ocean habitats and figure out the best areas to protect.
Some efforts along these lines are already underway. For example, in 2022 the nations that are parties to the United Nations Convention on Biodiversity adopted the Kunming-Montreal Global Biodiversity Framework, which set a goal to protect, conserve, and manage at least 30% of the world’s oceans. But Papastamatiou stresses that it needs to be the right 30%. “A lot of these animals move over very large areas, and it is not feasible to protect all of those.”
Research on three shark species help illustrate the challenges ahead, as well as what we still need to understand about shark migration.
Shortfin Mako
Mako shark populations have plummeted due to commercial and recreational fishing, which is they they’re listed on Appendix II of the Convention on International Trade on Endangered Species, which puts limits on their commercial exploitation.
Makos are an apex predator found in tropical and temperate waters around the world, but until recently little was known about their movements and, therefore, where to protect them.
But earlier this year, a genetic study identified two distinct mako populations in the North and South Atlantic, according to co-author Mahmood Shivji of the Save Our Seas Foundation Shark Research Center at Nova Southeastern University, Florida. Females appear to stick to their respective populations, but males contribute genetically to both, which means they move between them. Such intermixing helps maintain genetic diversity, Shivji points out, giving the species a better chance to adapt to environmental changes.
This new information builds on a 2021 tagging study by the Harte Research Institute at Texas A&M University Corpus Christi (which included Pico) that showed makos spend more time in the northwestern Gulf of Mexico than expected. Another found that some stay in the Gulf year-round.
“We thought makos were seasonal in the Gulf from looking at catch data,” said Kesley Banks, an associate research scientist at the institute and an author on both papers. “We assumed they left in the summer and that isn’t the case. With both these studies, we see that they stay in the Gulf all year.”
Not all of them, though. In addition to Pico’s summer sojourns up the Atlantic coast, another male traveled thousands of miles to and around the Caribbean. Mako sharks tagged in the Atlantic by Shivji and his colleagues have not been tracked to the western Gulf, though, according to Banks.
These findings highlight how much movement patterns vary even within a species and make it clear that highly migratory animals must be managed at a large scale, not just on the local level. Those two meandering makos from the Gulf, for example, passed through at least 12 jurisdictional boundaries, representing different levels of fishing pressure and a variety of regulations.
Scalloped Hammerheads
Critically endangered scalloped hammerhead sharks are another highly migratory species experiencing intense overfishing and rapidly diminishing numbers.
Every year hundreds of these hammerheads, mostly females, gather around protected areas near the Galápagos Islands. It isn’t clear where they migrate from, though, or whether the same individuals return every year. To find out, the Florida Shark Research Center spent five years conducting biopsies collected from the aggregation. They’re currently analyzing the samples, with plans to publish results in mid-2026.
Researcher about to deploy a satellite tag on a scalloped hammerhead. Photo: Mark Wong, used with permission.
But we already know a few things about their behavior.
“The sharks aggregate during daytime and disappear at night,” probably to feed, says Shivji, who is leading the study. The researchers suspect many of the females are pregnant based on their size, and tracks show some moving from the aggregation to recently discovered nursery areas near the mainland. Others have gone westward far into the Pacific, although their tags didn’t last long enough to show whether those individuals turned around and came back.
This study could help make the case that the paths the sharks travel between existing protected areas also need protection.
“Their migrations to the aggregation area put them at risk,” Shivji says.
Silky Sharks
Considered “vulnerable to extinction” by the IUCN, silky sharks get their name from the sheen created by densely packed dermal denticles — the tooth-like structures that make up shark skin. Once one of the most abundant shark species, they are heavily fished for their fins.
Silky sharks aggregate around Cocos Island in Costa Rica and the Galápagos Marine Reserve. Individuals tagged there by Shivji’s team mostly remained close by, not venturing far outside the Reserve. But some were tracked far into unprotected international waters, with the data indicating they faced fishing pressure on as much as 50% of their journeys.
Shivji and colleagues also have tagged silky sharks in Revillagigedo National Park, part of a network of protected areas in Mexico’s Eastern Tropical Pacific (and a UNESCO World Heritage Center). Those, too, traveled well outside the protected area, with two known to have been captured.
One question answered by this work could be whether the Galápagos and Mexico populations mix and if so, whether their travel routes that can be protected.
More to Learn
Researchers have learned a lot about shark migrations in the past few decades thanks in part to improved and more commonplace tools. Tags are more advanced, for example, providing near real-time tracking via satellites for longer periods of time thanks to protective paint and better batteries.
Even so, findings have only scratched the surface. The movements of many species remain a mystery, as does the variation in migration behaviors within a species.
“People like to describe migration as a population-level reaction, where everybody leaves at same time, all go here, and all come back at the same time,” Papastamatiou says. “But we have started to see it is a proportion of animals that perform a migration, with a mix of animals that migrate or are residential. It is important to ask what determines who migrates and who remains? There has to be some selective reason for it.”
Studies have shown sex differences in migratory patterns of some shark species, such as females seeming more likely to migrate than males and pregnant females more likely to migrate than nonpregnant ones.
A Moving Target
Even as scientists are learning shark migration patterns, those patterns may be changing.
Another paper on which Shivji is a co-author found mako migrations responding to increasing water temperatures and the decreased dissolved oxygen content that results. Because makos have the highest metabolic rate of any shark, low oxygen levels effectively restrict their range.
“People focus on water temperature with climate change, but dissolved oxygen should be as big a concern,” Shivji said.
Other research has concluded that elevated sea-surface temperatures could cause sharks to delay their departure for summer habitats. That may already be happening; from 2011 to 2021, researchers at Florida Atlantic University saw blacktip shark populations off the state’s coast decrease to one-tenth of their initial abundance.
“In 2011 it was common to see over 10,000 sharks on a single aerial survey flight along Palm Beach County,” FAU professor Stephen Kajiura wrote in an email. “By 2021, we barely saw 1,000, despite increasing the number of flights in later years. The sharks were shifting northward. During that time, the average winter water temperature had increased by 1 degree C. That is a dramatic shift in just a decade.”
Such changes in the behavior of major predators have wide-ranging effects on local ecosystems.
For example, fewer sharks preying on groupers and snappers could increase their numbers, and those fish would eat more of the smaller fish. Reducing the number of smaller fish could increase that of other creatures down the food web, in turn causing changes to their prey. Down at the bottom of the chain, a decline in species that eat blue-green algae could increase toxic algae blooms.
In addition to protected areas, mitigation strategies also must account for changes in movement patterns. For example, a shift in timing of the arrival of a species to an aggregation could necessitate altering existing fishing limits.
Enforcement is also key — and already inadequate.
“Law enforcement is stretched out. We need more funding and more people,” said Banks. “But we also need the research to know where to send people, to narrow down where enforcement should be.”
Toward that goal, she and other scientists plan to continue tagging sharks.
“I’m waiting on tags in the mail right now,” Banks says. “Shark science is in its infancy, we are just now learning where they’re going and making new discoveries.”
“There are still species that we don’t know much about,” Papastamatiou says. “And even those we do know about, we can’t stop studying them because they can change.”
Previously in The Revelator:
Trump vs. Birds: Proposed Budget Eliminates Critical Research Programs
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