In the vast, blue expanse of the Pacific Ocean, shortfin mako sharks—sleek, lightning-fast predators—are running into an unexpected roadblock. These endangered speedsters, known for zipping through the seas at up to 45 miles per hour, are being hemmed in by an invisible fence, and scientists have just cracked the code behind it.
Torpedo of the seas (Maris Kazmers / Sharksong Photography / Granted by source)
A groundbreaking study led by Dr. Michael Byrne from the University of Missouri’s College of Agriculture, Food and Natural Resources is pulling back the curtain on why mako sharks, the racecars of the ocean, aren’t venturing where they used to, and it’s all about one critical factor: oxygen.
Makos need lots of oxygen
Mako sharks are the rock stars of the shark world. With their torpedo-shaped bodies and crescent-shaped tails, they’re built for speed, chasing down prey like tuna and squid with the precision of a guided missile. Shortfin makos, the focus of Byrne’s research, can grow up to 13 feet long and weigh as much as a small car—about 1,200 pounds. What sets them apart from most sharks is their ability to keep their bodies warmer than the surrounding water, a trait called endothermy. This gives them a turbo boost for speed and stamina but comes with a catch: they need oxygen-rich water to fuel their high-octane lifestyle.
The method used by the study
Byrne’s team used satellite tags to track makos over a decade, following their movements across thousands of miles in the Pacific. What they found was startling: the sharks rarely crossed south of a line around 12 degrees latitude, near the North Equatorial Current. It was as if an invisible barrier was holding them back. After diving into the data, the researchers pinpointed the culprit—a massive region of cold, oxygen-poor water called the Pacific oxygen minimum zone, the largest of its kind in the world.
This zone acts like a trap for makos. In the eastern Pacific, ocean currents push this low-oxygen water closer to the surface, creating a phenomenon called “habitat compression.” The sharks get squeezed into a thin layer of warm, oxygen-rich water near the surface. But here’s the problem: that surface water can get too toasty for makos, risking overheating, while the oxygen-starved depths below are off-limits. “It’s like they’re caught between a rock and a hard place,” Byrne explained. “Too warm up top, not enough oxygen down below.”
The Atlantic Makos
To confirm their theory, the team compared Pacific makos with their cousins in the west Atlantic, where oxygen minimum zones aren’t as restrictive. Atlantic makos could dive deeper into cooler waters without hitting an oxygen wall, giving them more room to roam. In the Pacific, though, makos were stuck, spending less time at the surface as temperatures rose but unable to dive deep due to low oxygen. The result? A natural boundary that’s shrinking their playground.
Makos under pressure
This discovery is a big deal for mako sharks, already under pressure from overfishing and habitat loss. These apex predators play a key role in keeping ocean ecosystems balanced, but their slow reproductive rates make them vulnerable to population declines. Adding to the challenge, oxygen minimum zones are expanding as climate change reshapes ocean conditions, potentially boxing makos into even tighter corners.
Byrne’s findings highlight how the ocean’s invisible forces—like oxygen levels and currents—shape the lives of its wild inhabitants in ways we’re only beginning to understand. “These boundaries aren’t something you can see from a boat,” Byrne said. “But for mako sharks, they’re as real as a brick wall.”
As conservationists rally to protect these high-speed hunters, studies like this are a wake-up call. With their numbers dwindling, makos need all the help they can get. So, the next time you hear about a mako shark’s jaw-dropping speed or acrobatic leaps, remember: even the ocean’s fastest fish can’t outrun the challenges of a changing world.
