A World War I-era warhead and a dead blacktip shark attached to a metal hook are just some of the things magnet fishers have retrieved around the U.S. since the hobby spiked in popularity following the advent of the coronavirus pandemic.

The hobby, which involves people throwing powerful magnets into waterways in search of treasure and trash, became an excuse for some to get fresh air and for others to start businesses catering to these hobbyists.

Joshua Dunlap, of northern California, is one such entrepreneur who started Centurion Magnetics in January 2020.

"Little did we know that COVID was starting a few months after [we launched] and it actually kind of worked out perfectly," Dunlap told NPR over the phone. "It became a really popular hobby with people looking for ways to get outside to do something that was different. And magnet fishing happened to be one of those things. It's all over the world, but very specifically, definitely here in the U.S."

But the growth of these small businesses and the popularity of magnet fishing have become murky lately. They're running up against two problems: China's stranglehold on the rare-earth element used to make these magnets and the high demand these materials garner from electric vehicle makers and other green technology companies.

The element attracting all this attention is neodymium, a difficult-to-produce rare-earth metal mostly mined in China, said David Merriman, a research director who leads the rare earth market research at Wood Mackenzie, an energy research consultancy.

"The main growth areas for the use of the [magnets] is within the motors for electric vehicles. So any electric motor, which uses a permanent magnet, and also the generators for, say, wind turbines, as well," Merriman told NPR over the phone from the United Kingdom.

"So as these markets have been really growing quite significantly, there's a huge kind of transition towards green technologies, electric vehicles, renewable energy generation. The demand for these products is increasing quite significantly," he added.

How China developed its grip on neodymium mining

To understand why China has come to dominate the global production of neodymium you have to travel back to the 1980s and 1990s, Merriman said.

At the time, the U.S. and Australia were major producers of these rare-earth elements due to scientists from both countries developing the technology needed to mine these materials, he said. Unlike gold, which can be found in nature as pieces, neodymium is found within different minerals and thus requires a chemical process to "leech out the rare-earths from the mineral structures," Merriman said.

China soon realized that it had substantial rare-earth deposits "that were a byproduct of iron mining," Merriman said.

"It noticed this as an opportunity," he said of China at the time. "And it's because of more lax environmental [and] social regulation within the Chinese industry during that period, it was able to produce material very cheaply. So China started to undercut production of rare earths, within these other regions, running the price down, and basically taking market share globally."

In the decades that have followed, China has continued to out-compete other countries by extending its reach thanks to state backing and state control of mining operations, Merriman said.

"China now dominates the entire supply chain for rare earths and through to the production of rare-earth permanent magnets and high-quality permanent magnet materials," Merriman said.

"So it's been a long play, I suppose, from the Chinese government to take market share, and then extend its market share over different stages of the supply chain, through to the point where it's now a vital part of the supply chain for many kinds of high-technology applications, including some military applications as well," he said.

As of November 2021, China controlled 87% of the global neodymium market, according to a report from MacroPolo, a Paulson Institute think tank based in Chicago.

These magnets have been called "crucial inputs" for electric vehicle motors, MacroPolo added. The element can also be found in smartphones and guided missiles.

The demand for neodymium "is likely to grow at an estimated 18% per annum through 2030," MacroPolo said. This clamor is already being felt by small magnet fishing businesses in the U.S.

There are plenty of metal "fish" but not enough lures

Jose Torres was fed up sitting in his kayak failing to get any bites on his fishing line in southwest Florida.

The fledgling YouTube channel he launched in 2013 to chronicle his best catches was barely getting any attention due to bigger fishing channels with more resources and larger, more exciting, catches caught on video.

Then, last summer, Torres stumbled upon videos of magnet fishing and "it changed my YouTube channel tremendously," he said.

"I have access to thousands of boat ramps, thousands of fishing piers, thousands of sea walls, where pedestrians walk by or where people throw things in the water, accidentally drop things in the water from their boats," Torres said about why he decided to become a magnet fisher.

Torres' YouTube channel has grown from a few hundred subscribers to more than 3,000 today, he said. This has allowed him to monetize his YouTube channel with advertising.

He's also partnered with Centurion Magnetics as an affiliate, giving him a commission from each fishing magnet sale made using his unique code. This partnership was supposed to net Torres significant money but the reality has been anything but, he said.

"A lot of the issues that we were having, that I've experienced, is that my subscribers were sending me emails left and right saying, 'Hey, I've been trying to buy this magnet for the past month, two months, and it's out of stock, it's out of stock; when are you guys gonna get this stuff in stock?' " Torres said.

He said he's lost "hundreds, if not thousands of dollars in revenue from commission sales because of the lack of availability [and] their inability to get these magnets from China. So the industry has taken a big hit."

Keeping magnets stocked is one of the hardest parts of Dunlap's job as CEO of Centurion Magnetics.

The combination of China's control of the neodymium market, the high demand for these magnets and the global supply chain issues plaguing almost every industry due to the pandemic has caused numerous Centurion products to remain out of stock, Dunlap said.

"You know, just honestly staying in stock is still the hardest thing that's hitting us. ... We would keep building momentum and then we went out of stock," he said. "Even if you look on our website now, we're out of stock with an entire line of magnets. We're trying to get them back in stock; it's quite the feat."

Call the bomb squad

While the growth of magnet fishing as a hobby remains uncertain, fishermen like Jake Cowart, of Georgia, find themselves satisfied with the magnets bought at the start of the pandemic.

When COVID-19 shut down the movie business in Georgia, Cowart said his brother Adam — who are both set dressers — was bored and convinced him to try out magnet fishing after spotting a video of someone in the United Kingdom doing it.

The brothers have since pulled up relics dating back to the 1800s, safes, coins and dozens of weapons, Jake Cowart said. In July, Cowart said he fished out a 37mm World War I-era warhead that still had a fuse attached to it.

"I had to call a EOD [Explosive Ordnance Disposal specialist] and bomb squad out to get them to take that thing and defuse it," Cowart told NPR over the phone. "I was scared, to be honest with you, because it's a warhead, and it can explode with any kind of impact. And it was stuck on my magnet on the explosive side. So I was really, really, really freaked out about it."

Cowart has yet to hear about what happened to the bomb after law enforcement officials and EOD specialists came to pick it up, he said.

Cowart and his brother have also pulled up guns that have helped solve cold cases, he said.

"No murders, but they were all gun store robberies and stuff that was stolen from some elder elderly people, you know, that closed some of the cases that were out in Athens, [Ga.]," he said. "It's just something good to get out there for everyone to see, you know that ... we're cleaning up stuff. We don't want to get a bad, bad reputation that people think and we're trying to try to catch all of these people. But ultimately, if they've done something wrong, they need to be caught."

Copyright 2022 NPR. To see more, visit https://www.npr.org.