Editor's Note: This article originally appeared on Business Insider.

Fishing fleets that haul in huge catches, sometimes illegally, from around the world are a security challenge that has already caused armed encounters, senior U.S. military officials said this month.

Illegal, unreported, and unregulated fishing, as it's known, exploits countries' inability to regulate their waters and poses an economic and security challenge, the U.S. Coast Guard says in its recent IUU fishing strategic outlook.

“It's bigger than catching a few boats with illegal tuna. This is really about systemic violations of … sovereignty, economic security, weakening of the global rules-base order,” Adm. Karl Schultz, commandant of the Coast Guard, said last week at a think tank event.

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Annual losses from IUU fishing are likely in the tens of billions, according to the outlook. It has an acute effect in places where fish is a major source of food and economic activity, especially in Africa, Latin America, and Oceania.

Many countries engage in IUU fishing, but scrutiny has grown on China, which has the world's largest distant-water fishing fleet and heavily subsidizes it.

“In the '70s, '80s, the Chinese fished out their own domestic waters and then started looking further,” Philip Chou, senior adviser at Oceana, a nonprofit ocean conservation group, told Insider.

Those Chinese ships supply domestic and international markets, Chou said. “Increasingly now the expansion has to do with the investments that these businesses in China have in the global seafood trade, which they're finding pretty lucrative.”

73,058 hours of fishing

Dismay with Chinese distant-water fishing was piqued this summer, when more than 300 fishing boats, many Chinese-flagged, gathered near Ecuador in the fragile environment around the Galapagos Islands.

The boats arrived in July and left this week, but Oceana found that between July 13 and August 13, nearly 300 of them spent 73,058 hours fishing, mainly for squid, just outside Ecuador's exclusive economic zone.

The intensity of that fishing raises concern about the fleet's impact globally, Oceana said in its report. Their actions also broke China's own rules for sustainable fishing.

Related: Hundreds of Chinese fishing boats lurking off South America add to fears about a future war for fish

“Daily, for periods of in excess of eight hours, a significant portion of this fleet turns off their Automated Information Systems,” Navy Adm. Craig Faller, head of U.S. Southern Command, said at the event, referring to an automated ship-tracking system.

“As a mariner with decades of experience, I can tell you the only time that that happens in that kind of frequency and that length is to cover up illegal activity,” Faller said.

Oceana found 43 cases over that month-long period in which Chinese fishing boats appeared to turn off their AIS transponders, with an average gap of two days. That can be a sign of illegal fishing or that boats are transferring their catch to refrigerated carrier ships, Chou said.

Those carrier ships can mix legally and illegally caught fish, “and it's very hard to distinguish what's what when that comes into port,” Chou said, adding that carriers allow boats to fish “almost indefinitely.”

'Gone kinetic'

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Many Chinese boats fishing off of Ecuador were and are now fishing elsewhere around South America. Among the region's coastal states, illegal fishing “is in their top three, if not the top, of their list of security concerns,” Faller said.

“It's threatening their livelihoods, and our partners' security — particularly in this neighborhood … with its close proximity — directly affects the homeland security of the United States,” Faller added.

Ecuador jailed a Chinese fishing crew in 2017 after catching them with endangered fish. Argentina has fired on Chinese boats, sinking one in 2016.

Those countries are “fighting that same illegal-fishing fight, and in fact it's gone kinetic in Argentina,” Faller said.

Chinese ships have also been detained and fined around Africa. Despite those consequences, “for ultimately who is responsible, the owners, in my mind the repercussions have been limited,” Chou said.

The fish cops

China has the largest distant-water fleet and is implicated in the most offenses, but the EU has “one of the larger distant-water fishing fleets” and often fishes off West Africa, Chou said, citing Taiwan and South Korea as other major distant-water fishers.

Countries do work together to counter illegal fishing. Schultz told Insider in a 2018 interview that the Coast Guard had “a good, functional working relationship” with China; other officials have said the same of Russia.

Multilateral institutions, such as regional fisheries management organizations, have been set up to manage fisheries. But RFMOs “are generally not run well,” Chou said. “There's a lot that gets away under their jurisdiction.”

Countries also try to deter illegal activity with a physical presence. US Coast Guard cutter Bertholf patroled with Ecuador's navy off the Galapagos Islands in August, for example, and this month cutters Kimball and Bear returned from similar operations in Oceania and West Africa, respectively.

“I've got a new fast-response cutter head into Guam today, followed by two additional fast-response cutters. You're going to see more of those vessels in those parts of the world,” Schultz said at the September 17 event. “I think we're going to look at taking some of our law-enforcement attachments [and] potentially repurposing them as fisheries attachments.”

Faller and Schultz linked competition for resources to broader competition with China. Both said increasing the capacity of and coordination with partners was important to that competition.

“This isn't about the Coast Guard being the fish cops across the globe. We don't have that capacity,” Shultz said. “Our ability to share information securely with like-minded partners, it scales up. It scales up from a fishing threat to a counter-narcotics threat to a terror threat to the next global threat.”

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