Military battles have been fought over fishing rights, and while it might seem like a silly thing to wage war over, fish are critical to livelihoods around the world.

Maritime laws have been crafted to reduce the possibility of conflict and give countries a fair share of the world’s fish stocks.

But now climate change is threatening to undermine these rules. As oceans heat up, fish species are leaving their normal boundaries and rendering marine jurisdictions irrelevant in the process, according to the Washington Post.

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In fact, fish are on average shifting their territories by 43 miles per decade, according to a report published Thursday in the journal Science.

“It’s like trying to raise cattle when you’ve taken down all the fences,” Karrigan Börk, a professor at University of the Pacific McGeorge School of Law whose background includes a PhD in ecology, told the Post. “Except you can’t even brand the fish. There’s no way to know which fish is yours.”

By 2050, dozens of countries are expected to see new fisheries, according to National Geographic. And unless coastal countries begin to revise international laws, violent disputes could become far more common.

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“[Skirmishes are] already rampant,” Jessica Spijkers, a co-author of the report, told Nat Geo. “It's been brewing under the surface. People have died at sea because fishing boats are out where other boat operators didn't think they should be."

These concerns are being compounded by the fact that up to 90% of the world’s fisheries are being overfished and massive industrial fishing vessels are stripping many fisheries bare.

The authors of the new study looked at 892 species of commonly caught fish and 261 areas where specific countries have control of the waters.

They then factored in climate models, migration patterns, and other factors to create a map of fish trajectories. The team learned that travel patterns are accelerating and this threatens food security, jobs, and economic security for a variety of countries, according to the Post.

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For example, certain schools of mackerel have traditionally been caught by the UK, Ireland, and Norway, but warming ocean temperatures have pushed the fish farther north, and now Iceland is challenging long-standing norms around who can catch the fish.

Other popular fish like salmon and haddock are also being pushed farther north, disrupting fishing vessels.  

The authors argue that countries’ international cooperation is needed to deal with these changes. The UN has sought to update international laws in recent years, but more action will need to be taken on the national level to prevent countries from fighting over fish.

Global Citizen campaigns to protect the world’s oceans and you can take action on this issue here.