In southern New England, water temperatures have gotten uncomfortably warm and the lobster fishery has collapsed. A little to the north, in the Gulf of Maine, temperatures have hit a sweet spot for lobsters and landings have exploded.

That has been a boon for Maine lobstermen, but for some who live and fish near the Canadian border, it has also brought heightened tensions with their neighbors — and competitors — to the north. This tension is the focus of reporter David Abel's new film, "Lobster War."

The conflict is becoming obvious on tiny Machias Seal Island, situated in waters known by both countries as “the grey zone.”

“The Canadians, in the 1800s, decided to build this light house as a way of asserting their sovereignty,” Abel told Living Lab Radio. “That lighthouse is now the only manned lighthouse in all of Atlantic Canada.”

Abel has won awards covering fisheries and environmental issues for The Boston Globe. He previously co-directed and produced "Sacred Cod," a film about the collapse of New England’s cod.

“Nobody really cared that much about this island for centuries, but they cared about the waters around them,” Abel said.

In the last decade, as the Gulf of Maine has warmed, it has reached the perfect temperature for lobsters. The population has surged, with the catch hitting some of the best years on record.

At the same time, waters in southern New England and New York have gotten too warm for lobsters and the population there has plummeted.

The worst-hit areas are south of Cape Cod, including the Long Island Sound, where the lobster catch has dropped by 90 percent. But even places as far north as Portland, Maine, have seen more modest lobster catches in recent years.

The richest lobster fishing grounds are now near Machias Seal Island, creating an early example of conflict caused by climate change.

“There have certainly been threats back and forth and there has been some sabotage of lobster traps on both sides of the border,” Abel said.

“One of the fishermen was recounting a story to me about how some of his fellow fishermen had brought guns to sea to try to scare off some of their counterparts from across the border. And then at the end of the story he said, ‘Well some of those fishermen could have included me.’ So, it is not hypothetical.”

Screenings of the film are coming up. You can see that list here.