The federal government is investigating reports that two Canadian fishing vessels were approached, and crew members questioned, by U.S. Border Patrol agents in Canadian waters in the Gulf of Maine in late June.

According to Global Affairs Canada, the incidents occurred June 24 and 25 around Machias Seal Island and North Rock.

While details are scant, the fishermen are members of the Grand Manan Fishermen's Association. Laurence Cook, the association's chair, wrote on Facebook that the U.S. officials claimed they were "looking for illegal immigrants."

On Wednesday, Cook said further that border officials have stopped at least 10 fishing boats in the past two weeks. CBC News has only been able to confirm two of those instances with Global Affairs, but has requested information about any other investigations as well.

Decades of dispute

Machias Seal Island is a tiny spot between New Brunswick and Maine that has been the subject of a territorial dispute between Canada and the United States for decades.

Roughly 700 square kilometres of water surround the island in what's called a grey zone. Lobstermen from both sides of the border fish those waters.

In 1984, Canada and the U.S. sent their competing boundary claims in the Gulf of Maine to the International Court in The Hague, but excluded the island from their arguments.

There have been discussions between the two countries since on how to sort out the dispute, but so far there has been no agreement.

Regular exercise?

In a statement on Wednesday, the association said its understanding of the situation now is that it was part of a "regular exercise being conducted along the U.S. marine border."

Melanie Sonnenberg, program manager with the association, said in an email that the association has fishermen who were approached last week and the week prior, and the association was not aware of the exercise at the time.

She said they learned the exercise would last for a couple of weeks and would end June 30.

"They're stopping everybody. It's not exclusive to Canadians," said Sonnenberg.

She said ​63 Canadian lobster boats fish the grey zone, though none fish there exclusively. She believes a similar number of American boats fish the same zone.

The statement from the association said they are working with Ottawa to ensure their fishermen will be able to continue their fishery in a normal manner.

U.S. officials told CBC News in a statement late Wednesday that the border agents were in the area to "enforce immigration laws and other violations of federal law."

The statement — from U.S. Customs and Border Protection, which oversees the Border Patrol — also noted its agents don't handle fishing or boating violations, which are the purview of the U.S. Coast Guard.

Global Affairs Canada confirmed it is investigating the incidents and said it will be contacting U.S. agencies involved.

Machias Seal Island is roughly 19 kilometres southwest of Grand Manan and 16 kilometres from the coast of Maine. (CBC)

"Canada's sovereignty over the Machias Seal Island and the surrounding waters is long-standing and has a strong foundation in international law," Global Affairs spokesperson Elizabeth Reid said in an email.

"Until the matter of the boundary is resolved, we will continue to take practical steps with the U.S. to ensure that the area is well managed.

"Canada and the United States have a long history of co-operation which ensures that fishing in this area is well-managed and safe for both countries."

'Concerning to see'

Robert Huebert, an associate professor of political science at the University of Calgary, said it's a troubling sign, especially given the Trump administration's "zero tolerance" policy at the U.S.-Mexico border.

"To my knowledge, we haven't had many issues on this for quite some time, so it is both surprising and I think a little concerning to see this coming forward again," Huebert said.

He said the fishermen were well within their rights and U.S. officials had no jurisdiction to question them.

Huebert expects to see more instances like this along the border. He said there are a handful of ongoing border issues that could escalate.

"Anywhere where the Americans have a boundary, regardless of how well it may be managed for the last five, 10, 20 years, they are to enforce their version of their legislative control to the full extent and that means growing frictions on a whole host of areas possibly," he said.

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