PORTLAND – The state supreme court has overturned the conviction of a lobsterman accused of attacking another lobsterman with a gaff when a dispute over island fishing rights escalated into violence.

David McMahan was convicted of assault after a melee 20 miles off Maine’s coast in which he wielded the gaff – a large fish hook – and the victim parried with a pitchfork in a dockside battle.

McMahan, who said he acted in self defense, contends he was under siege by other lobster fishermen on Criehaven who felt he was violating their locally imposed rules by using too many lobster traps.

“A bunch of the old boys decided to teach him a lesson, and he stood up to them,” McMahan’s lawyer, Andrews B. Campbell, said Tuesday.

The case, which was sent back to Knox County Superior Court, offers a rare peek into the world of Maine lobstermen, an independent lot who often create their own rules and settle disputes among themselves.

The case ruled upon by the supreme court Monday started with a disagreement between McMahan and others over his fishing practices.

The 10 lobstermen on Criehaven – which is three miles from Matinicus Rock – have an agreement and map showing fishing territories that is recorded in the registry of deeds, Campbell said. Only people who live on the tiny island can fish in the island waters, he said.

McMahan had a home on the island but raised the ire of the others by fishing wherever he pleased and with as many traps as he pleased, Campbell said.

The dispute simmered for several years before it escalated when the victim, Gerald Brown, found an obscene drawing on one of his lobster buoys. Brown immediately suspected McMahan was behind the drawing and confronted him.

“A verbal confrontation ensued with, according to the record, a number of salty, Down East expressions being exchanged,” the Maine Supreme Judicial Court reported in its findings of fact.

The April 1, 1999, confrontation escalated when Brown stepped onto McMahan’s dock, and it ended with Brown being injured and bloodied.

The case ended up in the state’s highest court when McMahan appealed his conviction on an assault charge in Knox County Superior Court.

The state supreme court ruled that McMahan should have been allowed to make a case for allowing some evidence that the judge threw out during the trial. Therefore, the court threw out the conviction.

Campbell said there must be a new trial. But it’s unclear how the prosecution would handle the case since the victim has since died. His death was unrelated to his injuries, the lawyer said.

District Attorney Geoffrey Rushlau said he was not certain that there would be a new trial. Since the trial was heard by a judge without a jury, it’s possible the judge could reopen the evidence, he said. Campbell said the fight was not over the obscene drawing but over the establishment’s attempt to control a “maverick.”

What happened on Criehaven isn’t unique, the lawyer suggested. He said the agreement to parcel out the island fishing grounds and to control the market violates antitrust state and federal laws.

“The same thing that applies to Microsoft applies to everyone else. You can’t allocate markets or fix prices,” he said.