Dwayne Matthew Samson of D'Escousse, N.S., was originally charged with second-degree murder in the death of 43-year-old Phillip Boudreau on June 1, 2013.
He entered a guilty plea to the lesser charge in Nova Scotia Supreme Court in Port Hawkesbury, where a sentencing hearing is scheduled for two days in August.
Crown prosecutor Shane Russell said he will seek a sentence in the "double digits" for Samson, while defence lawyer Nash Brogan said he will argue for a sentence between seven and nine years.
Samson was one of four people charged in the case.
Samson’s wife Carla, who owns the lobster boat the Twin Maggies, and Craig Landry are both facing a charge of accessory after the fact.
In January, James Landry was given a 14-year prison sentence after a jury found him guilty of manslaughter, although he was charged with second-degree murder. He has filed an appeal of the sentence.
Russell said Landry's manslaughter conviction influenced Samson's case.
"A jury got to hear all of those facts and from the Crown's standpoint, that was the stronger (case) of the two accused," Russell said outside court. "The Crown respects the original jury decision."
Brogan said he will call a psychiatrist during the sentencing hearing as an expert witness.
"The people on this boat, for years they had been subjected to menace, abuse by Mr. Boudreau cutting traps and (making threats) over many years," he said outside court.
"You have to have a psychiatrist to evaluate your client and get an opinion to see if it is or isn't going to affect sentencing."
Samson, who has been living in Halifax on bail, was allowed by the judge to return to his home in D'Escousse until the sentencing hearing.
An agreed statement of facts read in court Tuesday says the Twin Maggies left the wharf in Arichat at about 5 a.m. for a day of lobster fishing when the boat's crew came upon Boudreau's boat on the water.
The document says the crew was in the Mackerel Cove area when they spotted an object and recognized it as Boudreau's 4.3-metre speedboat.
James Landry and Samson had an ongoing suspicion that Boudreau had been interfering with their lobster traps, the statement says.
Landry, who is Samson's father-in-law, used a rifle to shoot at Boudreau's boat four times, hitting him once in the leg, the document says. When he fired the second shot Boudreau tried to get away but his propeller got tangled in rope, causing his boat to sit idle.
Landry then told Samson to turn the Twin Maggies around so he could gaff Boudreau's boat and tow it out to sea. As they towed it, Boudreau cut the bowline, the statement of facts says, before Landry "hollered' to Samson to turn the boat around and run Boudreau over to sink the boat.
With Samson at the wheel, the Twin Maggies rammed Boudreau's boat three times, knocking him into the water. The document says Boudreau managed to grab onto a red gas can and was floating when Landry hooked him with a gaff and Samson drove the Twin Maggies out to sea.
At one point after Boudreau had slipped from the gaff, he escaped from his sweater and began treading water, the statement says. Landry gaffed Boudreau a third time and Samson again drove the Twin Maggies out to sea.
It says when Boudreau was released from the gaff by Landry, he rolled over, face down in the water.
Afterwards, the court document says, the crew of the Twin Maggies resumed fishing.
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