Joseph James Landry, 67, pleaded not guilty to second-degree murder in the death last year of Philip Boudreau.
A jury found him not guilty on that charge but convicted him of manslaughter after a day of deliberations at the Nova Scotia Supreme Court in Port Hawkesbury.
Crown prosecutor Shane Russell said outside court that Boudreau's family was disappointed the jury didn't convict Landry of the more serious offence.
"They heard a lot of gruesome details about what the Crown presented," Russell said. "To find a verdict of not guilty on second degree murder ... obviously they're upset."
Margaret Rose Boudreau, the victim's sister, declined comment as she left the court.
Earlier this week, the jury viewed a sworn, videotaped statement Landry gave police where he said he intended "to get rid of" Boudreau. Asked by an RCMP investigator what he meant by that, Landry replied, "Kill him or whatever."
Defence lawyer Luke Craggs said the Crown failed to prove Landry intended to kill Boudreau, calling the verdict a victory for his client.
"We can infer from the verdict that the jury said that though maybe he said he wanted to kill him, the actual physical action that caused the death of Philip Boudreau wasn't an intentional act by James Landry," he said.
Landry's wife wiped her eyes crying after the verdict. Landry showed no visible reaction as he heard the jury's decision and was remanded into custody with a sentencing hearing set for Jan. 29.
The 43-year-old Boudreau's body hasn't been found.
Crown attorney Steve Drake told the jury his death was the result of a sustained attack by a three-man lobster fishing crew that included Landry — one of four people charged in the case.
During the trial, Drake said the Twin Maggies rammed Boudreau's boat three times at the mouth of Petit de Grat harbour on June 1, 2013. Prosecutors also said Landry fired four shots from a rifle, one of which hit Boudreau in the leg.
Drake told the court that Boudreau's boat overturned after it was rammed the third time and he was then hooked with a fishing gaff and dragged out to sea before he was tied to an anchor.
Boudreau was last seen by his brother near the Petit de Grat wharf that same day just before 6 a.m.
Boudreau took his red and white speedboat out on the water and it was found overturned without its motor by a local fisherman about one hour later.
Videotaped interviews played during his trial showed Landry initially tell police he shot and rammed Boudreau's boat after the victim cut his lobster traps and threatened to set his house on fire.
At first, Landry maintained his innocence but later changed his story, saying he fired a rifle at Boudreau four times and intended to kill him, adding he took the wheel of the Twin Maggies and ran over his boat.
"I wanted to destroy him,'' says Landry, who accused Boudreau of taunting him for years. "I was seeing black. I was so mad."
He told police he later told the crew of the Twin Maggies he had made a mistake.
"I regret it," he tells an RCMP investigator. "I told you the truth. It's all over now.''
The defence told the jury to discount the videotape, saying Landry was trying to take the blame for what happened to protect others on the Twin Maggies after police told him younger crew members still had their lives ahead of them.
Craig Landry, a deckhand on the Twin Maggies, testified that he did not watch as the Twin Maggies ran over Boudreau's boat three times, though he heard three thuds.
He said Boudreau pleaded for Joseph James Landry to stop firing at him, yelling, "Stop, James! Stop!"
Craig Landry, who is Joseph James Landry's third cousin, was previously charged with second-degree murder but that was withdrawn. He now faces a charge of accessory after the fact.
The captain of the Twin Maggies, Dwayne Matthew Samson of D'Escousse, also faces a second-degree murder charge. His wife Carla Samson, who owns the lobster boat, faces a charge of accessory after the fact. She is also the daughter of Joseph James Landry.
Those three accused have yet to stand trial.