Manslaughter charges should be brought against the skipper of a boat that took an American couple to the Great Barrier Reef and allegedly left them there, the lawyer for the Cairns Coroners Court said on Friday.

John Bailey, a lawyer assisting the coroner conducting an inquest into the death of Thomas and Eileen Lonergan, said Geoff (Jack) Nairn, managing director of the Outer Edge dive company, breached an obligation to ensure the couple's safety.Lonergan, 33, and his 28-year-old wife, of Baton Rouge, La., were last seen on Jan. 25 diving from the Outer Edge at St. Crispin Reef, 45 miles northeast of Port Douglas.

They weren't reported to police as missing for about 50 hours.

At a preliminary inquest in July, a coroner found that the couple were left behind and drowned.

Rob Davis, a lawyer for the couple's family, said in closing comments that although the performance of other Outer Edge staff members had been sloppy, Nairn must bear the responsibility for what happened.

Despite "a litany of clues" that the couple had been left behind, Nairn failed to instigate a search for them after the boat returned to shore, Davis said.

"I suggest there is no mystery in the fate of the Lonergans," Davis said. "They were left at sea while participating in a normal dive. The only mystery is the staff (of a dive boat) did not ensure that they were back on board and did not report their disappearance for two days."

Nairn's lawyer, Graham Houston, told the inquest there had been no callousness or recklessness and criminal charges were not justified.

Coroner Noel Nunan said he would announce on Oct. 9 whether he will recommend that police charge Nairn with manslaughter.