Watson, 32, pleaded not guilty to murdering new wife Christina, 26, but guilty to the lesser charge of manslaughter when he fronted the Brisbane Supreme Court this morning.

The pair, who were honeymooning in Australia from the US, had been diving near a shipwreck on the reef, near Townsville, in October 2003 when the new Mrs Watson became distressed and reached for Watson's oxygen mask.

Despite being an experienced diver with a search and rescue qualification, the court heard Watson refused to help her and made no attempt to save her when she began to sink towards the sea bed.

Prosecutors had asked for a five year term, with a minimum of 18 months, but the sentencing judge instead handed Watson a four-and-a-half year head sentence, suspended after he has served 12 months.

He will serve the time in an Australian jail and will be deported immediately upon release.

Twenty-three days he has already spent in custody will be shaved off the sentence as time served.

The court heard Watson had noticed his novice wife, known as Tina, was distressed in the water and had reached for his mask and regulator to get air, but he had not given it to her.

Although he knew she needed assistance and could have grabbed hold of her, Watson instead allowed her to sink to the sea bed.

Prosecutor Brendan Campbell told the court: "It must have been clear to the accused (Watson) if he left her she would most certainly die. It's almost inexplicable he would make the decision to leave her."

The court heard the couple twice refused offers of an "orientation dive" with instructors while on the trip.

"No doubt it was (Tina's) trust in him as her husband that led to her not taking an orientation dive," Mr Campbell said.

"She was unlawfully killed by a man who had married her 10 days earlier."

Watson's barrister Steve Zillman argued his client, who returned voluntarily from the US to answer the charge, had panicked when he saw his wife was in trouble.

Tina Watson's parents, sister and friend travelled from the US to attend proceedings and had all tendered victim impact statements detailing their "devastation" at her death.

Watson was charged at the conclusion of an inquest in Townsville in June last year.

The Coroner, David Glasgow, alleged Watson had held his wife under water, turned the valve off on her air cylinder until she suffocated, switched the air back on, and let her sink to her death.

The inquest heard that on the day she died, they first entered the water at 10am, but Gabe Watson's dive computer malfunctioned, and they returned to the boat.

At 10.37am they went back in, but in minutes, Mrs Watson was dying alone on the seabed, 29 metres below the surface.

Source: Brisbane Times