A Mongrel Mob member who used a knife to remove his girlfriend's eye has been sentenced to 13 years in prison with minimum non parole period of seven years at the High Court in Napier this morning.

Sio Muliipu, 24, was found guilty of six charges of assault, kidnapping and causing grievous bodily harm after a week-long trial in August.

The Crown had sought preventive detention, however Justice David Collins did not think it was warranted.

Muliipu and his victim, whose name is suppressed, began arguing after Child, Youth and Family would not allow him to live with their infant twins last November.

He assaulted her twice in late November last year.

On December 5 he kidnapped her from a house and held her against her will, assaulting her numerous times and putting a knife into her eye before the armed offenders squad rescued her the next day.

Muliipu denied using a knife as claimed by the woman and said the wound to her eye may have been caused by some toys he had thrown at her during an argument.

The wound caused the woman to go instantly blind in her left eye, which bled profusely, and ultimately had to be removed.

Ophthalmologist Philip Macdonald had told the court earlier that the wound was "almost surgical in nature", about four centimetres deep and probably caused by a small knife. The chances of it being caused by something thrown were "astronomically low".

Muliipu, who has gang tattoos across his face, forehead, neck and arms, denied assaulting the woman on two occasions in late November but admitted kicking and punching her shortly before the eye injury. He said she had lied about the assaults.

Muliipu has an extensive criminal record and had been out of prison for just weeks when he attacked the woman. He was released after telling a judge he wanted to care for his partner and newborn twins.

Muliipu was a key player in the prison riot in Hawke's Bay Prison in June last year while nearing the end of a one-year sentence for assaulting a woman.

The riot, which resulted in an overnight rooftop protest by a handful of prisoners, began after Muliipu was reclassified as maximum security.

He was transferred to Christchurch men's prison and last August pleaded guilty to unlawful assembly in relation to the protest.

He told Judge Jane Farish he and his partner were expecting twins - his first children - the next month and he wanted to get the case dealt with so that he could be out to support her. The children were born on August 28 last year.

He was released in October and assaulted his partner the following month.

Muliipu's brother, Time Muliipu, was found not guilty of being a party to the kidnapping.

- © Fairfax NZ News