The maximum sentence suspension under Tongan law was three years, which meant the sentences required amendment.
Jonesse's sentence was not suspended but may be after appeal, Mr Kefu said.
The fourth man convicted over the sinking, acting head of the government's marine division, Viliami Tu'ipulotu, received a three-year fully suspended sentence.
The 37-year-old ferry lurched and sank quickly in heavy seas during a night voyage north of the capital Nuku'alofa in August 2009.
The boat had been purchased from Fiji just three months earlier but its poor condition, including large holes and severe corrosion, made many islanders fearful of travelling on it.
Supreme Court Justice Robert Shuster, who presided over the case, said at the end of hearings that he was "horrified" at both the condition of the boat and the lack of information available to passengers about emergency procedures.
However, the judge handed down sentences that many, including Matangi Tonga website editor Pesi Fonua, considered inexplicably light.
"So many people lost their family members and yet we have sentences of just a few years," Mr Fonua told AAP at the time.
- NZPA
