New figures showing the cost of the Rena salvage and clean-up operations has reached $37million emerged during the sentencing of the ship's captain and navigation officer.

The Rena's former master Mauro Balomaga, 44, and navigation officer Leonil Relon, 37, were sentenced to seven months jail on Friday for grounding their ship on Astrolabe Reef.

They plead guilty to a total of 11 charges under the Maritime Transport Act 1994 for operating a vessel in a manner likely to cause danger, under the Resource Management Act 1991 for discharging a contaminant and on three charges under the Crimes Act for altering ship documents.

As the main sentencing charge for Perverting the Course of Justice is a non-violent crime the two men will be eligible for parole after serving half the sentence, and may be returning home to the Philippines in a few months.

Prosecutor for the Crown Rob Ronayne stated during sentencing that as of April 2 this year the Rena grounding, oil spill and aftermath has cost the New Zealand Government $37million.

Most of those costs were incurred in the first six weeks after the Rena struck the reef on October 5, 2011.

Heavy fuel oil began washing ashore from the Rena on October 10. There are four internationally recognised degrees of oiling, heavy, moderate, light and very light.

About 60 kilometres of beaches from Bowentown Heads to Maketu suffered heavy to moderate oiling, with large amounts coming ashore at Papamoa and Mount Maunganui.

The rocky shorelines of Mauao, Moturiki Island and Motuotau Island also had a high degree of oiling.

Oiled wildlife response teams were first deployed on October 8 to remove Little Blue Penguins from their burrows along the coastline.

It was the beginning of the breeding season and most of the next generation was lost as the focus was on saving the adult breeding stock. Un-weaned chicks were left to starve and unhatched eggs were left behind.

By November 7, there were 336 little blue penguins at the Te Maunga Oiled Wildlife Facility in Mount Maunganui.

There were 2299 dead birds collected from Bay of Plenty beaches with 1443 visibly oiled. Those found are estimated to be only a small fraction of total bird deaths.

The crown estimates 350 tonnes of Rena's heavy fuel oil washed ashore. The defence estimate is 180 tonnes.

During sentencing the captain's counsel Paul Mabey QC stated a continuing source of extreme frustration for the captain is Svitzer salvors refusal to act on the advice of the captain and chief engineer when they took control of the ship.

Defence argued the captain and the ship's chief engineer spotted oil in a hold early on, and determined it was leaking into the duct keel from broken piping. They were attempting to shift oil from starboard three to starboard five tanks when the salvors took over the ship.

The salvors started shifting oil from the port tanks as it turns out, says Paul.

'It came from that particular tank that he and the engineer had identified and which they were taking steps to remedy.

'They either would not take the advice or would no listen to him,” says Paul.

'It continues to be a matter of frustration for him. He could have done more to assist if he had been allowed to.”

In addition to the New Zealand government $37million, the Rena has from day one been costing the owner's insurers $US 300,000 each day.