The New Zealand Defence Force offshore patrol vessel HMNZS OTAGO has returned to the Devonport Naval Base after almost three weeks of maritime surveillance operations in the Southern Ocean.

Commanding Officer of HMNZS OTAGO, Lieutenant Commander Andrew Sorensen says embarked Fishery Officers from the Ministry for Primary Industries carried out compliance checks on eight licensed fishing vessels.

Extreme conditions were encountered during the NMNZS Otago's patrol of the Southern Ocean. Photos: NZDF

They also monitored for illegal, unreported and unregulated fishing.

'We kept a high operational tempo. As soon as we arrived on station, no time was lost in transiting through first year sea ice, locating and boarding vessels of interest,” says Andrew.

Halfway through the operation, the Navy's offshore patrol vessel was battered by a heavy storm with winds in excess of 80 knots generating 15-metre swells.

'Conditions ranged from blue skies and open water to thick fog, snow and moderate ice conditions.”

The patrol was in support of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), which cooperatively manages the Southern Ocean fisheries and protects the Antarctic marine ecosystem.

The patrol marked the sixth season that New Zealand had conducted maritime surveillance in the Southern Ocean.

HMNZS OTAGO will remain ready to respond to any incidents in the Southern Ocean during the season.

The licensed CCAMLR fishing season in the Ross Sea region south of New Zealand started on December 1 and will continue until the agreed limits are reached sometime in January or early February 2016.