Oil contamination seen at beaches near a stranded cargo vessel off the New Zealand coast is likely older oil, an emergency official said. The MV Rena, a Greek-company cargo vessel, is sinking off the northern coast of New Zealand. Maritime New Zealand, the agency responding to the disaster, said last week a 6-mile sheen was seen coming from the vessel though rough seas in the Bay of Plenty broke up much of the sheen. Rena struck a reef in the Bay of Plenty in October, dumping around 2,000 barrels of oil into the sea. MNZ managed to get most of the rest of the oil out of the stricken vessel by December. Rob Service, on-scene commander for MNZ, said oil cleanup continued Monday at two areas near the vessel. \"In both cases the oil being collected is predominantly old oil that has been exposed as a result of sand erosion, rather than fresh oil from the Rena breaking in two last week,\" he said in a statement. MNZ workers have deployed a containment boom as a precaution, though no new oil was seen leaking into area estuaries. Service said calmer seas expected this week would give divers the opportunity to survey Rena and plan next steps in the salvage operation.