Monitoring shows little long-lasting effect from Rena
3 December 2013
Monitoring shows little long-lasting effect from Rena grounding
A comprehensive monitoring report into the effects of oil pollution from the grounding of the MV Rena on Astrolabe Reef in 2011 shows few long-lasting impacts on Bay of Plenty maritime habitats.
However the environment has not yet returned to its ‘pre-Rena state’, the report says. The 460 page report (plus 243 pages of appendices), which covers the first two years of ongoing survey and research work, details one of the most comprehensive, multi-disciplinary studies ever undertaken in response to a marine pollution incident.
University of Waikato Chair in Coastal Science Professor Chris Battershill said initial concerns that oil would have a long-lasting and negative impact on beaches and fisheries could mostly be put to rest. The monitoring is part of the Government’s $2.4 million Rena Long Term Environmental Recovery Plan.
“While there is still some evidence from time to time of heightened Rena-sourced contaminant levels in kaimoana species on some of the beaches, and northern parts of Motiti, the vast majority of kaimoana and other species have survived, and no evidence has been found of any catastrophic die-off,” he said.
He said the report covered the immediate and medium-term environmental response to the incident, and did not aim to give a comprehensive assessment of the long-term environmental effects, or provide a complete assessment of “the myriad complex interactions” surrounding the Rena grounding. These assessments would be planned over the coming months, on top of ongoing postgraduate research work initiated by the first phase of monitoring.
“It will be prudent to continue to monitor key locations affected by tar balls and other debris over the next year to pick up any longer-term trends. We also want to assess what impact the re-exposure to pollutants is having on kaimoana and other species.”
In other findings based on laboratory studies done within the project, the impact of heavy fuel oil and the dispersant Corexit on juvenile finfish such as kingfish and flounder, showed effects at higher exposures. However as the dispersant was used only briefly on the oil spill at sea, and given the strong offshore wind conditions at the time, there were no environmental effects, he said. There is now little evidence of remaining oil or tar balls around the Bay of Plenty’s coast, and oil washed up on rocky reefs has largely disappeared.
“Very little oil residue has been found in coastal beach sediment cores, which sample deeper down into the beach sands. However, some oil and other debris from the shipwreck and containers continue to wash ashore during storms.”
By world standards, the oil spill resulting from the Rena grounding was relatively minor in terms of the volume of oil lost at sea. But by the same standards New Zealand had one of the most pristine coastal environments anywhere, and the grounding was potentially a major maritime disaster for the country, he said.
The report was a snapshot in time, covering
surveys conducted over the two years since the Rena
grounded. Professor Battershill said the survey work was
unique internationally because it had been based on
comprehensive information about what the environment was
like before the ship struck rock, and the philosophy of the
approach was steeped in Matauranga Maori [traditional Maori
Additional information would come from five Cultural Impact Assessments undertaken by iwi, a mauri assessment of the Maketu area and a Matauranga study.
A surf zone survey is currently underway to assess the extent of any subtidal accumulation of old oil and sand composites given some re-emergence of tar balls, and the beach and rocky shore surveys are being repeated.
Otaiti findings (Astrolabe Reef)
Professor Battershill said contamination of sediments and kaimoana at Otaiti near the ship’s hull appeared significant as might be expected from a stricken ship, and a full status report had been commissioned by the Rena owners after a comprehensive survey was completed in August 2013. The owner has worked with the Regional Council, University of Waikato and other agency scientists on the sampling programme, and results are due in the next few months.
A preliminary survey by the University in November 2012 found PAH and metals contamination was restricted to within about 100m either side of the vessel where it lay on the reef slope. There was some evidence of contamination in the localised food chain, but this was based on a very small sampling effort and needed substantiation, Professor Battershill said.
The northern end of Motiti Island was the only offshore rocky reef location showing more consistent exposure to Rena-related contamination. “Levels of PAHs and other contaminants are low, but are raised above background levels,” he said.
“By the end of the survey period, the remainder of Motiti Island appeared to be unaffected, however, given the proximity of Motiti to Otaiti and the fact that there is a resident population, further monitoring is recommended.”
Further work was planned, and the information would be useful nationally and internationally, should other incidents occur in the future, he said.