Iron sand mining could threaten whales and dolphins in the waters off South Taranaki, the Wellington High Court heard today.

The evidence was presented as part of a four-day hearing in an appeal against the Environmental Protection Agency's decision to allow iron sand mining off the South Taranaki coast.

Forest and Bird lawyer Martin Smith said four species - Brydes whales, blue whales, killer whales, and Maui dolphins - are critically endangered.

He said the method used to detect them was inadequate. Over two years there were only 12 flights of between four to six hours to see if marine mammals were present in the water.

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Smith said because they spend most of their time under the water, an aerial survey ran the risk of missing them. He said an acoustic survey, which would monitor the whales calls, would be more accurate.

The EPA has accepted the aerial survey results needed to be treated with caution.

Forest and Bird is just one of six groups appealing the decision to allow the iron sand mining.

- Newstalk ZB