Scientists have just conducted their annual survey of blue whales in the South Taranaki Bight, where Trans Tasman Resources wants to start seabed mining.
This year they documented 68, more than double last year's total of 33.
Dr Leigh Torres gave evidence at the Environmental Protection Authority's hearing into the mining proposal. She was counting the mammals and said seismic surveying is already having an impact.
"Blue whales change their behaviour and get stressed out when there is seismic surveying going on. It's an incredibly loud noise, and so if you add onto that some other low-level background noise, I believe you might push them towards a tipping point. We already are seeing consequences. We see whales out there that look skinny to us, you can see their backbone," says Dr Torres.
Trans Tasman Resources wants the right to extract up to 5 million tonnes of iron sand a year from a 65 square kilometre area of seabed off South Taranaki coast.