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A tropical fish never seen before off the New Zealand mainland has been discovered at the Poor Knights Islands marine reserve.
The Department of Conservation was using a remote-operated camera when it discovered the small damselfish swimming at about a depth of 80m in the reserve, 24km off Northland's east coast.
Dr Debbie Freeman, scientific office and marine biologist, said the damselfish was a subtropical species normally found in 90-152m depth, and between 26 and 30 degrees latitude south.
Dr Freeman said the Poor Knights was about 35 degrees latitude south, so the fish was a long way south of where it would normally be.
"The damselfish has been found in Australia, the Norfolk Ridge and the Kermadec Islands, but this is the first record of it around mainland New Zealand."
Dr Freeman said the Poor Knights were bathed in a warm water current coming from the tropics, so that was likely the source of this fish.
She did not believe it was anything to do with climate change, although future sea temperature rises could see new species in New Zealand waters.
Dr Freeman said it was possible damselfish had habitated the reserve for some time but had never been spotted as divers rarely went below 40m.
The special high-tech underwater camera was trialled in March and its use earlier this month was the first official survey.
"There was an amazing array of species possibly never seen before. We saw a sea slug that seems to be a new species."
Dr Freeman was operating the video camera, manipulated using joy sticks and a long cable, when the damselfish, about 15cm long, swam into sight. Images sent to Te Papa confirmed its identity.
The camera had been bought about a year ago so the department could monitor the health and diversity of the marine reserves at depths of up to 300m. It could also help map the seabed to better understand and protect marine areas.
Self-propelled, with video and sonar recordings, the camera could even pick up things from the seafloor and bring them back to the surface.
It was next scheduled to be used in the Marlborough Sounds and is being taken to the sub-Antarctic islands in March.
