A lobby group for the deepwater fishing industry says plans to mine seabed near the Chatham Islands will amount to wholesale environmental destruction.

Chatham Rock Phosphate has been given a 20-year permit to mine 820 square kilometres of seabed on the Chatham Rise.
A catch of hoki hauled into a ship in the Chatham Rise area.

A catch of hoki hauled into a ship in the Chatham Rise area.

It's the first permit granted by New Zealand Petroleum and Minerals under the amended Crown Minerals Act that came into force earlier this year.

Deep Water Group chief executive George Clement says the area in question is a significant nursery area for juvenile hoki.

"Given what we understand is being proposed as a mining method," he says, "which is to suck up between 20 centimetres and one metre of the seabed, bring it to the surface, kill everything in it and then disperse the tailings over a wide area, we just think that that's folly."

However, Chatham Rock Phosphate's chief executive, Chris Castle, says the mining operation will only affect a very small area of the nursery area.

Mr Clement says his group will oppose the plans through the marine consent and consultation process, which takes into account the environmental impact of the project.