By SIMON COLLINS science reporter
Scientists have raised the alarm about fishing trawlers that are destroying deepwater coral around New Zealand as far south as Fiordland.
The trawlers, fishing for deepwater species such as oreo and orange roughy, drag nets along the seafloor using heavy cylinders designed to ride over uneven ground.
As well as fish, they are catching "trees" of fragile coral that sometimes grow 5m to 10m high - up to 2km under the sea.
Some scientists and environmentalists want the Government to ban trawling on more underwater "seamounts" where the coral grow. Nineteen of the 800 known seamounts in New Zealand's exclusive economic zone were protected from trawling two years ago.
Dr Steve O'Shea, a squid and octopus specialist who quit his job with the National Institute of Water and Atmospheric Research (Niwa) in January to speak out on marine policies, said trawlers had scooped up hundreds of thousands of tonnes of coral from seamounts in the past 25 years.
" They are wiping it out. It's been going on since 1979."
He said 105 different species of coral had been identified so far in New Zealand waters from the Far North to south of the South Island. More were found last month in a joint New Zealand and Australian expedition around Norfolk Island.
Unlike tropical coral, deepwater coral species usually live below human diving depths, although they are found in shallower waters in shady places such as under the arches in the Poor Knights Islands and inside the fiords of Fiordland.
Since they grow typically at only 1.5mm a year and live for 400 to 500 years, they may take many centuries to recover from trawler damage.
In his book Deep New Zealand, Otago University marine biologist Peter Batson wrote: "Anecdotal accounts of fishing virgin seamounts tell of trawl nets filled with coral trees, and of repeated hauls over the same seamount yielding progressively fewer and fewer coral fragments.
"Though we may never know, it is quite possible that undiscovered species have become extinct in the last two decades through deepwater fishing, without our ever encountering them."
A Niwa report in 1999 said six trawls on previously unfished seamounts caught 3000kg of coral.
In contrast, 13 trawls on seamounts in areas which had been fished on the northwest Chatham Rise, east of the South Island, caught only 5kg of coral.
"These animals grow very slowly. We know they are very fragile, and we have a pretty good idea of the way things look," said Mr Batson.
"Aside from the corals is a host of invertebrate species that rely on the coral in order to survive, so when the coral goes, so do some of the other invertebrates. There are a number of crustaceans and things that are physically growing on the coral."
Another Otago marine biologist, Dr Keith Probert, said that despite their great depth, the deepwater corals supported "a huge diversity of associated organisms" that made them "like a rainforest" in ecological terms.
He said the 19 seamounts that were protected in 2001 "doesn't sound like a huge number when you consider the size of the New Zealand exclusive economic zone".
A senior policy analyst for the Ministry of Fisheries, Stuart Brodie, said the ministry was looking at options for further protection of the seamounts.
"While we have been looking at what further action is required, nothing definite has been developed, but we are undertaking an ongoing review of this issue," he said.
"Part of the equation is to provide the right incentives for the industry to modify their own behaviour."
The ministry aimed to create a framework of standards that could identify where fishing was sustainable and the environmental impact minimised.
"So we are trying to create the right incentives, but to build up the information takes time and cost. In the meantime you still want a viable fishing industry."
* Dr O'Shea will speak on giant squid, in lecture theatre AA236 at Auckland University of Technology on June 10 at 5pm.
On the web: Oceans
Coral structures are built by tiny animals whose shells remain after the animals have died.
Deep-sea corals grow on continental margins, in canyons and on seamounts, generally between 250m and 1500m below sea level.
Deep-sea coral animals build extremely slowly but live for hundreds of years.
Deep-sea black coral "trees" grow up to 5m high and some "bubblegum" coral structures can be up to 10m high.
The coral structures are extremely fragile and easily damaged by trawlers.
Herald Feature: Conservation and Environment
By SIMON COLLINS science reporter