Exclusive: Department of Conservation report warns coral at threat from bottom trawling

It's as crucial as it is colourful. Coral is an ecological wonder that is home to thousands of species, but it's under threat. 

The importance of coral cannot be overstated, Greenpeace's Ellie Hooper told Newshub. 

"They underpin the health of the entire ocean ecosystem, they are relied on by many other ocean creatures and also these ecosystems take hundreds of years to grow, " Hooper said. 

But it's under threat from fishing companies accidentally dredging it up while bottom trawling.

A just-released report from the Department of Conservation shows the biggest problem area lies in the northeast Chatham rise area, where 93 tonnes of coral alone has been dredged up, typically during bottom trawls targeting orange roughy. 

"The report confirms what we already know, which is that bottom trawling is a hugely destructive fishing method that has an awful impact on the marine environment," Hooper said. 

On its website, Seafood New Zealand claims companies trawl in featureless areas meaning their nets don't catch coral and disturbance is minimal. 

But Hooper is sceptical. 

"You're not going to be dragging up almost 190 tonnes of coral if you're simply bottom trawling on muddy and sediment seafloor," she said. 

Seafood New Zealand boss Dr Jeremy Helson wasn't available for an interview, but told Newshub in the small amount of seafloor trawled - about 2 percent a year - the majority of this is sand and mud. 

Helson said a better method is needed to measure coral bycatch more accurately and identify dead coral. 

He added, because fishers must return coral to the sea, coral rubble could effectively be measured twice. 

The report itself states, aside from the Chatham Rise, the risk of coral catch appears relatively low, but environmentalists don't buy it.

"This is simply observed coral catch, so we don't have 100 percent observers on New Zealand boats - far from it. And in this period there were close to 30 percent observers on deep-sea bottom trawling vessels," Hooper said.

Meanwhile, Fisheries New Zealand told Newshub some of the seafloor is already protected. 

"About 30 percent of New Zealand's EEZ (exclusive economic zone) is closed to bottom trawling. So there's quite a lot of controls around what fishing can take place where and when," Fisheries management director Emma Taylor said. 

While Taylor said Fisheries New Zealand isn't committing to banning bottom trawling, changes may be on the horizon.

"They might include, for example, some additional restrictions under the Fisheries Act around where fishing could take place and where it would be banned," she said. 

Changes that could help protect coral.