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Bottom-trawling fisheries devastating for NZ’s marine environment, say scientists

Bottom trawler

A bottom trawler in New Zealand coastal waters – “D-day nears”. Photo: Greenpeace NZ

Marine mammals are starving in New Zealand coastal waters. Experts say bottom-trawling needs to be replaced by more sustainable fishing methods or the country risks fishing many species to the brink of extinction.

Pacific Scoop:
Report – By Eva Evguenieva

“Like bulldozing for apples,” is an analogy used by marine biologist Liz Slooten to describe the devastating effect bottom-trawling fishing is having on New Zealand’s marine environment.

“You can walk through the orchard and pick the apples by hand or you can take a bulldozer through and, sure enough, you can probably end up taking the apples out of the orchard but you will completely destroy the orchard,” she says.

Otago University’s Liz Slooten, like other scientists working in this field, is concerned with bottom-trawling fishing and its impact on marine mammals.

Some studies overseas have found reduced fish stocks left due to bottom trawling is causing difficulties for some seal species that have had to change their preferred prey species to poorer food sources to survive, says Slooten.

“These other fish species are not as nutritious so their survival rate and their reproductive rate are suffering because of the change in diet,” she says.

Marine mammals such as sea lions and whales are being affected by the harvesting of their food.

Experts agree the problem is not how much we are fishing; it is the way we are fishing.

Steel bobbins
Bottom trawling fishing uses large steel bobbins, dragged along the bottom of the ocean floor, which are connected to ground ropes and upper ropes.

These bobbins protect the net from being shredded when they are dragged on the sea floor destroying everything in their path.

In squid trawling this not only removes the adults, but also destroys the egg masses, which are crushed by the bobbins.

Other bottom-trawled fish species include New Zealand’s biggest exports – orange roughy and hoki.

Prior to the 1960s, the sperm whales’ diet consisted primarily of orange roughy. Now that this stock is in decline due to large-scale fishing, sperm whales have switched to squid.

But the problem is that – just like the whales – the fishing industry has done the same.

Starving whales
Auckland University marine biologist Steve O’Shea, who has been examining the stomach contents of whales for years, believes that the whales are starving.

O’Shea, director of Earth and Oceanic Sciences, who has studied the stomach contents of more than 400 whales, says: “When we look at the stomach contents of these whales we are finding squid beaks, which cure and collect in the stomachs.

“I can identify, based on a beak morphology, every species of squid because they have different sorts of beaks and I can identify what species of squid those whales have been eating.”

O’Shea says there are 86 species of squid in New Zealand waters. Based on that information, he can determine if a whale ate squid within or outside New Zealand waters and in many cases where it was eaten such as, Antarctic waters.

“What we were finding was that an average sperm whale – a mature sperm whale – needs about tonne of squid or food per day just to sustain its bulk and to get enough water.

“And we were finding that the whales had not eaten anywhere near enough squid or food over the course of their residence in New Zealand waters. The last time they had a jolly good feed was down in Antarctic waters,” says O’Shea.

These whales are migrating from Antarctic waters to New Zealand waters to an area that was once productive with lots of fish and squid.

“The larder is bare and the whales are basically stressed thirsty, malnourished, ulcerated and coming ashore in droves.”

‘Double whammy’
Scientists say endangered seal lions around the Auckland Islands have received a “double whammy” from the arrow squid trawling conducted in the area and their population has suffered a significant decline.

Marine biologist Bob Zuur says: “They definitely catch and drown sea lions – that’s without question”.

“The squid industry also catches a lot of food that the mother of sea lions would also require to maintain their own health and produce milk for their babies, which are on shore.”

The mothers now need to swim further and dive deeper to get the same amount of food than in the past.

“If you combine these together you have a mother sea lion- which is killed –  a pup, which is on the shore waiting for its mother to return and would starve, and the mothers also have fertilised embryos in their wombs which would die.

“The direct result of this fishing could be that by killing one female sea lion, you are effectively killing three. On top of that we don’t know how many of these sea lions are striving or not being able to feed their pups because their food resources have been taken”.

“There are published accounts of sea lions around the Auckland Islands and what we call ‘ribbing’, which means starvation – you see the ribs through the skin of the animal,” says O’Shea.

Alarming decline
There has been a significant and alarming decline in the number of pups that have been born around the Auckland Islands over the last decade.

“There is a significant problem that has not been accepted by the Ministry of Fisheries,” says Zuur.

The industry has developed something called a “sea lion exclusion” device that in theory allows sea lions to escape from trawl nets.

However, there is a limit to the depth and time sea lions can dive and scientists are concerned that by the time they get of the nets it may be too late because, although they may still have enough fight in them to escape, they may not be able to surface in time to take a breath or they may be fatally injured.

The squid industry has a limit to the number of the sea lions they can kill.

“In principle that is not a bad way of doing things, as long as the morals are good. And we have concerns about the morals,” says Zuur.

So this escape mechanism makes it more difficult for the numbers actually killed sea lions to be counted.

Smoke screen
Environment Conservation Organisation spokesperson Barry Weeber says bottom-trawling fishing is by far “the most evasive and broad-scale impacting method used in New Zealand”.

The Ministry of Fisheries has voluntarily closed 30 percent of the waters around New Zealand for bottom trawling.

Weeber says: “This is just a bit of a smokescreen really because of the 30 percent that has been closed. These Baltic protected areas are known in environmental circles as ‘bogus protected areas’.

“They are basically areas that were set aside where very little fishing took place or areas they did not want to fish or that were too deep to fish”.

Another concern is that, although these areas are closed to bottom trawlers they are not closed for other kinds of fishing, of the bottom in the water column and rubbish discarded by the fishing vessels makes its way down to the bottom, altering the seabed communities and perhaps bringing in more scavenging animals.

In an interview for TV3, Ministry of Fisheries acting chief executive John Beaglehole said he believed New Zealand fisheries were in “good shape” and this was because the “quota management system [which] is the basis of how New Zealand manages its fisheries”.

The Ministry of Fisheries also declined to comment when asked if it would consider more sustainable fishing methods such as jigging.

Too late?
Slooten says: “We need to start right now – today. It is a better date to start now rather than tomorrow. The longer we leave it, the worse it will be. It is not quite too late – but it is D-Day,” says Slooten.

O’Shea is not so optimistic.

“It is probably too late. I do think it’s too late.”

Eva Evguenieva is a Postgraduate Diploma in Communication Student on the Asia-Pacific Journalism course at AUT University.

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