Captain Lin Jianchang is a fisherman born and bred. Sitting on his small trawler mending nets, the 54-year-old says times are tough.

"When I started to fish we could fill our boat completely in an hour, we couldn't move, there were fish everywhere," he says.

"Now there's less fish and it's rare to get a big one."

The world's fisheries are in crisis. The United Nations food and Agriculture Organisation estimates 90 per cent of them are either overfished or at the limit of sustainability, and China is the major player.

By a long way, China has the world's biggest deep sea fishing fleet that strip mines the world's oceans.

The Chinese government heavily subsidises the fleet in an attempt to satisfy the country's insatiable appetite for seafood, which accounts for a third of world consumption.

In the port city of Zhoushan on China's east coast, 500 trawlers raced out to sea on the first day of the season.

Every season is harder than the last. The fleet have to head deeper into the ocean and stay for longer for a decent catch.

The Zhoushan fleet heading out to sea at the beginning of the fishing season. ( ABC News: Steve Wang )

The seas around China have virtually no fish left but the commercial fishing fleet is still huge.

With an estimated 200,000 boats, it accounts for nearly half of the world's fishing activity.

A dozen trawlers returned to Zhoushan with their first catch of the season — crab.

The hauls were good but well under half of previous years.

These days the smaller trawlers and boats mostly catch "trash fish" — tiny fish with little value, used as feed for animals and in aqua farms.

Like most others in Zhoushan, the only thing keeping Captain Lin and his crew afloat are government subsidies.

"The diesel fuel and fixing the boat would cost me 200,000 yuan ($40,000). The government subsidises me more than 100,000 yuan ($20,000)," Captain Lin said.

The Chinese government has given $28 billion in subsidies over the last four years to its fishing fleet.

Subsidies from the Chinese government keep many of the Zhoushan boats running. ( ABC News: Steve Wang )

Chinese super trawlers stripping the ocean bare

Subsidies might keep people in jobs, but overfishing is threatening the entire ecosystem.

Wang Dong, captain of a small trawler, said China's 2,600 super trawlers make it almost impossible to survive.

"The stock of fish is definitely less, the fishnets they have kill everything," Captain Wang said.

"The mega trawlers have bigger engines, so when they pass there's hardly any fish left — big or small."

The government says it is taking action, at least with the smaller fleets it can control closer to home.

The flags wish the Zhoushan fleet a safe and successful trip. ( ABC News: Steve Wang )

Li Wenlong is the general manager of Zhoushan Fishery company and in charge of safety and regulation of the Zhoushan fleet.

"Now we are taking three steps; extending the period of fishing bans, releasing more baby fish and starting to reduce the number of boats to reduce production," Mr Li said.

But Chinese authorities acknowledge on the high seas their super trawlers are difficult to police.

On paper there are tough new laws and punishments but often the super trawlers under-report or do not record their catches.

Many experts say it is too little too late to save the world's fish stocks.

Zhou Wei is the ocean project manager at Greenpeace East Asia.

"We are at crisis point, the world fish stocks are depleted," Ms Zhou said.

"We've lost two-thirds of the large predator fish. Ninety per cent of the world's fish stocks have being fully exploited or are overexploited.

"Our fleets continue to use destructive methods which destroy domestic fisheries."

There are about 500 commercial fishing boats in the Zhoushan fleet. ( ABC News: Steve Wang )

China's super trawlers are targeting the seas in North West Pacific, South America and Western Africa.

Not only are they destroying fish stocks, but they are also wiping out poorer subsistent communities.

Greenpeace East Asia has recently done a study of the super trawler's impact in Western Africa.

"In Western Africa, seven million people rely on fish for income and employment, many more rely on fish for food and animal protein," Ms Zhou said.

"To the local people it's their livelihood but to the industrial fishing fleets it's a business."

Demand is driving the crisis. China's rising wealth means seafood, once considered a delicacy, is now widely consumed.

There is little awareness of sustainability in China's public and conservationists say education campaigns are desperately needed.

Many experts fear if China and other countries do not change their fishing models, there will be very little left for the next generation.

China accounts for a third of the world's consumption of seafood. ( ABC News: Steve Wang )

Editor's note (4/10/18): This article has been edited to clarify FAO data on overfishing.