Deep Blue 1 with a new tower retrofitted to the cage. Credit: Rizhao Wanzefeng

China’s largest offshore salmon pen back at sea with significant modifications

A newly modified Deep Blue 1 -- China's largest offshore salmon farm -- has been towed back to sea following "regular maintenance", which includes the retrofitting of a large 35-meter tower.

In an announcement on Thursday, Rizhao Wanzefeng Fisheries -- the Chinese firm behind the project -- said it towed the modified pen 130 nautical miles from the Chinese coast to a location in the Yellow Sea.

Some 130,000 fish smolt were then transferred to the pen, the firm said.

A spokesman for the firm told Undercurrent News half the transferred smolt were rainbow trout, half were Atlantic salmon.

In a short video, the huge, modified pen is seen towed by tugs. A tower -- which the spokesman confirmed is 35m in height -- is fixed atop the pen (see feature photo and gif below).

Previously, the pen did not have a tower.

Deep Blue 1, the world's second-largest offshore pen used to farm salmon after SalMar's Ocean Farm 1 in Norway, was designed and built by Chinese state-owned shipbuilding company Qingdao Wuchuan Shipbuilding and launched in May last year. In July, the pen was towed 130 nautical miles to the Yellow Sea and stocked with 200,000 smolt, Wanzefeng said.

Earlier this year the 35m-tall, 60m-wide pen was returned to a port in Weihai, Shandong province, less than a year after its launch, where it underwent "regular maintenance", a spokesperson told Undercurrent at the time. The salmon were also removed.

The spokesperson said following the modification the pen would be situated at a new location in deeper water, "very near to the original site".

"If you look at the cage -- which is around 35m in height -- what they've put on top looks similar to that," a source, who did not wish to be quoted by name, told Undercurrent. "If you add 35m, it's going to be installed somewhere different, where the water is 60-70m deep. Otherwise, the top still will stick out," said the source, noting the pen is designed to sit on the seabed.

Wanzefeng's pen submerged in the Yellow Sea. Credit: Wanzefeng

Wanzefeng said the deeper water would be colder than water at the surface, and therefore more suitable for raising salmon.

"They [Wanzefeng] said that they're aiming to farm some 50m deep; the pen will be standing in 60m or 70m water, and the top of the cage would be at 40m, and the middle of the cage at about 50m," said the source.

Complications harvesting?

The spokesperson said Wanzefeng would adapt its harvesting method following the redesign; because it will sit deeper in the water the pen will need to be raised from the seabed in order to harvest the fish.

"It will take about 24 hours. We would raise the pen only in good weather," he told Undercurrent. He said it would use a vacuum fish pump to capture the fish in a method similar to the reverse of transferring the salmon smolt to the pen (see picture below).  

A vacuum fish pump is used to transfer salmon smolt from a barge to Deep Blue 1. Credit: Wanzefeng

The spokesman said the modifications -- including transporting the pen back and forth to the installed locations -- cost in the region of $4 million-$5m.  

The first source said the redesign could pose challenges to its operation, however; retrofitting the tower -- which could weigh 300-350 metric tons by his estimates -- to the pen could cause structural stress. "As soon as you start submerging the pen, that's when this thing becomes very unstable."

He said raising a pen of Deep Blue 1's size to harvest might be impractical. "It's not something you want to have to do on a regular basis."

The spokesperson did not contend that these could be issues when they were put to him by Undercurrent.


A project led by state-owned enterprises and China Ocean University, Deep Blue 1 has been shrouded in secrecy, a second industry source in China told Undercurrent. "They're not very open, so it's really hard to get exact information about this project," he said.

However, the spokesperson said the project is "no secret"; for instance, he explained the smolt comes from three different sources.

"We produce some of the smolt ourselves; some we get from farmers in mountainous regions, we give them the fingerlings to raise and they farm to the correct sizes; and some we get from third-party companies."

Shandong Oriental Ocean Sci-Tech, the first company in China to establish a land-based salmon hatchery and smolt facility, told Undercurrent it did not supply Wanzefeng any smolt.

Wanzefeng is known to operate a smolt facility in Shandong; in November 2018, the firm was fined CNY 200,000 ($29,102) by local authorities in Rizhao city because its hatchery and smolt facility broke environmental laws.

The spokesperson said the success of the project should be judged early next year when the salmon and trout are expected to reach harvest size.

Deep Blue 1 on the water surface in the Yellow Sea. Credit: Rizhao Wanzefeng

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