On the shores of the East China Sea, a team of marine scientists and engineers are working on a new type of aquaculture: offshore marine ranching, without the nets. Rather than physical barriers, the fish are contained by invisible walls of sound.
In April this year, 30,000 juvenile yellow croaker were released into a bay off Luxi Island, part of the city of Wenzhou. Today, they swim free there, in over 100,000 square metres of water. But not entirely free: the bay is enclosed on three sides and on the side open to the ocean there are ten buoys, emitting sound at a frequency which the yellow croaker avoid – a sonic barrier. The fish keep their distance and so even without nets, they stay put in the bay.
It’s not new technology – in America’s Great Lakes it’s used to deter the Asian carp, an invasive species. Some nuclear power stations in the UK are also trying it to keep fish out of water intake pipes.
Now Shi Fuming, founder of Yellow Croaker Island Fisheries, is testing it out for use in marine ranching. He’s no aquaculture expert. He’s a businessman with a three-decade background in electrical automation. On returning home to Wenzhou, he spotted opportunities in aquaculture and, in 2015, founded a firm raising yellow croaker in deep-sea marine ranches.
According to the Wenzhou government’s website, traditional net cages are vulnerable to typhoons. Also, cages also tend to contain fish in high densities, meaning higher rates of mortality. Shi Fuming, hoping to solve those problems in his own yellow croaker farms, reached out to teams from the Chinese Academy of Sciences’ Institute of Acoustics and elsewhere.
The testing grounds let the yellow croaker live more as they do in the wild and help prevent genetic degradation. “Netless aquaculture is more akin to the wild environment and so would better prepare the yellow croaker for life in the wild – this could be key technology for restoring wild populations,” said Professor Yan Xiaojun of Zhejiang Ocean University speaking to the People’s Daily.
Of 30,000 juvenile yellow croaker released by Yan’s team, 3,000 were tagged so their behaviour and escape and survival rates could be tracked. That will allow an assessment of the technology’s ecological value and feasibility. The research could also provide important data for efforts to release captive-bred yellow croaker into the wild to boost population numbers.