Animal populations appear to decrease where the deep sea is being mined, and the impact on marine life of the controversial industry may involve a wider “footprint” than previously expected.
According to analysis of seabed ecology undertaken after drilling tests in 2020 in Japan – the country’s first successful extraction of cobalt crusts from deep-sea mountains – there was a decrease in marine life such as fish and shrimp at the site a year later. The density had dropped even further in areas outside the impact zone, by more than half.
Travis Washburn, an ecologist who works with the Geological Survey of Japan and was the lead author of the study, published in Current Biology, said the findings had “large implications” for decision-makers negotiating regulations on proposals for deep-sea mining.
“We may need to broaden what we think of in terms of what deep-sea mining impacts are,” said Washburn, whose work focuses on the benthic zone – the lowest region of a body of water. “There are large implications if we are currently treating some sites as unimpacted or controls when they are in fact changing from indirect mining impacts.”
The team of scientists analysed data from visits by Japanese mining engineers to the Takuyo-Daigo seamount. A year after the test extraction, researchers observed a 43% drop in fish and shrimp density in the “deposition” areas directly affected by sediment pollution, and a 56% drop in surrounding areas.
“It is easy to assume that once you are outside the zone of deposition there will be no impacts from mining,” said Washburn. “However, if some animals leave the periphery of the deposition area, this would extend the total area of impact.”
Washburn warned against the rush to mine the seabed, and said it could be decades before the full impact on marine life would be known.
The International Seabed Authority and its 168 members have yet to agree regulations governing the industry. The 9 July deadline for the quasi-UN body to adopt regulations or consider applications for mining contracts under existing laws came and went last Sunday, meaning commercial deep-sea mining could proceed without new rules.
Washburn urged decision-makers: “Use all the data we currently have out there. There is still so much we don’t know, but it will likely be decades to answer some of those questions.”
