From the telegraph wires laid across the Atlantic in the 1860s to the fibre optic wires carrying digital data today, our oceans are criss-crossed with lines used for 98% of our communication (pdf). But when technology is superseded or a company ceases to trade, what happens to the cables and their copper, aluminium, steel and plastic?

Some companies upgrade the cable to make it fit for purpose, others can reuse it (and its accompanying repeater devices, which help transmit signals). It can also be recycled into raw material for industry.

Despite this, Arne de Jong, a Dutch ship captain who co-founded cable recovery company CRS Holland, estimates 94% of unused cables and 72,000 repeaters are abandoned on the seabed, containing materials worth billions of dollars. CRS Holland has been shortlisted for a Dell Circular Economy People’s Choice Award for addressing this deep-sea challenge.

“It is like the Wild West in the middle of the ocean,” says de Jong. “There’s no police or authority that can control it. There are millions of kilometres of cables on that ocean floor.”

De Jong believes this cable is a precious resource that can yield valuable materials for re-use. Since 2009 his vessel has reeled in almost 20,000km of defunct cable, worth – he reckons – some $270m (£213m).

CRS isn’t the only one to realise the value of this cable – sometimes pristine and worth almost as much as new. From France-based Orange Marine to South African Mertech Marine, a host of other firms are similarly busy, not least to help meet demand from developing countries that can’t necessarily afford new cabling.

Nicole Starosielski, author of The Undersea Network, points out that pulling up old cables can be costly, particularly if newer ones are damaged in the process. However, she agrees that reusing older cables can be a tremendous asset, particularly in places where it wouldn’t be economically feasible to lay a new system.

Any state can lay submarine cables on the international waters under the United Nations convention on the law of the sea. While current cable operators have licences, nobody is apparently responsible – for example – for defunct telegraph cables from long-gone companies.

Peter Jamieson, chairman of the European Subsea Cables Association, an association of cable owners, operators and suppliers, says decommissioned cables are dealt with on a case by case basis, depending on issues including licence conditions in territorial waters, environmental impact of removal and whether they can be reused. “Any cables not recovered remain the liability of the cable owner,” he adds.

Recovering and recycling cables lying in deep water, often outside national jurisdiction where most cable recovery takes place, does not have a significant impact on the environment, according to Keith Schofield, general manager of non-profit industry body the International Cable Protection Committee. In contrast, he says, the peer-reviewed evidence suggests it is environmentally best not to disturb the seabed in shallow water.

Brian Bett, a deep-sea biologist from the National Oceanography Centre, adds that cables probably make little difference to deep ocean life. “They have a tiny to zero impact,” he says. “But there could be a carbon footprint assessment of the diesel fuel used to recover them.”