A team of “ghostbusters” is patrolling the waters of the Gulf of Mannar marine park, off the south-east coast of India, in search of an underwater menace.

The marine scientists and support staff from the Suganthi Devadason Marine Research Institute are hunting for lost or abandoned fishing gear, known as ghost nets, which threaten marine life above and beneath the waves.

Ghost nets choke coral reefs, damage marine habitats and entangle fish, marine mammals and seabirds. They are also a danger to boats, catching in vessel propellers.

Lost at sea

Locating and then removing the nets is a major challenge. The Gulf of Mannar marine park covers 560 square kilometres and its shallow coastal waters are dotted with many small islands.

“Through removal of ghost nets, we hope not only to help conserve corals but also to support the small-scale fishermen who depend mainly on the reef-associated fishery resources for their livelihoods,” Edward Patterson, director of the research institute, said.

Fishing gear is often lost during storms or in strong currents, or after becoming entangled with traps set along the seafloor by other fishermen. The nets continue to fish – hence the term “ghost fishing” – for many years afterwards.

Ghost nets know no bounds, as ocean currents can carry them long distances. It is estimated that 95% of nets that wash ashore in Australia come from other countries.

Burgeoning global fishing operations and gear, made with increasingly durable synthetic fibres, have made the problem worse.

As with other marine debris, ocean currents sweep lost or abandoned fishing gear into "convergence" zones, where it mixes with discarded plastics to form floating trash islands such as the Great Pacific Garbage Patch.

Banishing ghost gear

While there are no quick-fix solutions, the United Nations has outlined practical measures aimed at curbing ghost gear, such as educating the fishing industry about the problem and providing incentives for fishermen to report lost equipment and retrieve nets they find at sea.

Establishing collection facilities at each port would help fishermen to dispose of old, damaged or retrieved gear quickly and safely, ready for recycling.

Technology is also helping with the tracking and recovery of lost equipment. Transponders can be fitted to fishing gear and GPS used to mark the precise spot where it has been lost.

Ocean-floor imaging helps vessels avoid undersea snags, while state-of-the-art meteorological monitoring equipment means they can steer clear of rough seas.

There are also innovative solutions such as biodegradable fish traps which incorporate an “escape hatch” that dissolves when left in water too long.

With as much as 800,000 tonnes of fishing gear left in the world’s oceans each year, action can’t come soon enough.

Organizations such as the SDMRI are working hard to banish ghost nets from local waters, and at a worldwide level the Global Ghost Gear Initiative is bringing together governments, private sector corporations, the fishing industry, NGOs and academia to address the problem.