What Ghost Nets Are Doing to the Reefs We Visit

Two snorkellers swimming beside a sea turtle over a coral reef. Photo: Ocean Calling Retreats.

The first time you see one underwater, it does not look dangerous at all. It hangs over the reef edge, soft and green with algae, moving slowly with the current. Almost pretty. Then you notice what is caught inside it, or the grey, empty patch of reef underneath, and the name starts to make sense. So what do ghost nets do to coral reefs? They scrape and smother coral, they trap animals, and they can keep doing it for years. In a NOAA study, coral cover was still clearly lower three years after the nets were taken away.

What is a ghost net, exactly?

“Ghost gear” is the everyday name for fishing gear that was lost, cut loose or thrown away at sea. Scientists call it ALDFG: abandoned, lost or otherwise discarded fishing gear. Nets, lines, traps, ropes. Nobody is there to check them, so they just keep catching.

The Global Ghost Gear Initiative, an alliance founded by World Animal Protection and launched in 2015, works on this problem. Modern nets are made of strong synthetic materials, so they do not simply rot away. They can drift for years, even decades. Back in 2009, an FAO press release already said the problem was getting worse, because of these lasting materials and because fishing has become so much bigger worldwide.

How much ghost gear is out there? Honestly, nobody knows. The FAO and UNEP report Abandoned, lost or otherwise discarded fishing gear (2009) says the information is incomplete and does not allow a global estimate. It suggests gillnets and traps or pots may be the most common types. You will see big global numbers online. I left them out, because I could not trace them to a source I could check. I prefer to say “we do not know exactly” than to repeat a number just because it sounds strong.

What a ghost net does to a reef

This is the part that matters most for every place we take guests into the water. In 2023, NOAA researchers published a study in Marine Pollution Bulletin about Pearl and Hermes Atoll, in the Northwestern Hawaiian Islands. They photographed the same reef plots again and again, comparing places where derelict nets had been removed with control sites. Three years after removal, coral cover where the nets had been was still significantly lower. Much of the bare surface left by the nets was now covered by algae, not by new reef-building life.

The authors estimate that about 52 metric tonnes of derelict nets build up in the Northwestern Hawaiian Islands every year, tangled into the reef itself. That is one reef chain, in one ocean.

You do not need to be a scientist to picture how it happens. The surge pushes the net back and forth. It rubs the soft coral tissue, breaks branches, and blocks the light and water flow the coral needs to live. I would not say every reef reacts the same way. But this study shows something important: taking the net away is not the end of the story. The reef under it can need a long time to recover, if it recovers at all.

Who gets caught

A ghost net does not choose. It catches whatever swims into it: fish, sharks, sea turtles. And because nets drift, they can appear very far from where they were lost.

The Olive Ridley Project, a charity working in the Maldives and the wider Indian Ocean, reports (as cited by World Animal Protection) that it and its volunteers have removed over 1,200 ghost nets and rescued over 300 entangled turtles in the region. Net fishing is banned in the Maldives, and olive ridley turtles do not nest there, so these nets are thought to drift in from other places. An earlier count from the project’s first years also said the recorded cases came from chance encounters. So they are probably only a small part of the real number.

The corals underneath take the slower, quieter hit. It shows up later in reef surveys, as a patch of bare rock where a coral head used to be.

What should you do if you find a ghost net while diving?

If you spot a net, wanting to help is a good instinct. But freeing a large animal or pulling gear off a living reef can be dangerous without training, and pulling on a net can break the coral beneath it. This is my own careful advice, not a rule from any authority: keep your distance, do not cut or pull, remember the place and what is caught, and tell your guide, the boat crew, the dive centre or a local marine authority. Many places have trained teams for this work, and they will want to know the location.

If an animal is alive and in trouble, tell the crew straight away. Speed matters, and trained people can act. It is also a good way to see what kind of operator you are with. Do they have a plan for what happens when they find a net?

The conservation and ethical layer

Ghost nets remind us that reef damage is not always about visitors. Most of it starts on fishing boats, far from any tourist. But what we do in the water still counts. We can choose operators who brief their guests, who work with local clean-up groups, and who treat a net as something to report, not something to ignore. And we can make sure we do not add to the damage: fins off the coral, anchors in sand, take nothing, leave nothing. It is the same thinking behind how to snorkel without damaging coral and the wider ideas in how we approach ethical wildlife encounters.

A few simple things help. A well-fitting low-volume mask and snorkel makes it easier to float calmly, look, and stay off the reef. A rash guard protects your skin from sun and small scrapes, so you need less sunscreen. These are practical choices, not solutions. The real work is done by the people who clear the nets, and by fisheries that stop losing them.

What a visit can honestly offer

Reefs recover slowly. For most of us, the best gift is to not add to the damage, and to support the people already doing the removal work. At Ocean Calling we work with vetted local operators, keep groups small, up to six people, and keep the days slow. That leaves time to look carefully, and to notice when something is wrong. If this made you curious to see a reef with your own eyes, you can explore our retreats.

Questions people ask

What is a ghost net?

A ghost net is fishing gear that was lost, abandoned or thrown away at sea and keeps catching animals with nobody there to check it. Scientists call this wider group of gear ALDFG.

How much ghost gear is in the ocean?

Nobody knows exactly. The 2009 FAO and UNEP report says the available information does not allow a global estimate. Be careful with big numbers you see online.

What do ghost nets do to coral?

They can rub and break coral and block light and water flow. In a 2023 NOAA study at Pearl and Hermes Atoll, coral cover was still significantly lower three years after the nets were removed.

Which animals are affected?

Fish, sharks and sea turtles are among the animals caught. The Olive Ridley Project reports removing over 1,200 ghost nets and rescuing over 300 turtles in the Indian Ocean.

Should I try to cut a net free if I see one?

No, not without training. Remember the location and tell your guide, the boat crew or a local marine authority. This is careful advice, so always follow your operator’s plan.

Do visitors cause ghost nets?

Mostly not. Ghost gear comes mainly from fishing. Visitors can still help by choosing careful operators and by not adding damage to the reef.

Wildlife encounters are never guaranteed and never forced. Ocean Calling works only with vetted, ethical local operators, and every animal is free to approach, or not, entirely on its own terms.

Sources & further reading

Further reading on Ocean Calling: How to snorkel without damaging coral · How we approach ethical wildlife encounters · Plastic pollution and marine life · Ocean Atlas

What Ghost Nets Do to Coral Reefs