Underwater（水下） salvage（抢救财货）. Divers recover ghost nets from the depths of the sea. These old fishing nets become deadly traps for millions of marine（海的） animals. They become plastic waste that can poison oceans for centuries. And they cause agonizing deaths above the surface, too. What's the solution to this dangerous problem?

  How can we stem（起源） the global tide（潮） of ghost nets? The ship Goa leaves Glova Harbor on the island of Rugen. On this summer's day, the small salvage vessel（船） is on a special mission in the Baltic（a波罗的海的） Sea. It's being escorted（ 护送） by a boat full of divers, aiming to recover ghost nets. Ghost nets are abandoned fishing gear（齿轮）. Even though they're not being used anymore, they're still very efficient at killing, which of course makes（使） no sense because there's no purpose for it.

  If a dolphin or a papus gets snagged in one, it drowns（淹死）, because it can't reach the surface. Verena Platt works for GRD, a German dolphin rescue organization. The environmental NGO regularly conducts ghost net recovery missions in the Baltic Sea. Verena Platt organized today's effort. I first had a scuba tank on my back at age five. Over the years, I've seen how the marine world has changed.

  There's a decline in species. I used to see seahorses, sea bream, all kinds of animals. Today, it's getting harder and harder. Ghost nets are among the causes of this decline. In the Baltic Sea alone, up to 10,000 nets or parts of nets come ashore（在岸上） every year. Often, they've been lost in storms or accidents, or snagged on wrecks or other obstacles.

  Each year, up to one million tons of new ghost nets are estimated to go into the world's oceans. As a result, more than 130,000 whales, dolphins, seals（封蜡） and sea lions, as well as millions of fish, turtles and birds, die every year. Around the world, about 800 species are affected. Add to that the countless（无数的） smaller organisms that are vital for marine（海的） ecosystems. The GRD works with experienced divers who know the local area. They take part at their own risk.

  We're at 45 meters, nearly there. Today's operation is led by Wolfgang Frank. He's a professional diver who's been running a diving business on Rugen for 25 years. The boy's in place, so you can start getting ready. We've clarified the target below the red boy. There's a big pile there, a torn part of a trawling net.

  On his many dives, Wolfgang Frank always keeps an eye out for ghost nets. A few months ago at this spot, I found bits of net where things like cod can get caught. There's a long steel cable, and the net is caught on that. We want to bring it up. And that's why we're here. They locate the steel cable at a depth of around 10 meters.

  The net is wrapped tightly around it. It will be difficult to get it free. Another problem is the poor visibility（能见度）. The visibility here in the Baltic makes things very, very difficult. There are a lot of algae（[植] 藻类） residues（残余） in the water, algal blooms caused by the warming of the Baltic Sea. When we dive for a net, the visibility is still okay, like three or four meters, so we can orient（ 确定方向） ourselves.

  But as soon as we touch the net, we really have zero visibility, then you more or less have to feel your way around. The net is cut into pieces, partly to reduce the risk of a diver getting entangled（使缠上）. At the next site, caution（ 小心） is once again needed. There's part of a trawler net there. On top is an old trap anchor（锚）, or an old metal frame. We're going to try to lift the frame first, and then get the bit of trawler net, or whatever else is down there.

  The net is very difficult to separate from the anchor. It's a back-breaking job. You never know what's going to be down there, especially when it comes to trawler nets, which naturally work their way into the seabed（海底）. When we put our buoyancy bag there, we can only see a little bit of the upper part. We can't see everything that's there in the seabed. The anchor is extremely heavy.

  The divers have to install several buoyancy bags and fill them with air. Visibility is terrible, and it's still not clear whether the recovery will be a success. Ghost nets aren't only a problem in the sea itself. Their remnants（残余） also end up on the world's coasts, including the beaches of the North Sea, like here near the popular resort town of St.Peter Oding. This is a typical bit of net from the local fishery（渔业）. We find these everywhere along the coasts and wherever there's intensive（加强的） fishing, like around the British Isles or here in the Wadden Sea.

  These ghost nets wreak havoc（ 大破坏） for decades or even centuries because they're so strong. They're made of plastic. This one's probably polyamide. Very robust（精力充沛的）. It can take from 200 to 600 years to decompose（分解）. Kim Detloff regularly walks along various North Sea beaches to monitor them on behalf（ 利益） of the Nature and Biodiversity（生物多样性） Conservation Union.

  He finds plenty of trash in the process. On these beaches, we find about 150 pieces of trash per 100 meters of coastline. Thirty to fifty percent of that is from the fishing or shipping（[船] 船舶） industries. Ghost nets don't only pollute beaches and kill marine life. They're also plastic waste. And over time, they break down into microplastics.

  That means they travel through the food chain and end up on the plates of us humans. Each time Kim Detloff goes to the beach, he also finds lots of smaller pieces of brightly colored netting. This is very common. It's called a dolly rope. It's used during bottom trawling to protect the net, which is more valuable, more expensive. Bottom trawling for a flatfish（比目鱼） or crabs involves dragging the net over the seafloor（海底）, over stones and beds of mussels（蚌）.

  So there's abrasion（磨损） and wear. That's why they put this dolly rope underneath. It amounts to a deliberate littering of the oceans, pure and simple. Each year, an average of around 25 tons of dolly rope end up on European beaches. The dolly rope problem is quite well known in the fishing industry. About 70% of German fishing boats no longer use them.

  But it's still widely used in the Dutch（荷兰的） fishery（渔业）.