Habitat

Humans have left their mark from fishing, pollution and climate change on every ocean habitat, from the shoreline to the deepest point on the planet, the Mariana Trench, where 7 miles (11km) below the surface, explorers have found plastic trash littering the seabed.

Overfishing: Nearly 90 percent of all commercial fish stocks are fully exploited or overexploited, according to a 2016 United Nations report. Fish stocks that are being exploited at unsustainable levels have jumped from 10 percent in 1974 to 31.4 percent today. Those stocks include Pacific, Pontic shad in the Mediterranean and Indian mackerels in the Eastern Indian Ocean.

The high cost of seafood caught by bottom trawling. Credit: Seafood Watch.

Even as fish populations decline, new fishing techniques have allowed the capture of other species previously out of reach. For instance, bottom trawlers drag huge nets along the ocean floor to gather species like orange roughy. But bottom trawling can also damage coral reefs and seamounts, decimating populations of deep-sea fish that take years to mature and reproduce. Gill nets – hung vertically to capture fish by their gills – and long lines – which consist of thousands of baited hooks that can stretch for more than 50 miles (80km) – allow commercial operators to meet a growing demand for seafood but at a great ecological cost, as millions of sea turtle, sharks, marine mammals and other species are inadvertently killed each year as bycatch.

Shipping: More than 90 percent of global trade is transported by ship, according to the International Maritime Organization. From 1990 to 2015, the tonnage carried by sea more than doubled to 10.8 billion metric tons and as of January 2016, 51,400 merchant ships traversed the world’s oceans. That growth has fueled economic development and brought prosperity to developing countries. It has come, however, at an environmental cost. Shipping is responsible for about 3 percent of global carbon dioxide emissions. Container ships also transport large volumes of seawater that they take on as ballast to balance cargo loads. Ballast water has moved species around the world, some of which, like zebra mussels, can severely damage native ecosystems and infrastructure. Officials at one Texas water district, for instance, pegged the cost of building a new mussel-free pipeline at $350 million.

Noise: Scientists have found that the deafening underwater noise generated by ship propellers can harm whales and dolphins, which rely on sound to communicate, navigate and find food. As shipping traffic has grown, so have the risks of fatal collisions with endangered whales.

Plastic Pollution: An estimated 8 million metric tons of plastic washes into the world’s oceans annually, and by 2050, there may be more plastic in the ocean than fish by weight, a 2016 report estimated. The epicenters of plastic pollution are the five rotating gyres of water that draw water, and anything floating in it, into areas as large as 15 million square miles (39 million square kilometers). The most famous of these is the North Pacific Gyre, colloquially known as the Great Pacific Garbage Patch. But plastic trash has been found throughout the seven seas, from 36,000ft (11,000m) below the surface to the farthest reaches of the Arctic Ocean.

Pierre Huguet/Biosphoto

Large pieces of plastic trash harm wildlife – plastic bags look so much like jellyfish that sea turtles will eat and choke on them – and have been found in the stomachs of whales, dolphins and birds. Once plastic is broken down into microparticles – anything smaller than 5mm – it can leach chemicals like bisphenol A (BPA) and polychlorinated biphenyls (PCBs), both of which have been found to have a deleterious effect on human and animal health.

Deep Sea Mining: The deep ocean is rich in biodiversity – and mineral wealth. Millions of polymetallic nodules cover the Pacific Ocean floor, resembling Easter eggs but filled with valuable manganese, nickel and cobalt. Around deep sea hydrothermal vents are deposits of gold, copper and rare earth metals needed to manufacture smartphones, laptops and other electronics. British scientists have discovered that a single seamount in the eastern Atlantic Ocean contains concentrations of tellurium – used to make solar panels – 50,000 times greater than found on land.

Deep ocean minerals have long remained out of reach, but technological advances have now made seabed mining commercially feasible. The International Seabed Authority, chartered by the U.N. to regulate mining in international waters, has so far issued 15-year exploration licenses to 25 corporations and governments covering 491,122 square miles (1.3 million square kilometers) of the ocean floor. Mining may not proceed until regulations are finalized – expected by the end of 2018, but environmentalists fear that a gold rush to mine the seabed will destroy fragile habitats and marine life that scientists are only just beginning to discover. For instance, in December 2016, scientists announced they had found that a newly discovered species of ghostly white octopus lays its eggs on sponges that grow on polymetallic nodules on the ocean floor near Hawaii.

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