The total size of fishing nets lost or discarded in the ocean every single year is equal to the size of South Carolina, scientists have estimated.

Designed to be durable and long-lasting, lost or discarded fishing gear is a major contributor to ocean pollution and its harmful effects can be seen in the estimated 300,000 whales and dolphins that are killed due to fishing gear entanglement annually, according to the World Wildlife Fund (WWF).

Lost fishing gear also produces an alarming amount of microplastics—tiny, pervasive plastic particles that have increasingly been found almost everywhere on Earth, from the summit of Mount Everest to the fetuses of pregnant women. One study found that the fishing fleet of the United Kingdom alone may be releasing anywhere from 326 million to 17 billion microplastic fragments from fishing rope every year.

In a new study published in the journal Science Advances on October 12, researchers in Australia calculated that a staggering 75,000 square kilometers (28,957 sq. miles) of purse seine nets—a large wall of netting that is deployed around an entire area of fish—may be lost to the ocean every year.

This is in addition to just under 3,000 square kilometers (1,158 sq. miles) of gillnets and 218 square kilometers (84 sq. miles) of trawl nets.

Taken together, this area of netting is around the same size as the U.S. states of Maine or South Carolina in terms of square miles.

The pollution does not stop there. The researchers also estimated that 459,555 miles of longline fishing line is lost to the ocean annually—enough to stretch from Earth to the moon and nearly all the way back again—as well as 25 million pots and traps.

The figures are based on interviews with 451 fishers from seven countries about their annual gear usage and losses. These reported loss rates were then multiplied to a worldwide scale based on global fishing effort data.

The interviews suggested that even a single fishing vessel loses around 58,000 square meters of purse seine nets every year on average.

Tamara Galloway, chair in ecotoxicology at the University of Exeter in the U.K., told Newsweek the numbers were "staggering" and "reflect the reality of the global population's reliance on seafood."

She said that lost or discarded nets particularly pose risks from "ghost fishing," in which marine life becomes entangled and dies. As well as causing animal suffering, this phenomenon also leads to substantial losses of protein sources as well as habitat loss.

"There have been some very successful interventions around biodegradable nets made out of waste biomass, 'fishing for litter' plastic waste recovery projects, floating harbor litter bins etc., but not all countries are inclined to legislate for these," Galloway said.

"Our recent research in the remote Galapagos Island for example, found microplastics right across the base of the marine food web, and we've also quantified microplastics in high value seafood intended for human consumption in Australia, showing that what we throw away really can come back to harm us."

Coleen Suckling, assistant professor in sustainable aquaculture at the University of Rhode Island, told Newsweek: "Fishing gear is often designed to be resilient to the harsh conditions of the ocean and to handle a lot of weight, but this often means that some of these lost materials and equipment will continue to exist for long periods of time."

Suckling said that ghost fishing due to lost or discarded gear can affect vulnerable species such as sea turtles, sharks, rays, seabirds, and marine mammals.

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