Ghost nets are haunting the oceans, but not in a supernatural way. Sadly, they're real. When fishing nets are lost or abandoned at sea, they often just keep on doing their job, catching and killing all kinds of unfortunate marine creatures (even polar bears).

Mission Blue explains:

“Ghost nets are among the greatest killers in our oceans, and not only because of their numbers. Literally hundreds of kilometers of nets get lost every year and due to the nature of the materials used to produce these nets they can and will keep fishing for multiple decades, possibly even for several centuries. When caught on a reef, nets do not only catch fish, turtles, crustaceans, birds or marine mammals, they also destroy hard and soft corals, wiping out complete ecosystems while swaying in the current.”

Heroic divers free a seal from a ghost fishing net.Heroic divers free a seal from a ghost fishing net. (Photo: NOAA's National Ocean Service)

This means some nets lost at sea during our grandparents’ time might still be causing harm today. These indiscriminate oceanic killers must be stopped, but how?

Groups of divers like the Ghost Fishing Foundation do fantastic work locating and removing ghost nets and other discarded fishing gear, and sharing their expertise with other divers around the world, but they’re fighting against the symptoms of the problem. What if we could solve it at the source?

A new study published in the journal Animal Conservation describes some promising tests done with biodegradable fishing nets. The researchers developed a net made of a blend of 82 percent polybutylene succinate (PBS) and 18 percent polybutylene adipate-co-terephthalate (PBAT) and compared its fishing efficiency with conventional nets. (If you can’t convince fishermen that these nets will do as good a job as regular, non-biodegradable nets, this is a pointless exercise.)

During lab testing, the biodegradable nets had inferior theoretical performance to the regular nets (they had lower breaking strength and were stiffer), but during actual fishing they performed similarly to regular nylon monofilament nets and started to biodegrade after 24 months in seawater. This is only a first step. More testing needs to be done, and the biodegradable materials could no doubt be improved to better match the performance of conventional nets, but these tests were promising enough to show that this solution should be pursued further.

When it comes to ghost nets, the best long-term outcome for ocean conservation would probably be the creation of global regulations mandating biodegradable nets, along with enforcement of the rule (always a problem out at sea). In the meantime, fishing boats should make sure their nets are attached extra-securely and never dump old damaged nets into the water.

Michael Graham Richard ( @Michael_GR ) Michael writes for MNN and TreeHugger about science, space and technology and more.