For nearly two decades, Edgardo Ochoa has picked away at a problem.

A net here, some fishing line there — Conservation International’s marine and diving safety officer has single-handedly scooped up thousands of pounds of abandoned fishing gear from the bottom of the sea.

It’s impressive, but it’s not nearly enough to make a dent: According to one estimate, nearly a third of fishing lines are lost or discarded at sea. This so-called “ghost gear” — along with lost nets and traps — is deadly for marine animals. Experts estimate that more than 300,000 whales and dolphins die each year after getting tangled in them. Once, Ochoa saw a whale caught in a fishing net that ended up severing its tail.

With far more “ghost” nets than any one person can possibly handle, Ochoa created a course to teach recreational divers how to safely remove ghost gear from the sea.…