Researchers from the Commonwealth Scientific and Industrial Research Organization said around 640,000 tons of fishing gear is lost or discarded each year, mostly from fisheries in Asia and Australia.
The nets are a particular problem in the Gulf of Carpentaria off northern Australia, they said, although they are a global threat to seabirds, marine mammals and turtles.
During a recent cleanup of ghost nets on beaches in the Gulf, 80 percent of animals recorded in nets were marine turtles, China's Xinhua news agency reported Monday.
"Using a model of ocean currents and data collected by indigenous rangers on the number of ghost nets found during beach cleanups, we simulated the likely paths ghost nets take to get to their landing spots on beaches in the Gulf of Carpentaria," CSIRO researchers Denise Hardesty said.
In the Gulf, ghost nets can reach a density of three tons of net per square kilometer, the researchers said.
"Our research shows that combining models of marine debris with species occurrence data could identify global hot spots for impact, helping pinpoint where prevention and clean-ups could really make a difference to biodiversity," Hardesty said.