Image copyright Paula Olson Image caption Vaquita porpoises are rarely seen

Mexico's government says it plans to use dolphins trained by the US Navy to try to save the world's most endangered marine species, the vaquita porpoise.

Environment Minister Rafael Pacchiano said that the dolphins would be deployed to locate and herd vaquitas into a marine refuge.

Mexico also permanently banned fishing nets blamed for the vaquitas' decline.

Scientists estimate that fewer than 40 of the mammals are still alive in their habitat, in the Gulf of California.

Mr Pacchiano said the dolphin project would begin in September.

"We've spent the past year working alongside the US Navy with a group of dolphins they had trained to search for missing scuba divers," he told Formula radio.

"We've been training them to locate the vaquitas.

"We have to guarantee we capture the largest possible number of vaquitas to have an opportunity to save them."

The Mexican government also said on Friday it was imposing a permanent ban on gillnets, used to catch totaba, which are highly valued in Chinese traditional medicine.

Image copyright Flip Nicklin / Minden Pictures Image caption Could the latest ban on gillnets make a difference?

The nets are designed to trap the heads of fish but not their bodies, but are blamed for trapping and killing the porpoises as well.

Hollywood actor Leonardo DiCaprio, who has campaigned to save the vaquitas, tweeted that the ban was "great news", thanking President Enrique Pena Nieto and environmental group WWF.

A temporary ban which had previously been in place since 2015 was seen as ineffective, leading the WWF to call for it to be extended and properly enforced.