Crew from six fishing boats in Mexico's Sea of Cortez were arrested by the Mexican Navy, after they were caught using illegal fishing nets to poach banned fish in a marine reserve.

The fishermen had been spotted by the Sea Shepherd vessel Farley Mowat, which tracked the six boats until navy officials could arrive on the scene.

According to Sea Shepherd, a nonprofit marine wildlife organization, the fishermen were using banned gill nets to catch totoaba bass, a rare fish Mexican law has protected since 1975 but one that is nonetheless poached for its swim bladders, which, at an estimated US$20,000 per kilo, fetch a high price on China's black market.

The fishing boats were stopped and their crews apprehended without incident.

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The Sea of Cortez, also known as the Gulf of California, is the home to the vaquita porpoise, a rare species on the verge of extinction, with only an estimated 60 left.

The illegal gill nets used by the poachers are a major problem for the vaquita and have greatly contributed to their decline. The thin lines are dropped vertically into the sea and while they trap totoaba they also ensnare other marine life, such as the vaquita, as bycatch. Vaquita need to surface for air, and they can drown when the nets prevent them from swimming back above water to breathe.

In July 2016, the Mexican government made permanent its ban on gill nets, extending forever an emergency ban imposed in 2015.

The Farley Mowat and another Sea Shepherd vessel, the Sam Simon, are currently working the waters of the Sea of Cortez, seeking out poachers fishing in protected areas.

"Sea Shepherd's partnership with the Mexican Navy is achieving results," said Sea Shepherd's founder and CEO Captain Paul Watson, in a statement. "Every poaching vessel intercepted and arrested is one step closer to preventing the extinction of the vaquita."

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