The environmental group Sea Shepherd says fishermen fired 25 shots at one of its night-vision drones in Mexico's Gulf of California, bringing it down.

Various drones have been employed to patrol the Gulf, also known as the Sea of Cortez, to combat illegal fishing and save the critically endangered vaquita marina, the world's smallest porpoise.

Sea Shepherd has been the target of demonstrations by fishermen in the past, but said the Christmas Eve shooting represented "a new level of violence."

The group said Tuesday that its drone had located four small boats illegally fishing for totoaba, a fish whose swim bladder is prized in China.

The vaquita population has dropped to less than 30 because gill nets set for the totoaba can trap the porpoise.