Dozens of fishermen have burned a boat as part of a threat to force out a ship operated by the Sea Shepherd Conservation Society in Mexico's Gulf of California.

Sea Shepherd has been removing illegal and abandoned nets that endanger the vaquita, the world's smallest porpoise. Illegal fishing for the totoaba, another species, has reduced the number of vaquitas to fewer than 30.

Fishermen in the town of San Felipe painted the name of the Sea Shepherd on an empty, open fishing boat they burned Sunday. They threatened to remove the conservationists' ship themselves if the government doesn't.

"Just as they are judging us fishermen, we will judge all the environmentalists," said Sunshine Rodriguez, a leader of the local fishing cooperative in San Felipe, Baja California. "We aren't going to just sit around."

A speaker at Sunday's protest — which drew hundreds of onlookers and supporters at San Felipe's main waterfront boulevard — said over a loudspeaker, "I'm giving them (the government) five days to get this boat out of our territorial waters, or we will do it ourselves.

The fishermen were angered by conservationists' calls for a boycott of Mexican shrimp, and possible plans to permanently ban all gillnet fishing in the area. Vaquitas get caught in nets set for the totoaba, a fish prized in China for its swim bladder. The dried bladders can fetch thousands of dollars per kilogram (2.2 pounds).

Oona Layole, the captain of the Sea Shepherd ship, said Monday her vessel is planning to stay despite the threats, but noted "the atmosphere is tense."

"I was expecting to get some reaction from the fishing communities, but it is shocking that these people feel that they can publicly express violent threats to us, such as burning our ships," Layole said.

The situation has already turned violent. In early March, a gang of dozens of fishermen overturned inspectors' trucks and burned or destroyed 15 vehicles and patrol boats, as well as beating three inspectors from the office for environmental protection in another town on the Gulf of California, which is also known as the Sea of Cortez.

Then, on March 16, a coalition of U.S. environmental groups launched a call to boycott Mexican shrimp — one of the country's most lucrative seafood exports — to pressure the government to do more to save the vaquita.

Conservationists are pressing Mexico's government to permanently ban all gillnet fishing in the upper Gulf, the only place in the world the vaquita is found. Partial and temporary bans are already in place.

The Sunday demonstration also featured fishermen holding up banners with the names of prominent conservationists, researchers and scientists, on a list of enemies.

In other parts of the world, Sea Shepherd vessels have rammed whaling ships. But in the Gulf, the group's ship has peacefully patrolled the waters, looking for vaquitas — finding some dead and some alive — and illegal nets, which it removes.

A government official who was not authorized to be quoted by name said Sea Shepherd was working jointly with the government to withdraw nets and report illegal fishing, and said the group had been a valuable ally in the effort. The official said authorities would step up protection for the campaign.

Totoaba fishermen have mainly cut and run when confronted by Mexican Navy patrols in the past, but activists and environmentalists have warned that criminal gangs appear to be involved in the lucrative illegal trade and that threats have been mounting.

Last week the government said poachers are using go-fast boats, and in one case led authorities on 50-mile chase, and parked a pickup truck on a beach to load the boat and try to escape.

Experts and the Mexican government previously announced a plan to catch the few remaining vaquitas and enclose them in pens for protection and possible breeding.

Experts acknowledge the catch-and-enclose plan is risky, because the few remaining females could die during capture, dooming the species.

Still, some experts say the capture program may be the vaquitas' only hope. But others worry that fishermen may engage in a free-for-all once the endangered vaquita is removed and thus wipe out other species in the gulf.