MEXICO CITY (AP) — The conservationist group Sea Shepherd said Friday that two fishermen were injured off Mexico’s Baja California coast when they rammed their small boat into a larger vessel used by the group in efforts to protect the endangered vaquita porpoise.

The attack is the latest round in an escalating spiral of protests by fishermen who use banned gill nets in the Gulf of California, the only place the vaquita is found. Only as few as a dozen vaquitas are believed to remain, making them the world’s most endangered marine mammal.

Fishing nets confiscated by Sea Shepherd vessels are expensive, so fishermen often harass the conservationists’ boats to try to get them back. The fishermen claim they have not received compensation from the Mexican government for lost fishing income. Groups representing fishermen were not immediately available to comment.

Sea Shepherd said its vessel, the Farley Mowat, was pulling illegal gill nets out of the waters of the gulf, also known as the Sea of Cortez, on Thursday when people on a group of about a half dozen small, open fishing boats began tossing gasoline bombs at the vessel, setting the bow and another part of the ship afire.

The attackers also threw lead net weights at the crew, the group said.

It released a video showing one fishing boat approaching the Farley Mowat at high speed and slamming into the side of the vessel.

Two of the boat’s occupants were pulled from the water by Sea Shepherd crew members and Mexican marines, who usually accompany the crew on such trips. One was given resuscitation, because he wasn’t breathing, and both were taken by the navy to a hospital.

Mexico’s navy confirmed the injuries occurred in a “collision,” and distributed photos of the men being flown in a helicopter for treatment, but did not provide details on their condition.

Two other men boarded the Farley Mowat and threatened the crew and marines, the group said.

“This morning’s attack is the latest in a series of increasingly violent assaults launched against Sea Shepherd’s ships over the past month,” Sea Shepherd’s statement said. “Assailants have hurled Molotov cocktails, knives, hammers, flares, bottles of fuel, and other deadly projectiles at the vessels, crew, and military personnel on board. No serious injuries have occurred prior to today’s incident.”

Sea Shepherd works closely with Mexican authorities on the net-removal effort, but fishermen have become increasingly unafraid of confronting marines and sailors.

The vaquita population has been dramatically reduced by illegal net fishing for the totoaba, whose swim bladders can sell for thousands of dollars in China.