A man holds two examples of the large shrimp living in waters in the upper Gulf of California, one of the species endangeed by the shrimp-laden boats plying the upper Gulf of California, Puerto Penasco They are fishing in a nationally protected marine reserve.

As leaders from the Pacific rim nations gather in the resort of Los Cabos further south on the Gulf, President Vicente Fox is facing off against angry fishermen in a last-ditch battle to save what Jacques Cousteau once called “the world’s aquarium.”

The battle has affected U.S. tourists, hundreds of whom were prevented from returning to the United States over the weekend when fishermen blocked a highway that connects Arizona with the sleepy port of Puerto Penasco, known among tourists as Rocky Point.

The fishermen formed human chains across the highway after Fox sent in the Navy earlier this month to oust shrimping vessels from the northernmost section of the Gulf of California.

Declared a national park and UN biosphere reserve nearly a decade ago, the million-acre (400,00-hectacre) reserve cuts a glistening blue swath through one of North America’s driest deserts, separating Baja California from mainland Mexico

It is a key breeding ground for the rest of the Gulf, also known as the Sea of Cortez. While better known as a wintering ground for whales, it’s most endangered resident is the vaquita, the world’s smallest porpoise, and a species on the brink of extinction. With less than 600 1.5-meter long Vaquitas remaining, “this is our last chance to save this species,” said Mexico’s Environment Secretary, Victor Lichtinger. That’s where the estimated 500 shrimp boats come in: their huge trawler nets scrape the bottom of the Gulf clean of marine life, dredging up dozens of species on which vaquitas depend. They keep a few commercially valuable species and throw the rest away to die. “Trawling the ocean floor has just completely destroyed this ecosystem,” said Peggy Turk, director of the Intercultural Center for the Study of Deserts and Oceans in Puerto Penasco, which sits just outside the reserve.