Females arrive to give birth, and males come to protect their mates. Some enviromentalists say the lagoon's salinity is slightly higher than the ocean's average of 3.5 percent, helping make it a healthy nursery for whales. After a 5,000-mile migration that begins off the Alaskan coastline, expectant mothers enter the lagoon's slightly warmer waters, where they float more easily and can be assured their newborn will rise to the surface almost immediately to take its first breath. For weeks, the newborns consume only their mother's milk, a nutrient-rich liquid with 55 percent fat content. The babies gain about 50 pounds a day and build muscular strength in an area free from nets, tankers or predators.
Locals insist that successive generations of whales return.
Murillo and other fishermen know certain whales by telltale dark patches or jagged harpoon scars. The older, wounded mammals are part of the small group that until 1994 was on the endangerd species list, residents said. They learned afterward, however, that the gray whale was again in danger. A Mexican enviromental group discovered that a subsidiary of Mitsubishi Inc. was developing plans to build the world's largest salt factory in Laguna San Ignacio. Partly because of protests from Grupo de los Cien, the Mexican enviromentalist group, the agency said the plant might violate the tranquility of the world's last undeveloped gray whale calving area.