Mexico City - The World Wildlife Fund has called for a complete ban on fishing in the habitat of the vaquita porpoise, noting an international committee of experts has determined that fewer than 30 of the critically endangered mammals probably remain in the upper Gulf of California, the only place they live.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.Swim bladderBut the WWF argued that is not the answer for the tiny porpoise, saying in a statement that "the only way to save the vaquita from extinction is for the Mexican government to immediately and indefinitely ban all fisheries within its habitat."That would be a politically and economically costly move for the government. Mexican authorities already banned gillnet fishing in the vaquitas' habitat, but that has proved difficult to enforce.The WWF published a link to a study done in November by an international committee of experts that used acoustic monitoring to survey the population of the porpoise. The results showed vaquita numbers had declined 90% over the last five years and the study estimated that because numbers have dropped so fast there are probably less than 30 now.Fishermen lured by Chinese demand for the swim bladder of a fish known as the totoaba, which inhabits the same waters as the vaquita, have decimated the porpoise population. Vaquitas are caught in the same kind of nets that illegal totoaba fishermen use.The international committee found that illegal fishing continues, saying 31 illegal nets were pulled from the Gulf of California, which is also known as the Sea of Cortez, in October and November.Saved speciesThe WWF called on Mexico's government to extend the gillnet ban and also stop net fishing for corvina, a season that will open soon.The group also urged the US government "to take swift and decisive action to stop trans-border shipments of totoaba products" and called on the Chinese government "to immediately stop the illegal transport and sale of totoaba products."Experts acknowledge the catch-and-enclose plan is risky, because the few remaining females could die during capture, dooming the species. Breeding in captivity has successfully saved species such as the red wolf and California condor, but the vaquita has only been scientifically described since the 1950s and has never been bred or even held in captivity.