Nine Gulf of California harbor porpoises, a rare marine mammal known in Mexico as the "vaquita," or sea cow, were sighted by Environment Secretariat specialists in that narrow sea, the secretariat said.

The members of the Phocoena sinus species, listed by the International Union for Conservation of Nature as critically endangered, were discovered in the northern part of the Gulf near the Roca Consag outcrop and included three young vaquitas and a newborn.

The porpoises were spotted near a refuge for vaquitas, which inhabit shallow Gulf of California waters off the coast of the northwestern Mexican states of Baja California and Sonora, the secretariat said.

The small marine mammal, which weighs some 50 kilos (110 pounds) and measures 1.5 meters (five feet) in length as an adult, typically calves every two years and has been seen just a handful of times over the past decade.

Its numbers fell from several thousand to close to 600 between 1958 - when U.S. biologists came upon several skulls of this then-unknown species - until an initial census was conducted in 1997.

The first entire specimens of the Phocoena sinus - considered the world's most endangered cetacean - were found in 1985, although the animals were already dead.

The sighting is an "incentive to continue and strengthen programs to conserve this species," Environment Secretary Juan Rafael Elvira Quesada said.

"Different sectors of society, including state and municipal authorities and civic organizations, both domestic and foreign" participate in these programs, the secretary said.

Around 425 million pesos ($32.6 million) have been invested to date to conserve the vaquita, leading to the removal of 247 small boats and the replacement of nets with other fishing methods, Elvira Quesada said.

The vaquitas were spotted in three groups - one with five porpoises and two with a pair of animals each - while a team of experts was removing acoustic detection equipment used to monitor them.

Fishing nets have been banned since 2008 inside the vaquita refuge area of the upper Gulf of California, which had been established three years earlier.