How Now, Little Cow?

The vaquita, the world's smallest porpoise, lives only in the northern Gulf of California. With just 200 individuals remaining, can the species survive?

Vaquita Mother and Calf 2

Lithograph of vaquita mother and calf was created in 1997 to support vaquita conservation.

William Shepard

But the vaquita has no reason to smile. The world population of vaquitas is probably about 200 individuals—you can see more people in a Wal-Mart on a busy weekend. And though Wal-Martians are definitely in no danger of extinction, the vaquita is losing market share. Gill nets—nearly invisible fishing nets set in the water like curtains and often left unattended—are the single greatest cause of vaquita mortality each year. Vaquitas become entangled and drown when they swim into the nets by accident; or they might be lured there by fish that are already stuck. Vaquitas aren’t the intended targets of any fishery; they’re merely the bycatch of local fishermen trying to earn a living—collateral damage.

With the vaquita’s population in steady decline, its distribution in the northern gulf has also contracted, so that its range is now the smallest of any marine mammal. Nearly the entire population lives in a region less than forty miles across. To put that into perspective, while on surveys throughout the gulf, we have seen a few dozen vaquitas over the years. But never have we seen one without being able to look up and see Consag Rock, a 300-foot-tall, guano-covered spire in the middle of the northern gulf.

Even the vaquita’s scientific name, Phocoena sinus, acknowledges its claustrophobic range. Phocoena is derived from both the Greek and Latin words for “porpoise”; sinus is Latin for “bay” or “pocket,” and refers to the animal’s restricted home waters. (The common name, vaquita, means “little cow” in Spanish—a rather fitting name now that biologists know that all cetaceans are the product of a successful re-invasion of the ocean by terrestrial ungulates.)

At a recent forum convened in San Diego to address the fate of the vanishing vaquita, the organizers displayed a gallery of nearly every known photograph of the species. Most showed a dead animal swaddled in gill net in the bottom of a fishing boat, that innocent smile frozen on its face in death as in life. There were only a couple of photographs of live animals, and they were no more than blurred images of a head or a dorsal fin hastily rolling out of sight in the distance. We were struck that a large mammal living in our time could be driven off the planet forever, and leave behind such a scant record that it was ever here.

Dead Vaquitas

The first fresh vaquita specimens to be photographed, these animals were the basis for the description of the species’ external morphology. A calf is in the foreground; the adult just beyond it is as big as this species gets.

Alejandro Robles

The best estimate of the world’s vaquita population to date comes from a 1997 shipboard survey of the vaquita’s known range, which was conducted by the U.S. National Marine Fisheries Service in collaboration with Mexican investigators. From the survey data, Armando Jaramillo-Legorreta, a Ph.D. candidate in oceanography at the Autonomous University of Baja California in Ensenada, and several of his colleagues estimated the vaquita population at 567 individuals.

To determine whether the population is growing, declining, or holding steady, one must know, among other things, its mortality from both natural and human causes. The latter is essentially the number of animals that die in nets every year, and that critical piece of information was supplied by Caterina D’Agrosa, now a postdoctoral fellow at Arizona State University in Tempe. Between January 1993 and January 1995, as part of her master’s thesis, D’Agrosa had interviewed fishermen and placed observers aboard fishing boats, primarily in El Golfo de Santa Clara, one of the three main fishing communities in the northern gulf. Extrapolating from her sample, she estimated that seventy-eight vaquitas were being killed annually, an overall population decline of about 10 percent per year. At that rate, a population of 567 individuals in 1997 would have plummeted to about 200 by now.

Beyond those population estimates, and despite numerous surveys to observe vaquitas in the wild, little is known about their biology or life history. Because the animal is shy as well as rare, it has not readily disclosed its secrets. But what little is known does not bode well for its future. The normal lifespan is probably twenty years or more. It reaches sexual maturity between three and six years of age, and females apparently give birth to a single calf every other year. It typically travels alone or in mother-and-calf pairs. A recent study determined that the species has little or no genetic diversity; it may have passed through a population bottleneck at some time in its past, or evolved from a small founder population. The combination of low numbers, late maturity, low birth rate, and low genetic diversity makes the vaquita vulnerable to extinction, even without such strong pressure from people.

view counter
view counter

Recent Stories

Fossilized cell remnants in 3.4 billion-year-old bedrock are from primitive microbes. 

Frog hoppers piercing plants with their mouthparts produce negative pressures exceeding a megapascal. 

An Okinawa citrus species arose two million years ago when the Ryukyu archipelago disconnected from Asia.

Astronomers have detected a disk around a planet outside our Solar System for the first time.