Taking advantage of the acoustic signals vaquitas use to find food, researchers monitor the population of an animal on the brink of extinction.
By Kate Wheeling
1(Photo: Wikimedia Commons)
The vaquita — the aptly named “small cow” of the sea — is one unlucky porpoise. Already the most endangered marine mammal in the world, the animal’s entire current range overlaps with prime fishing and shrimping territory for coastal villages along Mexico’s Gulf of California, whose economies rely heavily on small-scale fisheries. The Mexican government established a Vaquita Refuge in 2008 to protect the porpoise, but by 2011 there were approximately only 200 vaquitas left on Earth. And a new study, published this week in Conservation Biology, has found that the number of vaquitas may have fallen by another 80 percent over the last five years.
The main driver of the vaquita decline is bycatch. Often, the porpoises became entangled in fishing nets meant for other species, like the gillnets used to catch the totoaba fish in the Gulf of California. Even fishing bans haven’t been able to stop a black market boom for the swim bladders of the totoaba — a delicacy in China that can sell for up to $5,000 a piece—which means vaquitas have continued to be unfortunate (and unintended) victims.
Conservationists have a vested interest in keeping track of the dwindling number of vaquitas, but because the small porpoises are now so rare, visual surveys to monitor their population levels have become all but useless. Luckily, vaquitas are echolocators, which means they emit acoustic signals, or clicks, into the environment. (They observe how the sound waves bounce back to detect prey.) Researchers can listen in on those signals to estimate the abundance—or lack thereof—of vaquitas.
The number of vaquitas may have fallen by another 80 percent over the last five years.
In the new study, the researchers deployed an array of 48 acoustic detectors in the Vaquita Refuge to record the animals’ clicks between 2011 and 2015. The recordings were limited to three months out of the year after a pilot study found that, during fishing seasons, many of the acoustic detectors were lost within the Refuge, suggesting illegal fishing was still taking place. The researchers accounted for various confounding factors such as changes in season, time of day, and tidal state, so that any trend in click rates could be attributed to the number of vaquitas.
A statistical analysis of the data revealed a “catastrophic decline” in the vaquita population, according to the authors. From 1997 to 2008 — when the Vaquita Refuge was established — the vaquita population dropped by less than 8 percent per year. But between 2011 and 2015, vaquita acoustic activity — a proxy for vaquita abundance — dropped by an average of 34 percent per year.
In 2014, the authors released a preliminary analysis of the data, prompting the Mexican government to ban the use of gillnets for two years, and to set aside approximately $74 million to reimburse fishers for lost income. Such bans in the Gulf of California and elsewhere could save more than just the vaquitas. “If the vaquitas are lost, it will not be the last cetacean species to go extinct in the near future,” the authors write. “The most endangered populations of porpoises and dolphins in the world suffer from similar gillnet threats.”
||
