The plight of the vaquita

If awards were given to cetaceans, the vaquita (Phocoena sinus) would certainly win a few.  With females reaching lengths of just 1.5 meters, and males 1.4 meters, they are among the smallest of the porpoises in the world.  Found only in the northern part of the Gulf of California (Mar de Cortés), Mexico, their “core area” spans just 2,500 square-kilometres, making them among the most endemic.  They also occupy the warmest waters out of any of the porpoises, and with extra skeletal digits in both flippers, it is also the only consistently bilateral (appearing on both sides) polydactyl (having many digits) cetacean known.  This tiny porpoise is also among the most recently “discovered” of the cetaceans, only formally described by the scientific community 58 years ago. 

 Two vaquita in the Gulf of Mexico. Image credit:  Paula Olson /NOAA, and cropped by WolfmanSF/Wikimedia (Public Domain)

Two vaquita in the Gulf of Mexico. Image credit: Paula Olson/NOAA, and cropped by WolfmanSF/Wikimedia (Public Domain)

Not all of the awards this tiny porpoise could gain are cause for celebration.  In 2006 vaquita took the title of the world’s most endangered cetacean.  It is currently listed by the International Union for Conservation of Nature (IUCN) as ‘critically endangered’, as one of the top 100 Evolutionary Distinct and Globally Endangered (EDGE) mammals in the world, and afforded the greatest level of commercial trade restriction available under the Convention of International Trade in Endangered Species of Wild Fauna and Flora (CITES).  Despite heightened awareness of the plight of the vaquita, many fear it may end up the way of the baiji (Lipotes vexillifer) freshwater dolphin of the Yangtze River in China – functional, if not global extinction. 

Although these rather endearing if elusive cetaceans have been seen down to depths of 50 meters and up to 25 kilometres off the coastline, they are usually found in the Gulf of California’s shallow, often murky coastal waters and lagoons, moving through waters just a few meters deep to around 30 meters.  Whilst these turbid conditions, coupled with their shyness and rarity, make them difficult to spot, the conditions are ideal for feeding.  Surrounded by desert, a warm climate, and home to an upwelling system, this semi-enclosed sea has high rates of primary productivity, giving rise to high levels of biodiversity.  Vaquita are known to feed on some 21 different species of benthic and demersal cephalopods and bony (teleost) fishes, some of which themselves are considered endemics, such as corvina (Isopisthus altipinnis) and midshipman toadfish (Porichthys mimeticus). 

The vaquita’s scientific name ‘sinus’ is Latin for “recess”, “bay”, or “pocket”, aptly describing their limited range in the Gulf of Mexico.  Arguably it could also describe their evolutionary history.  With existing DNA samples for vaquita becoming increasingly degraded and limited opportunities to obtain new samples due to the Vaquita’s small population size and elusiveness, the opportunity for DNA analysis has been difficult.  Fortunately, in more recent years, technology has allowed NOAA to extract genetic material from degraded, single-stranded DNA, opening up opportunities to learn more about the vaquita than thought possible.  This new analysis has already confirmed knowledge garnered from DNA samples studied in the 1990s.  Vaquita are most closely related to a porpoise that is now most geographically distant - Burmeister's porpoise (Phocoena spinipinnis), an endemic to the South American coast.   It is thought that a small number of Burmeister’s crossed the equator into the Gulf some 2 – 3 million years ago during the Pleistocene cooling.  Over time, this group adapted to the Gulf’s rather unique conditions, eventually becoming a unique, genetically distinct, species in its own right.  The evolutionary adaptations are many.  Alongside living in the warmest waters of any porpoise, they are also uniquely able to tolerate the seasonal fluctuations in sea temperature, which ranges from 14º Celsius in January up to 30º Celsius in August.  They also sport the second proportionally highest and widest dorsal fin of any porpoise.  This huge fin is thought to form part of a vascular counter-current heat exchange system, helping the vaquita keep cool in the Gulf’s warm waters.  The historically low population size is thought to explain the vaquita’s polydactyly, which in other mammals normally occurs as a result of inbreeding, as well as its low genetic diversity. 

Whilst the vaquita seem to have survived at fairly low numbers for an extremely long time, this does not mean that their population can be further reduced and still maintain itself.  Each population has some minimal size from which it can survive in the long term.  Losses of even a few individuals from smaller populations can tip it beyond its ‘minimum viable population’ size.  The first accurate assessment of the vaquita’s abundance, which occurred in 1997, suggested there were some 567 individuals (95% Confidence Interval 177 - 1,073).  In 2008, abundance was placed around 245 individuals (95% CI 68 - 884). In 2015, surveys suggested just 59 individuals remained (95% CI 22 – 145). The primary cause for the decline is known – small-scale and industrial gillnet fishing.  These nets aren’t set to catch vaquita, but other species such as skates, mackerel, shark, and shrimp.   The answer to the vaquita’s plight is obvious; ban all gillnet fishing.

 Vaquita has been the focus of many conservation campaigns for a number of years. Image credit  SEMARNAT/Flickr  (Public Domain)

Vaquita has been the focus of many conservation campaigns for a number of years. Image credit SEMARNAT/Flickr (Public Domain)

 

Halting all gillnet fishing is not as straight-forward as some may like.  With desert surrounding the northern end of the Gulf, fishing has become an important source of revenue and food for local people, often living in poverty.  Other concerns surround gillnets set for totoaba (Totoaba macdonaldi), a large fish also endemic to the Gulf of Mexico, and also listed as critically endangered.  Despite the totoaba fishery closing in 1975, illegal fishing for the species is rife, driven by demand for totoaba bladders from China where it is believed to have medicinal value.  Bladders that make their way to Asia can fetch between U$10,000 to U$20,000 each.  With fines for being caught fishing totoaba in the region of the selling price of one or even two swim bladders (and the fishers have to actually be caught in the act to be prosecuted), the incentive for illegal fishing is strong. 

the Mexican government have introduced a number of recovery and protection measures to aid the vaquita.  In 1993 the Upper Gulf of California and Delta Biosphere Reserve were created, banning gillnetting near the Colorado River.  An additional Refuge Area, also with a gillnet ban, was created in 2005, covering the central part of the vaquita’s range.  Unfortunately with surveillance and enforcement low, and a large number of fishing vessels legally active in the areas, illegal gillnetting continued, prompting calls for stronger action.  In 2015 a new plan was introduced.  It included a two-year ban on gill-nets in a 5,000 square-mile area, increased naval-supervised enforcement, and a compensation plan for fishers who have been put out of work at a value of U$30 million a year, as well as training for legal fishers in other fishing gears.  The announcement has received some criticism.  A two-year ban is insufficient to allow vaquita to rebound, and the ban has a significant loophole; fishers can still use gill nets for (or claim to be) catching corvina, another large fish that reaches over 1 meter in length.  Based on the vaquita’s reproductive rate, 2 deaths a year will maintain the population at its current level.  For recovery, deaths need to be brought down to at least 1 individual per year, but ideally zero.  By the end of March 2016, 3 vaquita mortalities, likely from gillnets, had already been confirmed.

With predictions of vaquita extinction by 2022 unless gillnetting is completely removed, the Comité Internacional para la Recuperación de la Vaquita (CIRVA) have suggested that captive breeding, in conjunction with protection of the Vaquita’s habitat, is something that should be explored.  This controversial idea is not without its problems.  Vaquitas have never been kept in captivity, and certainly never been bred.  With so few vaquita left, removing any individuals for a breeding program may be too risky, especially if the program fails.  Which leads us back to the ‘simplest’ option.  “At this juncture”, the latest CIRVA meeting concluded, “the choice is simple and stark: either gillnetting in the Upper Gulf ends, or the vaquita becomes extinct within a very short time”.