The vaquita is the smallest porpoise, and the smallest cetacean. It lives only in the Gulf of California (Sea of Cortez), where latest abundance estimates point to just 30 animals left (as of November 2016). The original population in the 1930s was estimated to be around 5,000 individuals strong. In the 1990s, that number had declined to about 700. But in recent years, the population has declined at a dramatic rate. Between 2011 and 2016, the population has declined by 90%.
Gill-nets and by-catch
The single most serious thread to the vaquita, and the cause for its rapid decline, is the use of gill-nets in the vaquita habitat.
A gill-net is a wall of netting that hangs in the water column. The mesh is designed so that fish can get their heads through, but not the rest of their bodies. As they struggle to free themselves, they get entangled with their gills. Gill-nets are very effective and used around the world, but often lead to large amounts of by-catch and pose a threat to other marine animals, such as sea turtles, seals and sea lions and cetaceans like the vaquita. If a vaquita gets entangled, it only has minutes to free itself. Most animals drown, and those that escape often do so with severe injuries.
The use of gill-nets in the vaquita habitat is currently banned throughout the vaquita’s range. However, illegal fishing continues, targeting the totoaba for the Chinese market.
The totoaba is a large species of fish which, like the vaquita, is listed on the IUCN Red List as “critically endangered”. This illegal fishing activity is quickly driving this species to extinction while also severely accelerating the decline of the vaquita as the animals get entangled as by-catch and drown.
Reduced flow of the Colorado River: The Colorado River feeds into the Sea of Cortez, and a reduced inflow of nutrients is indeed believed to have degraded the vaquita habitat. However, scientists found that nutrient concentrations are still well above limits at which primary productivity would be impacted, and the vaquita have enough fish to feed on.
Contamination due to pollution: Pollution was also believed to play a role. However, contamination levels in the Sea of Cortez are also well below levels where they would present a risk to the vaquita.
References and Further Reading
- Gerrodette, Tim ; Taylor, Barbara L. ; Swift, René ; Rankin, Shannon ; Jaramillo-Legorreta, Armando M. ; Rojas-Bracho, Lorenzo (2010). A combined visual and acoustic estimate of 2008 abundance, and change in abundance since 1997, for the vaquita, Phocoena sinus. Marine Mammal Science.
- Cantú-Guzmán, Juan Carlos ; Olivera-Bonilla, Alejandro ; Sánchez-Saldaña, María Elena (2015). A history (1990-2015) of mismanaging the vaquita into extinction - A Mexican NGO's perspective. Journal of Marine Animals and Their Ecology.
- Jaramillo-Legorreta, Armando M. ; Rojas-Bracho, Lorenzo ; Gerrodette, Tim (1999). A new abundance estimate for vaquitas: First step for recovery. Marine Mammal Sci.
- JARAMILLO-LEGORRETA, A. ; ROJAS-BRACHO, L. ; URBAN, J. (2005). A review of acoustic surveys and conservations actions for the vaquita. Scientific Committee Meeting Documents.
- Castellazzi, Giovanni ; Krysl, Petr ; Rojas, Lorenzo ; Cranford, Ted W. (2012). Assessment of the effect of natural and anthropogenic aquatic noise on vaquita (Phocoena sinus) through a numerical simulation. Advances in Experimental Medicine and Biology.
- LORENZO ROJAS-BRACHO ; RANDALL R. REEVES ; ARMANDO JARAMILLO-LEGORRETA (2006). Conservation of the vaquita Phocoena sinus. Mammal Review.
- Environmental Investigation Agency (2016). Dual extinction: The illegal trade in the endangered totoaba and its impact on the critically endangered vaquita. Briefing to the 66th Standing Committee of CITES.