Vaquita in decline
No species, except perhaps the baiji, has been of greater concern to the CSG over the last several decades than Mexico’s endemic Gulf of California porpoise, the vaquita (Phocoena sinus). Already by the time of its scientific discovery and formal description in 1958, the vaquita was seldom seen, difficult to observe and probably not very abundant. Its status has continued to deteriorate since then because of the unrelenting pressure from incidental mortality in fisheries.
An ongoing decline is supported by the results of a 2008 joint Mexico-US survey, recently announced by the Government of Mexico. Whilst a survey in 1997 had resulted in an estimate of 567 vaquitas (CV=51%, 95%CI 177-1073)1 the estimate of total population size in 2008, based on a combination of visual and acoustic methods, was only 245 vaquitas2 (CV=73%, 95%CI 68-884) – a discouraging result for those who have been working hard to stop the species’ decline. The 2008 estimate was 57% lower than the 1997 estimate, implying an average rate of decline of 7.6%/year, presumably due entirely to incidental mortality in gillnets and other entangling nets.
A second study3 evaluates the Mexican Government’s national vaquita conservation action plan, which includes three options for a protected area closed to gillnet fishing. The probability of success of each of the three options was estimated with a Bayesian population model, where success was defined as an increase in vaquita abundance after 10 years. If protection remains as it is currently within the existing vaquita Refuge Area, the chance of vaquita abundance increasing over that period is estimated as only 8%. If a larger area is protected as proposed in the PACE (see Vaquita page for details), the probability of success is still low at 35%. The only management option judged certain of success (>99% probability) is a protected area large enough to eliminate vaquita bycatch throughout the entire range of the species. This study clearly demonstrates that if the conservation actions remain at the present level, the vaquita is unlikely to survive.
Unfortunately, despite the considerable support given to vaquita conservation efforts by the Mexican Government, the vaquita’s decline towards extinction will continue unless all entangling nets are removed throughout the species’ range.
1 Jaramillo-Legorreta, A.M., Rojas-Bracho, L., & Gerrodette, T. (1999). A new abundance estimate for vaquitas: first step for recovery. Marine Mammal Science, 15, 957–973.
2 Gerrodette, T., Taylor, B.L., Swift, R., Rankin, S., Jaramillo-Legorreta, A. M., & Rojas-Bracho, L. (2010). A combined visual and acoustic estimate of 2008 abundance, and change in abundance since 1997, for the vaquita, Phocoena sinus. Marine Mammal Science.
3Gerrodette, T., & Rojas-Bracho, L. (in press). Estimating the success of protected areas for the vaquita, Phocoena sinus. Marine Mammal Science.