|Scientific Name:||Phocoena sinus|
|Species Authority:||Norris & McFarland, 1958|
|Red List Category & Criteria:||Critically Endangered A4d; C2a(ii) ver 3.1|
|Assessor(s):||Rojas-Bracho, L., Reeves, R.R., Jaramillo-Legorreta, A. & Taylor, B.L.|
|Reviewer(s):||Perrin, W.F., Hammond, P.S. & Crespo, E.A. (Cetacean Red List Authority)|
The vaquita qualifies for listing as Critically Endangered based on criteria A4d and C2a(ii).
The generation time for the vaquita is estimated as 10 years (Rojas-Bracho and Taylor 1999, Taylor and Rojas-Bracho 1999), therefore three generations is approximately 30 years.
Criterion A4d: Given what is known about fishing history in the northern Gulf of California and the vaquita's vulnerability to entanglement in gillnets, it is reasonable to assume that the porpoise population has been declining since the 1940s when gillnet fisheries became widespread in the region. The best estimate of total population size is from 1997: 567 (95% CI: 177, 1,073) (Jaramillo-Legorreta et al. 1999). The estimated annual level of mortality in the early 1990s for one of the three main fishing communities, based on reports from onboard observers (Method 1) and those observer reports combined with information from interviews with fishermen (Method 2), was 84 (95% CI: 14, 155) (Method 1) or 39 (95% CI: 14, 93) (Method 2) (Rojas-Bracho and Taylor 1999, D'Agrosa et al. 2000). Using the 1997 abundance estimate, the range of bycatch estimates for a single community in the early 1990s, and plausible potential rates of population increase for phocoenids, Rojas-Bracho and Taylor (1999) estimated that the vaquita population was declining rapidly, possibly by as much as 15% per year. Using the lower of their plausible decline rates (0.05), the population size would be reduced by more than 80% over three generations (i.e., 30 years), including both the past and the future (Rojas-Bracho and Taylor 1999). The cause of the reduction (incidental mortality in fisheries) has not ceased and may even have increased over the last 10 years based on fishing effort (ca. 1,000 gillnet boats might operate in vaquita habitat each year; Rojas-Bracho et al. 2006).
Criterion C2a(ii): The mature and reproductively active component of the census population is estimated as 0.55 (Woodley and Read 1991), or 311 in 1997. Given the inferred decline in abundance due to fishery bycatch during the nine years since 1997 (possibly at a rate of 0.05 to 0.15/yr according to Taylor and Rojas-Bracho 1999), there are now plausibly far fewer than 250 mature individuals (criterion C). From available data on fishery activities (types and effort) and vaquita bycatch rate, a continuing decline in number of mature individuals is projected and inferred (C2). It is assumed that the species population is not divided into subpopulations and therefore 100% of mature individuals are in a single population (C2aii).
|Previously published Red List assessments:|
|Range Description:||The vaquita is known to occur only in the northern Gulf of California, Mexico, mainly north of 30º45'N and west of 114º20'W (Gerrodette et al. 1995). The so-called "core area" consists of about 2,500 km² centred at Rocas Consag, some 40 km northeast of the town of San Felipe, Baja California. This core area straddles the southern boundary of the Upper Gulf of California and California River Delta Biosphere Reserve. There is no evidence to indicate that the vaquita's overall range has changed in historic times.|
Endemic to upper quarter of Gulf of California, extent of occurrence (EOO) >2,000 km², area of occupancy (AOO) (core area) approx. 2,000 km².
Native:Mexico (Baja California, Sonora)
|FAO Marine Fishing Areas:|
Pacific – eastern central
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||The most recent estimate of total population size comes from a shipboard line transect survey in 1997 that was stratified to provide relatively intensive coverage of the core area but that also sampled adjacent areas to the south, east and north, including the shallow marginal bays and the even shallower Colorado River delta. Although imprecise because of variable sighting rates and other factors, the estimate of 567 (95% CI 177 to 1,073) was a great improvement on previous estimates and stands as the best currently available.|
There is no immediate means of estimating trend, so it is necessary to impute the direction and rate of population change by reference to a population model laden with assumptions.
Naturally rare (Taylor and Rojas-Bracho 1999) and very difficult to detect and count (cryptic) (Gerrodette et al. 1995). No population subdivision is known or suspected, i.e. no subpopulations, but also no fragmentation. Most recent estimate of total population size (1997 shipboard line transect survey): 567 (95% CI 177 to 1,073) (Jaramillo-Legorreta et al. 1999).
Given the difficulty of sampling the vaquita population, generation time and percent mature (i.e., capable of reproduction) can only be estimated crudely and by analogy with the life history and population biology of the better-studied harbour porpoise (Phocoena phocoena). Thus reasonable default values for porpoises (phocoenids) would be 10 years and 55%, respectively.
Ongoing decline inferred from available information on abundance and bycatch rate. Even an unrealistically optimistic scenario - high end of 95% CI for population size (1,073), lower of two estimates of annual bycatch mortality for a single fishing port (39 porpoises) - indicates likely decline (Rojas-Bracho and Taylor 1999).
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||The vaquita is a marine species that lives in a relatively shallow (<40 m), turbid and dynamic environment (Vidal 1995, Rojas-Bracho and Jaramillo-Legorreta 2002). Vaquitas feed on a variety of demersal or benthic fishes, squids and crustaceans. They have been observed singly and in small groups of up to 8 or 10 individuals (mean = 2), but many such groups can be loosely aggregated over several km².|
|Major Threat(s):||Mortality in gillnets of various mesh size has long been recognized as the most serious and immediate threat to the vaquita's survival (Vidal 1993, 1995; Reeves and Leatherwood 1994; IWC 1995:87, 167; Rojas-Bracho and Taylor 1999; Rojas-Bracho et al. 2006). The only available estimates of the vaquita bycatch rate are 39 (using one method) and 84 (using a different method) animals killed per year by boats from a single port (D'Agrosa et al. 2000). This alone would represent 7 or 15%, respectively, of the estimated total population size (Rojas-Bracho and Jaramillo-Legorreta 2002). Other potential threats that have been suggested but that appear not to be significant risk factors at present include inbreeding depression, pesticide exposure and ecological changes as a result of reduced flow from the Colorado River (Taylor and Rojas-Bracho 1999). The last of these may be important in the long term and deserves investigation.|
Only approximately half of the "core area" of vaquita distribution falls within the Upper Gulf of California and Colorado River Delta Biosphere Reserve, which was created in 1993. Moreover, the nuclear zone of the Reserve, which is the only area where all fishing is prohibited, appears to be grossly mismatched with vaquita distribution as no sightings of vaquitas were made inside this zone during the two large-scale systematic surveys in the 1990s (Gerrodette et al. 1995, Jaramillo-Legorreta 1999).
An International Committee for the Recovery of the Vaquita (CIRVA) was established in 1997 and has developed recommendations including: immediate prohibition of large-mesh gillnets throughout the species' known range, followed in sequence by bans on medium- and small-mesh gillnets; exclusion of gillnets and trawls within an enlarged biosphere reserve; and improved enforcement of fishing regulations in the northern Gulf generally. Considerable attention has also been given to development of less harmful fishing methods, alternative income-generating activities for fishing communities, and community-based education and awareness (Rojas-Bracho et al. 2006).
On 29 December 2005 the Mexican Ministry of Environment declared a Vaquita Refuge that contains within its borders approximately 80% of all verified vaquita sighting positions. In the same decree, the State Governments of Sonora and Baja California were offered $(US)1 million to compensate affected fishermen. The results of this action cannot yet be evaluated.
It is listed on CITES Appendix I.
|Citation:||Rojas-Bracho, L., Reeves, R.R., Jaramillo-Legorreta, A. & Taylor, B.L. 2008. Phocoena sinus. The IUCN Red List of Threatened Species 2008: e.T17028A6735464.Downloaded on 26 August 2016.|