Phocoena sinus Norris
& McFarland, 1958
English: Vaquita, Gulf of California porpoise
French: Marsouin du Golfe de Californie
Phocoena. sinus © Wurtz-Artescienza (see
The vaquita is one of the smallest odontocetes (only P.p.
minor is smaller). Mean length for females is only 140 cm.
The flippers are proportionately larger than in other phocoenids
and the dorsal fin is taller and more falcate. The pigmentation
is a dark grey cape, pale lateral field and white ventral field.
There are large black eye rings and lip patches. The skull is smaller
and the cranial rostrum is shorter and broader than in other members
of the genus. The vaquita is the most endangered odontocete species
in the world (Rojas-Bracho and Jaramillo-Legorreta, 2009).
The vaquita is endemic to the head of the Golfo de California,
from Puertecitos, Baja California Norte, north and east to Puerto
Peñasco, Sonora. Reports from farther south have never been
confirmed (Brownell et al., 1986). Vaquitas mainly live north of
30°45'N and west of 114°20'W. Their 'core area' consists
of about 2,235 km² (the most restricted distribution of any
marine mammal species) centered between Rocas Consag and San Felipe
Bay, close to Baja California State coast (Jaramillo-Legorreta et
al. 1999; Rojas-Bracho and Jaramillo-Legorreta, 2009).
Distribution of Phocoena sinus: murky
coastal waters in the northern quarter of the
Gulf of California. This is the most restricted range of any marine
(Rojas-Bracho et al. 2008; © IUCN; enlarge
3. Population size
Jaramillo-Legorreta et al. (1999) conducted a line-transect survey
in 1997 and the total population size was estimated to be 567 (95%
CI = 177-1073) animals. Note the wide confidence limits: this dated
estimate is, until today, the most recent population estimate (Rojas-Bracho
and Jaramillo-Legoretta, 2009). The continued increase of fishing
effort in the area leads to an estimate of the current population
size at 40% of its 1997 level, i.e. in the range of 71 - 430 individuals
(Rojas-Bracho and Jaramillo-Legoretta, 2009). A recent estimate
of the number of vaquitas remaining is based on the abundance estimate
for 1997, the mortality rate in fishing nets in 1993, the estimated
level of fishing from 1993 to 2007, the maximum population growth
rate for porpoises and a standard population model for population
growth. The currently remaining population was estimated at 150
animals (Jaramillo-Legorreta et al, 2007). The IWC in its 2008 meeting
confirmed that the current vaquita population size was considered
by most, including the Mexican Government, to be no more than 150
animals. This represents an extraordinarily rapid decline of approximately
75% in a decade. If this scale of fishery mortality continues, it
will likely result in the effective extinction of the species in
a maximum of 5 years and probably less (IWC, 2008). The species
is not extinct yet and there is still hope: an expedition in 2008
reported 13 sightings (T. Jefferson, 2010, pers. comm. and Jefferson
et al. 2010 in press).
4. Biology and Behaviour
Habitat: The vaquita lives in a shallow basin, and is rarely
seen in water much deeper than 30 m (Vidal, 1995). Other characteristics
of its habitat are strong tidal mixing, convection processes and
high primary and secondary productivity (Rojas-Bracho and Jaramillo-Legorreta,
2002). Silber (1990) reported 51 sightings in water depths of 13.5-37
m, and most of these sightings were 11-25 km from shore. Water visibility
ranged from 0.9 m to 12 m.
Behaviour: The vaquita appears to swim and feed in a leisurely
manner, but is elusive and will avoid boats of any kind. It rises
to breathe with a slow, forward-rolling movement that barely disturbs
the surface of the water, and then disappears quickly, often for
a long time (Carwardine, 1995).
Schooling: Like other phocoenids, P. sinus occurs singly or in small
groups. In 58 sightings, 91% comprised 1-3 individuals, with a mean
group size of 1.9 and a range of 1-7 (Silber, 1990). Loose aggregations
of vaquitas in which they were dispersed as single individuals or
as small subgroups (from 2-4 , greatest number 8-10) spread over
several hundred square metres were also reported (Vidal et al. 1999
and refs. therein).
Reproduction: Most calving apparently occurs in the spring.
Gestation is probably 10-11 months. Maximum observed life span was
21 years (Hohn et al. 1996).
Food: All of the 21 fish species found in vaquita stomachs
can be classified as demersal and/or benthic species inhabiting
relatively shallow water in the upper Gulf of California, and it
appears that the vaquita is a rather non-selective feeder on small
fish, squid and crustaceans in this zone. (Vidal et al. 1999; Rojas-Bracho
and Jaramillo-Legoretta, 2009).
An analysis of all available sightings led Silber and Norris (1991)
to suggest that vaquitas occupy the northern Gulf year-round. This
has more recently been confirmed with the aid of acoustic surveys
(Jaramillo-Legoreta et al. 2005).
Incidental catch: The most important human-induced problem
affecting this species is incidental mortality in fishing gear.
Vaquitas used to be incidentally captured in gillnet fishing operations
(legal, illegal and experimental) for totoaba (Totoaba macdonaldi),
an endemic and endangered large seabass-like fish. After the ban
of totoaba fishery, vaquitas continue being captured in gillnets
set on sharks, rays, mackerels (Scomberomorus sierra and
S. concolor), chano (Micropogonias megalops) (a "croaker"),
and shrimp (Penaeus spp.). Between March 1985 and January
1994, 76 vaquitas were confirmed ( to have been) killed incidentally
in totoaba gill nets. All the porpoises taken in shrimp fisheries
were referred to as "very small", probably calves or juveniles.
Considering the large number (ca. 500) of shrimp boats operating
in the upper Gulf of California at the beginning of each typical
shrimping season, this fishery poses an additional threat to vaquitas,
particularly younger ones (Vidal et al. 1999, and refs. therein).
Vaquita continue to be caught in small-mesh gillnet fisheries throughout
much of the range. D'Agrosa et al. (2000) monitored fishing effort
and incidental vaquita mortality in the upper Gulf of California
from January 1993 to January 1995 to study the magnitude and causes
of the incidental take. Of those factors studied, including net
mesh size, soaktime, and geographic area, none contributed significantly
to the incidental mortality rate of the vaquita, implying that the
principal cause of mortality is fishing with gillnets per se. The
total estimated incidental mortality caused by the fleet of El Golfo
de Santa Clara was 39 vaquitas per year, which is over 17% of the
most recent population estimate. Progress towards reducing entanglement
has been slow in spite of efforts to phase out gill nets in the
vaquita's core range, and the development of schemes involving compensation
for fishermen (Rojas-Bracho et al. 2006).
The boundaries of the Upper Gulf of California and Colorado River
Delta Biosphere Reserve of 1993 did not correspond well with the
distribution of vaquitas. The shallow water north of the town of
San Felipe was found to have a higher density of animals than had
been indicated by previous surveys (Jaramillo-Legorreta et al. 1999).
In December 2005, the Mexican Ministry of Environment therefore
declared a Vaquita Refuge that contains within its borders the positions
of approximately 80% of verified vaquita sightings. In the same
decree, the state governments of Sonora and Baja California were
offered $1 million to compensate affected fishermen (Rojas-Bracho
et al. 2006). However although this money "ostensibly paid
regional fishermen not to fish, they instead went to buy new boats
and motors." Very recently, the Mexican government has gone
one step further, forbidding any kind of fishing operations inside
the Vaquita Refuge (Platt, 2009).
Habitat degradation: The international committee for the
recovery of the vaquita (CIRVA) agreed that in the long term, changes
in vaquita habitat due to reduction of the Colorado river flow as
a result of dam construction and water withdrawal upstream is a
matter of concern and needs to be investigated (Rojas-Bracho and
Pollution: Concerns have been expressed about organochlorine
pollutants in the food web. However relatively low concentrations
of total DDT, alpha-BHC, and PCBs were found in blubber samples
analysed in 1985, and values were lower than those reported for
various odontocetes and marine birds from most other areas (Vidal
et al. 1999, and refs. therein).
Range states (Rojas-Bracho et al. 2008) : Mexico.
Phocoena sinus is listed in CITES Appendix I and II . The
World Wide Fund for Nature (WWF) considers the vaquita as one of
the most endangered small cetaceans world wide (WWF, 2009). A 2007
study estimated that at least 100 vaquita are necessary to preserve
the species' genetic diversity. With presumably only 150 porpoises
left today, every vaquita counts (Platt, 2009).
It is considered "Critically Endangered" by the IUCN
(Rojas-Bracho et al. 2008) based on the fact that the population
may be declining by as much as 15% per year or more than 80% in
three generations. The cause of the mortality has not ceased and
may even have increased. Current size of the mature population is
estimated at less than 250 mature individuals in a single population.
Because the vaquita only occurs in Mexican waters, the framework
of CMS does not apply.
As pointed out by Rosel and Reeves (2000), genetic and demographic
consequences associated with very small population size can result
in extinction even when effective measures are in place to protect
the animals and their habitat. This is explained by low genetic
variation, genetic drift and inbreeding and lower fitness. Low levels
of variation in the Major Histocompatibility Complex warn about
a high susceptibility to novel pathogens and diseases in vaquita
(Munguia-Vega et al. 2007).
According to Rojas and Taylor (1999), mortality resulting from
fisheries bycatch poses the highest risk and primary conservation
efforts should be directed towards immediate elimination of incidental
fishery mortality. One of the possibilities could be acoustic deterrents
and their compulsory use in gillnet fisheries, provided that protected
areas located nearby remain net-free (Culik et al. 2001). However,
CIRVA and the IWC did not recommend the use of pingers, as these
would require a baseline scientific study and financial support
to fishermen. Furthermore, pingers could dislocate the vaquita from
its small core area without being expected to reduce by-catch to
zero. Therefore, a total ban on fisheries, as pronounced by the
Mexican government, was be preferred (L Rojas-Bracho, pers. comm..
The International Committee for the Recovery of the Vaquita (CIRVA)
- a reduction of vaquita by-catch to zero, by removing gill-net
fisheries in three stages, starting with large mesh sizes,
- enforcement of fishing regulations,
- development and testing of alternative fishing gear,
- expansion of the southern limit of the Upper Gulf of California
and Colorado River Delta Biosphere Reserve to include the entire
range of the vaquita,
- banning of trawlers from the entire biosphere reserve,
- investigation of the abundance and seasonal movement of vaquitas
via acoustic surveys,
- the design and development of public education and awareness programmes,
-investigation and development of strategies to offset economic
hardships imposed by such regulations (Rojas-Bracho and Jaramillo-Legoretta,
D'Agrosa et al. (2000) further recommend:
- a maximum annual allowable mortality limit of vaquitas, and
- mandatory observer coverage of all boats fishing within the Upper
Gulf of California and Colorado River Delta Biosphere Reserve.
Recently, the President of Mexico announced a Conservation Programme
for Endangered Species, and the vaquita is listed among the top
five species. Should this initiative fail the vaquita is most likely
doomed to extinction in the near future (Rojas-Bracho and Jaramillo-Legoretta,
Acknowledgement: We are grateful to Lorenzo Rojas Bracho for
kindly reviewing this account.
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© Illustrations by Maurizio Würtz, Artescienza.
© Maps by IUCN.