Sotalia guianensis (Van
English: Guiana dolphin; Costero
French: Sotalia côtier
Sotalia guianensis © Würtz-Artescienza (see "links")
The appearance of the Guiana dolphin resembles that of a smaller
bottlenose dolphin. It is light grey to bluish-grey on the back
and pinkish to light grey on the belly, with a distinct boundary
between the mouth gape and the flipper's leading edge. On the sides,
there is a lighter area between the flippers and the dorsal fin.
The dorsal fin is triangular and may be slightly hooked at the tip.
The beak is moderately slender and long. The Guiana dolphin is significantly
larger than the tucuxi. Body size reaches 210-220 cm and body mass
80 kg (Flores and da Silva, 2009).
Dolphins of the genus Sotalia are found along the Caribbean
and Atlantic coasts of Central and South America and in the Amazon
River and most of its tributaries. Until recently, the taxonomy
of these dolphins was unresolved. Although five species were described
in the late 1800s, only one species was recognized prior to 2007
fluviatilis) with two ecotypes or subspecies, the coastal
subspecies (Sotalia fluviatilis guianensis) and the riverine
subspecies (Sotalia fluviatilis fluviatilis) (Rice, 1998
and refs. therein; Culik, 2004).
Distribution of Sotalia guianensis: coasts
of north-eastern South America and eastern
Central America (Reeves et al. 2008; © IUCN; enlarge
Recent morphometric analyses, as well as mitochondrial
DNA analysis, suggested recognition of each subspecies as separate
species (e.g. Furtado, 1999). Caballero et al. (2007) and Cunha
et al (2005) reviewed the history of the classification of this
genus. Caballero et al. (2007) presented new genetic evidence from
ten nuclear and three mitochondrial genes as well as evidence from
previous studies supporting the elevation of each subspecies to
the species level under the Genealogical Lineage Concordance Species
Concept and the criterion of irreversible divergence. The authors
proposed the common name 'costero' for the coastal species, Sotalia
guianensis (Van Beneden 1864), and accept the previously proposed
'tucuxi' dolphin, Sotalia fluviatilis (Gervais, 1853), for
the riverine species. More recently, "Guiana dolphin"
has been used for Sotalia guianensis (Flores and da Silva,
S. guianensis (P.-J. van Bénéden, 1864) is
found in inshore coastal waters, estuaries, and the lower reaches
of rivers along the western Atlantic from Nicaragua (14°35'S)
south to Floreanópolis, Santa Catarina, Brazil (27°35'S)
(Flores and daSilva, 2009). This subspecies includes Sotalia
brasiliensis E. Van Bénéden, 1875 (Rice, 1998
and references therein). In a recent paper Carr and Bonde (2000)
extended the known range to the northwest in northeastern Nicaragua,
north of the mouth of the Layasiksa River, west side of Waunta Lagoon
(13°40'N) where one individual was positively identified.
3. Population size
The species appears to be relatively abundant throughout its range.
Numerous estimates exist of relative abundance in small areas, such
as minimum number sighted, encounter rate, and estimates of minimum
density (IWC, 2000). The following summary moves from north to south.
Edwards and Schnell (2001) found that in the Cayos Miskito Reserve,
Nicaragua, 49 Sotalia inhabited the portions of the Reserve
studied. Mean overall density was 0.6 individuals/km², with
slightly lower densities in lagoons (0.5 ind/km²).Bossenecker
(1978, in da Silva and Best, 1994) estimated 100-400 dolphins near
the mouth of the Magdalena River in Colombia, and noted that they
were abundant in the Gulf of Cispata, near San Antero (Colombia).
In Suriname, they were described as "rather common" in
the mouths of the larger rivers, and in Guyana they were reported
as "frequent" in the lower reaches and mouth of the Essequibo
Sotalia were reported to be common in the Baia de Guanabara
(Rio de Janeiro), by Geise (1991, in da Silva and Best, 1994) who
estimated the population at 418 individuals in about 109 groups.
Geise (1989, in da Silva and Best, 1994) estimated the total number
of individuals for the area around Cananéia Island to be
2,829. In Sepetiba Bay, Southeast Brazil, a population density of
2.79 dolphins/km² and a population of 1,269 individuals (CI=739-2,196)
were estimated. Density and abundance were similar for the entrance
and interior of the Bay (Flach et al. 2008).
4. Biology and Behaviour
Habitat: Marine Sotalia show a preference for shallow
protected estuarine waters or bays. In the Baia de Guanabara (Rio
de Janeiro), they prefer the deeper channels (25 m depth) and avoid
areas with less than about 6m of water. Where the rivers that feed
such areas are large enough, dolphins may penetrate up to 130 km
or more upriver; however the species identity of these dolphins
is still uncertain. The major restriction to the south seems to
be low sea-surface temperature (Reyes, 1991 and refs. therein) of
the Malvinas current. They may range as far as 70 km offshore, e.g.
in the Abrolhos Archipelago (Flores and daSilva, 2009).
Sightings of Sotalia groups in the Cayos Miskito Reserve, Nicaragua
indicates that some areas were preferred. In coastal areas Sotalia
were sighted most often within 100m of shore and the animals were
seldom observed in more than 5m of water (Edwards and Schnell, 2001).
Schooling: According to da Silva and Best (1994) Guiana
dolphins occur in groups of as many as 30 individuals, with a mode
of 2 per group in the Baia de Guanabara and Cananéia. Group
size varies in these two areas according to the time of day and
type of activity. Borobia (1984) and Geise (1984, 1989, both in
da Silva and Best, 1994) reported that in the marine form, calves
are usually observed in small groups of three (one calf and two
adults) or four (two calves and two adults). Azevedo et al. (2005)
investigated group characteristics in Guanabara Bay, south-eastern
Brazil. Group size ranged between 1 - 40 individuals and groups
of 2 -10 were most common. There was no variation in group size
between seasons, but nursery groups were twice as large than non-calf
groups. Flores and daSilva (2009) reported that Guiana dolphins
do not associate with bottlenose dolphins in Brazilian waters.
Edwards and Schnell (2001) found a mean group size of 3 in the Cayos
Miskito Reserve, Nicaragua.
Reproduction: Males reach sexual maturity at 7 years and
at body lengths estimated at 170-175 cm. Females mature at 5-8 years
of age and at body lengths of 164-169 cm. The reproductive cycle
is estimated at 2 years, with no marked seasonality in ovulation
or timing of birth. Gestation is about 12 months, fetal growth rate
was 9 cm/month, and length at birth is estimated at 92.2 cm. Females
older than 25 years have senescent ovaries (Rosas and Monteiro-Filho,
Food: Marine Sotalia from southeast Brazil feed on a diet
of pelagic clupeids (Trichurus lepturus and Pellona barroweri),
demersal sciaenids (Cynoscio spp., Porichthys porosissimus,
Micropogonias furnieri) and neritic cephalopods (Loligo
spp. and Lolliguncula brevis). In Santa Catarina these dolphins
are known to feed on the anchovies which are abundant in this area
(da Silva and Best, 1994). Back-calculation of prey lengths indicated
that fish ranged from 1.2 to106.9 cm and cephalopods from 3.4 to
22.2 cm in mantle length (Di Beneditto and Arruda Remos, 2004).
Demersal fishes usually associated with estuarine sandy bottoms
were the main prey items. Sciaenid fishes that produce relatively
loud sounds by swimbladder muscular contraction were observed as
common prey items. The dolphins also prey on shrimps (Penaeus
schmitii and P. paulensis; Penaeidae) (De oliveira Santos
et al. 2002).
General patterns: Marine Sotalia may penetrate up
to 130 km or more upriver. The marine form probably also has a defined
home range, although the area covered may be large because of the
distances between one estuary or protected bay and another (Reyes,
1991). Geise (1989) and Andrade et al. (1987, both in da Silva and
Best, 1994) observed individuals identified by natural marks in
the same area for over 1 year. Home ranges are probably among the
smallest for small cetaceans, with 15 km² in southern Brazil
and up to 265 km² in another location.
Movement patterns vary among cold and warm seasons in the temperate
regions, whereas in warmer waters no seasonal movements are known
(Flores and daSilva 2009). Furthermore, Guiana dolphins show strong
site fidelity. In Guanabara Bay, southeastern Brazil, which is surrounded
by a metropolitan complex and is the most degraded area of the species'
distribution, individuals were seen for 4.5 consecutive years, with
a range of 1 to 8 years, and calves remained in the area beyond
sexual maturity (Azevedo et al. 2004).
Diurnal rhythms: An apparent diurnal behaviour rhythm has
been observed in whereby Guiana dolphins entered the Bahía
de Guanabara between 06:00 and 08:00h and left between 13:00h and
18:00h but were rarely seen entering and leaving the bay on the
same day (12% of the observations). A similar behaviour was reported
for S. guianensis in the Cananéia region (da Silva and Best,
1994 and references therein; Geise et al. 1999).
At Enseada do Mucuripe in Fortaleza, Brazil, the distribution of
sightings and displacement routes of Sotalia suggested preferential
uses of the sites Praia Mansa and Praia de Iracema at different
times, suggesting movement patterns between resting and feeding
areas. Highest and lowest frequencies of sightings at Praia de Iracema
occurred respectively in the first and fourth quarters of the day.
The higest frequencies happened at low tide (Oliveira et al. 1995).
Direct catches: There are no records of past or recent commercial
fisheries for Sotalia (IWC, 2000). On the coast of Brazil they may
occasionally be killed for use as bait for sharks or shrimp traps
or for human consumption, although the extent of this practice is
Incidental catches: Modern fishing practices and the greatly
increased intensity of fishing in both the marine and freshwater
habitats are the greatest direct threats to the species. Guiana
dolphins are easily captured in monofilament gill nets as well as
in shrimp and fish traps and seine nets. Beltran (1998, in IWC,
2000) recorded 938 animals taken in drift nets from the port of
Arapiranga during the summer of 1996 and a further 125 taken during
the winter. These data were collected by interviewing fishermen
in the port after trips and collecting carcasses. The IWC sub-committee
on small cetaceans expressed its concern about the magnitude of
these catches. More recently, Monteiro-Neto et al. (2004) estimated
that approximately 90 Guiana dolphins are killed every year in the
passive gill net fisheries along the Brazilian coast. In the metropolitan
area of Fortaleza, the capital of Ceara State, 32 bycaught animals
were recorded. The use of pingers in fishing nets may assist in
the mitigation of entanglements.
Habitat degradation: Another potential threat to Sotalia
spp., in both riverine and coastal environments, is the damming
of rivers for hydroelectric projects, with future plans for up to
200 such dams in series along many of the main Amazon tributaries.
Where such dams are built on rivers that empty directly into the
sea, the altered flux of freshwater may affect both the primary
and secondary productivity in the estuaries and reduce the feeding
potential of these areas for Guiana dolphins (da Silva and Best,
1994, Jefferson et al. 1993).
Pollution: Pollution from industrial and agricultural activities
may be considered a threat both directly, through the destruction
of habitat, or indirectly, through contamination of the food chain.
Large harbours like the Baia de Guanabara (Rio de Janiero) and Santos
(São Paulo) are extremely polluted with effluent, including
heavy metals, posing a serious potential threat. The continued use
of insecticides containing substances banned elsewhere is common
in South America (da Silva and Best, 1994 and ref. therein). However,
Guiana dolphins from the Cananeia Estuary, an important biological
area on the southeast coast of Brazil, had lower organochlorine
concentrations in their blubber than small cetaceans from developed
areas elsewhere in the world, although the estuary is known to have
been impacted by both chlorinated pesticides and polychlorinated
biphenyls (PCBs)(Yogui et al. 2003).
Mercury is used in the refining of fluvial gold and then, like
the pesticides, probably enters the aquatic food chain of the rivers
and coasts. Mercury and selenium were found in the livers of two
Sotalia from Suriname (da Silva and Best, 1994 and ref. therein).
The detection of Cd, Hg and Pb in tissue samples of S. guianensis
off the coast of Ceara, Brazil, indicated that heavy metals are
locally available in the waterand bioaccumulation may be occurring
through the food web. Contamination levels were not considered critical,
but they could be related to Ceara's growing industrial development.
The associated risks of pollution outfalls may pose a threat to
marine organisms in a near future, especially for top predators
such as the Guiana dolphin (Monteiro-Neto et al. 2003).
Exploration for oil in the offshore regions of Brazil, Venezuela
and Colombia may not pose a direct threat to S. guianensis. Nevertheless,
the apparent dependence of this dolphin on estuaries means that
an oil spill near such an area could contaminate the food chain
and affect local populations (da Silva and Best, 1994 and ref. therein).
Range states (Reeves et al. 2008):
Brazil, Colombia, Ecuador, French Guiana, Guyana, Nicaragua, Panama,
Peru, Suriname and Venezuela.
Sotalia sp. is listed in Appendix II of CITES and S.
guinanensis is listed in Appendix II of CMS. The species is
listed as "Data Deficient" by the IUCN.
On the Atlantic coast of South America, large rivers are geographical
limits for countries along the coast. Because of the estuarine preference
of tucuxis in the area, it is likely that the dolphins move between
some of these countries (Reyes, 1991, and refs. therein). According
to Monteiro et al. (2000) the small number of individuals in conjunction
with long gestation and nursing periods, suggest that an increased
mortality due to dolphin-fisheries interactions could severely impact
local populations. The IWC sub-committee (IWC, 2000) recognised
that incidental catches of S. guianensis are widespread.
Little information exists regarding marine Sotalia populations,
and in many areas, such as the lower Orinoco, it is not clear which
species is present (IWC, 2000, and refs. therein).
The IWC sub-committee on small cetaceans (2000) recommended:
- that research should be directed towards detecting trends in abundance
by making repeatable and statistically rigorous estimates of density
in a range of regions and habitats,
- that information be collected to allow evaluation of the relative
levels of incidental mortality associated with different fishing
- that research be directed to determine which species of Sotalia
occurs in areas such as the Orinoco and Amazon estuaries.
· Azevedo AF, Lailson-Brito JJr, Cunha HA, van Sluys M A
(2004) A note on site fidelity of marine tucuxis (Sotalia fluviatilis)
in Guanabara Bay, southeastern Brazil
· Azevedo AF, Viana SC, Oliveira AM, Van Sluys M (2005) Group
characteristics of marine tucuxis (Sotalia fluviatilis)
(Cetacea: Delphinidae) in Guanbara Bay, south-eastern Brazil. J
Mar Biol Assoc UK 85: 209-212
· Caballero S, Trujillo F, Vianna JA, Barrios-Garrido H,
Montiel MG, Beltran-Pedreros S, Marmontel M, Santos MC, Rossi-Santos
M, Santos FR, Baker CS (2007) Taxonomic status of the genus Sotalia:
species level ranking for 'tucuxi' (Sotalia fluviatilis)
and 'costero' (Sotalia guianensis) dolphins. Mar Mamm Sci
· Carr T, Bonde RK (2000) Tucuxi (Sotalia fluviatilis)
occurs in Nicaragua, 800km north of its previously known range.
Mar Mamm Sci 16: 447-452.
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behaviour, migration and threats. UNEP/CMS Secretariat. Marine Mammal
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© Boris Culik (2010) Odontocetes.
The toothed whales: "Sotalia guianensis". UNEP/CMS
Secretariat, Bonn, Germany. http://www.cms.int/reports/small_cetaceans/index.htm
© Illustrations by Maurizio Würtz, Artescienza.
© Maps by IUCN.