Sotalia fluviatilis (Gervais
and Deville, 1853)
Spanish: Delfín del Amazonas
French: Sotalie fluviale
Sotalia fluviatilis © Würtz-Artescienza (see "links")
The appearance of the tucuxi resembles that of a smaller bottlenose
dolphin. The tucuxi 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. Body size reaches 152 cm and the
tucuxi is thus much smaller than its close relative, the Guiana
dolphin and reaches a body mass of 55 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
(Sotalia 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).
Provisional distribution map of Sotalia fluviatilis:
rivers of north-eastern South 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 accepted the previously
proposed 'tucuxi' dolphin, Sotalia fluviatilis (Gervais,
1853), for the riverine species. More recently, the common name
"Guiana dolphin" has been used for the marine species
(Flores and da Silva, 2009).
S. fluviatilis occurs in the main tributaries of the Amazon/Solimoes
River basin with records in all three types of water that occur
in this region. The tucuxi does not occur in the Beni/Mamoré
river basin in Bolivia nor in the upper Rio Negro. In the Orinoco,
the species presence is controversial, a stretch of rapids and water
falls blocking movements (Flores and da Silva 2009).
3. Population size
The species appears to be relatively abundant throughout its range
(Flores and da Silva 2009). Numerous estimates exist of relative
abundance in small areas, such as minimum number sighted, encounter
rate, and estimates of minimum density (IWC, 2000):
In the Amazon drainage area, an average density of approximately
1.1 dolphins per km of river was estimated between Manaus and Tefé
in the Solimoes river. In the Iquitos area, Kasuya and Kajihara
(1974, in da Silva and Best, 1994) recorded 62 Sotalia during
36 hr of observations. Further upstream, Sotalia were frequently
encountered in the Samiria river and its tributary the Santa Helena
river. They are also common in Colombia in the Loretoyacu River,
and the Tarapoto River at the El Correo Lake system and in the lower
reaches of the Orinoco River (da Silva and Best, 1994 and refs.
therein). Mean density along the margins of main rivers in the central
Amazon, Brasil (1,320 km of survey strip) was 3,2 individuals per
km². More that 54% f the individuals occurred within 50 m of
the edge of rivers and channels (Martin et al. 2004).
Vidal et al. (1997) conducted a boat survey in 1993 to estimate
the abundance of the tucuxi along ca. 120 km of the Amazon River
bordering Colombia, Peru, and Brazil. They estimated that there
are 409 Sotalia in the study area. Sotalia density
was highest in lakes (8.6 per km²), followed by areas along
main banks (2.8 per km²) and around islands (2.0 per km²).
These are among the highest densities measured to date for any cetacean.
In Peru's Pacaya-Samiria National Reserve. encounter rates were
within the range of encounter rates for these dolphins elsewhere
in South America. Riverine dolphin populations appear to be relatively
healthy. Studies indicate that population numbers in the Samiria
System have been stable over the last 10 years (McGuire, 2002).
4. Biology and Behaviour
Habitat: Tucuxis inhabit all types of water ("whitewater",
"clearwater", and "blackwater" rivers) of the
Amazon region, so physical factors such as visibility and pH appear
not to affect their distribution directly. They are found in the
main channels of rivers as well as in larger lakes where access
is not limited by a narrow or shallow channel. They generally do
not enter the flooded forest. Rapids and fast-moving turbulent water
are also avoided. Sotalia show a distinct preference for junctions
of rivers and channels (da Silva and Best, 1994 and references therein).
Martin et al. (2004) confirmed that in western Brazil highest densities
occurred near the margin, and were lowest in the center of rivers.
Tucuxi prefer areas with diminished current and where two channels
join, the most preferred habitat type being where a sediment-rich
white water channel meets one carrying acidic black water; the resultant
mixing produces particularly productive, and obviously attractive,
conditions for dolphins.
Photo: Paulo André Flores @ Sotalia
Dolphin Project (see "links")
McGuire and Henningsen (2007) used photo-identification to examine
range, rate of movement, and site fidelity of S. fluviatilis
in Peru's Pacaya-Samiria Reserve from 1991 to 2000. Maximum range
for Sotalia was 130 km, with a greatest rates of movement
of 56 km/d. Encounter rates were highest in confluences, intermediate
in lakes, and lowest in rivers. In general, encounter rates in rivers
and lakes did not differ among seasons. During low water, tucuxi
persisted longer in the confluences throughout the sampling day,
and occurred in higher densities than in any other season; the reverse
pattern was observed during high water (McGuire, 2002).
Schooling: According to da Silva and Best (1994) the tucuxi
and Guiana dolphin have a similar social structure. The riverine
form occurs in groups of one to six individuals in 55% of the observations.
Groups of more than nine animals are seen on rare occasions. Group
composition is unknown. Two groups that were captured consisted
of a female with a male calf, and the third of a pregnant female
with an immature female (da Silva and Best, 1994). Vidal et al.
(1997) reported overall mean group size of 3.9 individuals in the
upper Amazon river. In rivers and lakes of Peru's Pacaya-Samiria
Reserve, tucuxis were seen most often as singles or pairs. Significant
seasonal differences in group size were not detected (McGuire, 2002).
Reproduction: In Brazil, calving in the riverine form apparently
occurs primarily during the low water period, September to November
(Jefferson et al. 1993). Gestation is estimated at 11 months (Flores
and da Silva, 2009).
Food: In the Amazon region, tucuxis prey upon at least 28
species of fish belonging to 11 families. The characoid family Curimatidae
was represented in 52%, Sciaenidae in 39% and siluriforms in 54%
of the stomachs analysed (n = 29) . In the dry season fish become
concentrated in the main water bodies and thus are more vulnerable
to predation. During the flood period many of these fish enter the
floodplain to feed, but Sotalia usually do not enter this
habitat (da Silva and Best, 1994). Da Silva and Best (1996) found
that competition between man and dolphin for commercial fish is
still minimal in the Central Amazon. Dietary analysis has shown
that only 43% of 53 identified prey-species are of commercial value
and that the dolphins generally prey on size-classes of fish below
those of commercial interest.
General patterns: The principal limiting factor in the Amazon
is the presence of rapids and small channels, where manoeuvrability
would be restricted. The large seasonal fluctuation in river levels
(10m) influences the distribution of tucuxis: they enter lake systems
during periods of high water but will leave these as the waters
recede, thus avoiding entrapment in lakes that are too small or
shallow. Animals may occur during the whole year in the same area.
Two tagged individuals in the Amazon were found within 5 km of the
tagging site up to 1 year later (da Silva and Best, 1994 and references
therein; Jefferson et al. 1993). It is therefore possible that tucuxis
have a limited home range, but the area of such a range is unknown
Two types of travelling were observed: slow directional movement
and faster swimming, including porpoising, usually in a single direction
(Jefferson et al. 1993). The tucuxi is present in rivers of the
Amazon region that cross territories of such countries as Brazil,
Colombia, Ecuador and Peru. It definitely crosses international
boundaries in areas such as Leticia, as Amazon river dolphins do
(Reyes, 1991, and refs. therein).
Diurnal rhythms: An apparent diurnal behaviour rhythm has
been observed in the Amazon, where more Sotalia were seen between
09:00 and 10:00h than at any other time (da Silva, unpublished data).
There was a marked movement into lakes from rivers in the early
morning before about 09:00h, and again in the late afternoon from
about 16:00 to 18:00h.
Major threats for the tucuxi are related to human fishing activity,
and include entanglement in fishing gear and possibly poisoning
to reduce net damage and predation on fish. Potential threats include
boat strikes, oil spills, water and noise pollution, and overfishing
of prey (McGuire 2002).
Direct catches: There are no records of past or recent commercial
fisheries for Sotalia spp. (IWC, 2000). Tucuxis have been protected
by the superstitions of fishermen from Colombia to southern Brazil
as well as in the Amazon. (Jefferson, 1993; da Silva and Best, 1994
and refs. therein). Interviews with fishermen in the boats, in the
fishmarket and in the shops supposedly selling dolphin products
were conducted in an attempt to quantify the overall incidental
kill attributed to commercial fisheries operations. The results
showed that in the Central Amazon dolphin catches are incidental
and only a very small number of these carcasses are used for commercial
purposes (da Silva and Best, 1996).
Incidental catches: Modern fishing practices and the greatly
increased intensity of fishing are the greatest direct threats to
the species. The tucuxi is easily captured in monofilament gill
nets as well as in shrimp and fish traps and seine nets. Analysis
of the type of fishing gear associated with the mortality of 34
animals from the central Amazon revealed that 74% were caught in
gill nets and 15% in seine nets. They apparently do not steal fish
from nets as do Inia
in the Amazon, but as they consume 14 of the 30 species of fish
most exploited by man in the Amazon, incidental captures during
fishing are frequent (da Silva and Best, 1994 and refs. therein;
da Silva and Best, 1996). Martin et al. (2004) showed that tucuxis
selectively occur in areas known to be favoured for gill net deployment
by local fishermen, which may explain why entanglement is apparently
a common cause of mortality.
Habitat degradation: Another potential threat to riverine
Sotalia, 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. At the very least, such dams would
interrupt gene flow between Sotalia populations, creating
isolated groups between dams. Furthermore, most of the migratory
fish on which Sotalia feed would become extinct in the reservoirs,
and the potential suitability of nonmigratory fish for the diet
of Sotalia is unknown (da Silva and Best, 1994, Jefferson et al.
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.
The continued use of insecticides containing substances banned elsewhere
is common in South America. Mercury is used in the refining of fluvial
gold and then, like the pesticides, probably enters the aquatic
food chain of the rivers (da Silva and Best, 1994 and ref. therein).
Range states (mod from Reeves et al. 2008):
Brazil; Colombia; Ecuador; Peru; Venezuela
According to Monteiro et al. (2000) the small number of individuals
in conjunction with long gestation and nursing periods suggests
that an increased mortality due to dolphin-fisheries interactions
could severely impact local populations. The IWC sub-committee on
small cetaceans (IWC, 2000) recognised that incidental catches of
tucuxi are widespread.
Sotalia fluviatilis is listed in Appendix I of CITES and
in Appendix II of CMS. The species is listed as "Data Deficient"
by the IUCN.
The tucuxi is abundant and widely distributed in the central Amazon,
but there are no estimates of total population size. It is vulnerable
to the same threats that apply to Inia, including fisheries entanglement,
habitat deterioration and fragmentation of populations by dam construction.
The large numbers of animals taken as incidental catches in the
Amazon estuary are a cause for concern, though it is not yet clear
which form of Sotalia these represent (IWC, 2000, and refs. therein).
The IWC sub-committee on small cetaceans (2000) recommends:
- 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 of the tucuxi associated with different
- that research be directed to determine which form of tucuxi occurs
in areas such as the Orinoco and Amazon estuaries.
National legislation specifically protects the tucuxi in Brazil,
Peru, and Colombia. The species is indirectly protected in Ecuador,
Venezuela, Guyana, and French Guiana (Reyes, 1991, and refs. therein).
· 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
· Culik BM (2004) Review of small cetaceans: distribution,
behaviour, migration and threats. UNEP/CMS Secretariat. Marine Mammal
Action plan/ regional Seas Reports and Studies no. 177. 343 pp.
· Cunha HA, Silva VMF, Lailson-Brito J, Santos MCO, Flores
PAC, Martin AR, Azevedo AF, Fragoso ABL, Zanelatto RC, Sole-Cava
AM (2005) Riverine and marine ecotypes of Sotalia dolphins are different
species. Mar Biol 148: 449-457.
· Flores PAC, Dasilva VMF (2009) Tucuxi and Guiana Dolphin
- Sotalia fluviatilis and S. guianensis. In: Encyclopedia
of marine mammals, 2nd Ed. (Perrin WF, Würsig B, Thewissen
JGM, eds.) Academic Press, Amsterdam, pp. 1188-1192.
· Furtado NM (1999) Molecular systematics and population
genetics of marine vertebrates from Brazil. Dissertation Abstracts
International Part B: Science and Engineering 60: 463:463.
· IWC (2000) Annex K: Report of the sub-committee on small
cetaceans. IWC, Cambridge, 2000.
· Jefferson TA, Leatherwood S, Webber MA (1993) FAO Species
identification guide. Marine mammals of the world. UNEP/FAO, Rome,
· Martin AR, Silva VMFda, Salmon DL (2004) Riverine habitat
preferences of botos (Inia geoffrensis) and tucuxis (Sotalia
fluviatilis) in the Central Amazon. Mar Mamm Sci 20: 189-200
· McGuire TL (2002) Distribution and abundance of river dolphins
in the Peruvian Amazon. Diss Abst Int Pt A - Hum & Soc Sci 63:1403.
· McGuire TL, Henningsen T (2007) Movement patterns and site
fidelity of river dolphins (Inia geoffrensis and Sotalia
fluviatilis) in the Peruvian Amazon as determined by photo-identification.
Aquat Mamm 33: 359-367
· Monteiro NC, Alves JTT, Avila FJC, Campos AA, Costa AF,
Silva CPN, Furtado NMAA (2000) Impact of fisheries on the tucuxi
(Sotalia fluviatilis) and rough-toothed dolphin (Steno
bredanensis) populations off Ceara state, northeastern Brazil.
Aquat Mamm 26: 49-56.
· Reeves RR, Crespo EA, Dans, Jefferson TA, Karczmarski L,
Laidre K, O'Corry-Crowe G, Pedraza S, Rojas-Bracho L, Secchi,ER,
Slooten E, Smith BD, Wang JY, Zhou K (2008). Sotalia fluviatilis.
In: IUCN 2009. IUCN Red List of Threatened Species. Version 2009.2.
· Reyes JC (1991) The conservation of small cetaceans: a
review. Report prepared for the Secretariat of the Convention on
the Conservation of Migratory Species of Wild Animals. UNEP/CMS
· Rice DW (1998) Marine mammals of the world: systematics
and distribution. Society for Marine Mammalogy, Spec Publ 4, Lawrence,
· Silva VMFda, Best RC (1994) Tucuxi - Sotalia fluviatilis
(Gervais 1853) In: Handbook of marine mammals (Ridgway SH, Harrison
SR, eds.) Vol. 5: The first book of dolphins. Academic Press, London,
· Silva VMFda, Best RC (1996) Freshwater dolphin/fisheries
interaction in the Central Amazon (Brazil). Amazoniana 14: 165-175.
· Vidal O, Barlow J, Hurtado L A, Torre J, Cendon P, Ojeda
Z (1997) Distribution and abundance of the Amazon river dolphin
(Inia geoffrensis) and the Tucuxi (Sotalia fluviatilis)
in the Upper Amazon river. Mar Mamm Sci 13: 427-445.
© Boris Culik (2010) Odontocetes.
The toothed whales: "Sotalia fluviatilis". UNEP/CMS
Secretariat, Bonn, Germany. http://www.cms.int/reports/small_cetaceans/index.htm
© Illustrations by Maurizio Würtz, Artescienza.
© Maps by IUCN.