Pontoporia blainvillei (Gervais
and d'Orbigny, 1844)
English: La Plata dolphin
French: Dauphin de la Plata
Pontoporia blainvillei ©Wurtz-Artescienza
The Franciscana is the only one of the four river dolphin species
living in the marine environment and the sole member of its family.
It is one of the smallest dolphins and has an extremely long and
narrow beak and a bulky head. Its colour is brownish to dark grey
above and lighter on the flanks and belly. Females are larger than
males, ranging between 137-177 cm as opposed to 121-158 cm in males.
Females weigh up to 53 kg and males reach 43 kg (Crespo, 2009).
The franciscana is restricted to coastal and estuarine central
Atlantic waters of South America. The northern limit of the distribution
is Itaúnas (18°25'S), Espirito Santo State, Brazil. In
the south, the range extends to Golfo San Matías (41°10'S),
in northern Patagonia, Argentina (Crespo, 2009).
The sighting of a single individual in Golfo Nuevo, Valdez Peninsula,
is considered exceptional and this should not be considered the
southern distribution limit for franciscana (Crespo, 2000).
Geographic distribution of Pontoporia blainvillei
on the east coast of South America
(Reeves et al. , 2008; © IUCN; enlarge
Data on mtDNA, morphometrics, parasitology and population parameters
all together provide evidence for splitting the species into four
provisional "Franciscana Management Areas": two inhabiting
coastal waters of Brazil (FMA I - coastal waters of Espírito
Santo and Rio de Janeiro states; FMA II - São Paulo, Paraná
and Santa Catarina states); FMA III occurring in Rio Grande do Sul
State (southern Brazil) and Uruguay, and FMA IV in coastal Argentine
waters (Secchi et al., 2003a). This population fragmentation, together
with the relatively low genetic variability, suggests that the franciscana
dolphin is a potentially vulnerable species, which may require management
efforts to ensure its preservation.
3. Population size
Abundance estimates for the franciscana in its natural environment
are difficult to obtain due to the great difficulty in sighting
it at sea. Current estimates are presented from north to south of
In Babitonga Bay, on the northern coast of Santa Catarina State,
southern Brazil, a total of 561 individuals were observed between
1996 and 2001 (Cremer and Simoes-Lopez, 2005). A subsequent estimate
in the same area between 2000 and 2003 gave an estimated population
size of only 50 animals. The difference was not explained but is
likely due to methodological discrepancies between the two studies
rather than population decline. Observed density was 0.32 individuals
/ km². Density estimates evaluated in the sub-areas where franciscanas
occurred resulted in a density of 0.46 individuals / km² (Cremer
and Simoes-Lopez, 2008).
A first abundance estimate for the coastal waters of Rio Grande
do Sul State (southern Brazil) and Uruguay stems from 1996 data,
resulting in an overall estimate of 42,078 franciscanas (95% CI:
33,047-53,542) (Secchi et al., 2001). However, this may be too optimistic:
during the corresponding an aerial survey 34 franciscanas (in 29
groups) were recorded leading to a mean density estimate of 0.657
individuals/km² for the study area (435 km²) after applying
a correction factor for submerged dolphins. This corresponds to
an estimated abundance of 286 franciscanas (95% CI: 225 to 364)
in the study area, which represents only 0.7 % of the distribution
of the proposed population (Secchi et al., 2001).
Extrapolating the 1996 density to the area of the Rio Grande do
Sul coast, however, from shoreline up to the 30m isobath (ca. 24,315
km2), the abundance would be around 15,975 animals (Secchi, 2010a).
A subsequent abundance estimate for this region was provided based
on a line transect aerial survey carried out in February 2004 (Danilewicz
et al., 2009). The surveyed area was much larger than in 1996 and
comprised 13,341 km2 and at least 20 transect lines. The corrected
density was 0.51 franciscanas/km2 , which gives an extrapolated
abundance of 12,400 for the entire area of 24,315 km2. The difference
between the 1996 and 2004 estimates was not viewed as a population
decline and is attributed to methodological reasons (Secchi, 2010a).
However, declining stranding rates in Rio Grande do Sul in the face
of substantially increasing fishing effort in the 1990's was attributed
to a decline in franciscana abundance (Pinedo and Polacheck, 1999).
The most recent abundance estimate conducted in Argentine waters
stems from 2003-2004. A total of 101 Franciscanas were observed
in 71 sightings. In northern areas density was estimated at 0.106
individual/km2. Density was lower in southern areas and depths greater
than the 30-m isobath (0.05/km2). A correction factor for submerged
dolphins was applied to density and then extrapolated to the strip
between the coastline and the 30-m isobath. From the number of animals
observed and after extrapolation, abundance in the northern area
was estimated at 8,279 (4,904-13,960) individuals, while in the
southern area it was estimated at 5,896 (1,928-17,999) individuals
(Crespo et al. 2009).
The assumed distributional areas significantly influence abundance
estimates: while the 30 m and even the 50 m isobath is assumed to
be the offshore limit for the distribution of the species (Crespo,
2009), in the North of Rio de Janeiro State, 90% of sightings were
obtained within 5 nm from shore, in waters only up to 15 m deep
(DiBeneditto and Ramos, 2001). Therefore, the Secchi (2010a) estimate
that total abundance could be up to 42,000 franciscanas for the
whole Rio Grande do Sul and Uruguay coastal waters, and the Crespo
(2009) estimate of 15,000 in Argentina, both considering the 30-m
isobath as the offshore limit, may be optimistic. The IWC Scientific
Committee concluded, after reviewing the methods and limitations
of franciscana surveys through 2003-2004, that it was not appropriate
to consider them as providing minimum estimates of abundance (IWC
4. Biology and Behaviour
Habitat: The species shows a pronounced preference for relatively
shallow, turbid waters (Pinedo et al., 1989; Secchi and Ott, 2000),
a coastal marine ecosystem characterized by continental runoffs
with a high discharge of high-nutrient river flows (e.g. Lagoa dos
Patos, Rio de la Plata) (Crespo, 2009). In the north of Rio de Janeiro
State sightings were recorded in all seasons and 90% of them were
obtained up to 5 nm (8 km) from shore, in waters up to 15 m deep
(DiBeneditto and Ramos, 2001). Franciscana sightings from shore-based
stations and vessels at Bahia Anegada, Argentina, near Rio Colorado
were at a mean distance from shore of only 3.2 km (Bordino et al
1999). A positive correlation between the surface water temperature
and the presence of franciscana was observed. Tide and depth also
influenced behaviour. The animals usually enter the channels during
high tide. Other authors state that maximum depth of sightings was
of 25 meters measured by nautical charts (Bordino et al. 1999) or
even as deep as 50 m in Argentinean waters (Crespo, 2009).
Schooling: Herd size is small, ranging from 2 to 15 individuals
(DiBeneditto and Ramos, 2001; Crespo, 2009). In Babitonga Bay, southern
Brazil, up to 59.5% of the groups consisted of over four individuals
and the average group size was seven (Cremer and Simoes-Lopez, 2005).
In other areas, calves were recorded during spring and summer and
only one calf was observed per group. In Argentina, the behaviour
showed a seasonal pattern with co-operative feeding and travelling
activities increasing during winter. Co-operative feeding increased
during flood tide, while travelling decreased. The behavioural ecology
of the franciscana appears similar to that of other coastal and
river dolphins (Bordino et al. 1999 and Bordino, in Crespo, 2000).
Franciscana dolphins may travel in kin groups which might include,
besides mothers with their calves or juvenile offspring, the fathers
of the youngest group members. All four individuals from the presumed
social group shared the same mitochondrial haplotype, suggesting
that the social unit might be matrilineally structured (Valsecchi
and Zanellatto, 2003).
Photo: Bruce Hayward
Reproduction: In the North of Rio de Janeiro State, calving
occurs throughout the year, with no seasonal pattern. Females attain
sexual maturity at 3 years and 130.0 cm in length and males at 2
years and 115.0 cm (DiBeneditto and Ramos, 2001). In Babitonga Bay,
southern Brazil, calves were present in 30.4% of the observations,
during all seasons (Cremer and Simoes-Lopez, 2005). Danilewicz (in
Crespo, 2000) presented reproduction data from the northern coast
of Rio Grande do Sul based on 22 females and 9 males and reported
that births in this region occur during October to January with
a water temperature over 20°C. He suggested that mating occurs
in January and February based on observations of ovaries with traces
of recent ovulations. He found lactating females between October
and January and that births coincide with the periods of higher
abundances of main prey. All the individuals were sexually mature
at the age of 3 years. No pregnant females were found nursing at
the same time though the sample was small. Crespo (2002) estimates
longevity at 15 y for males and 21 y for females.
Food: Analyses of stomach contents indicate that franciscanas
consume a wide variety of mainly bottom-dwelling fish species (Brownell,
1989). Sciaenid and engraulid fish comprise the main prey items.
Squid and shrimp are also reported. Animals examined in Uruguay
had eaten fish species common in coastal waters of the mouth of
the La Plata River (Reyes, 1991).In the North of Rio de Janeiro
State, Franciscana preferentially feed on the teleosts Stellifer
sp., Anchoa filifera, Pellona harroweri and Isopisthus
parvipinnis, measuring up to 10cm of length, and on the cephalopods
Loligo sanpaulensis and L. plei (DiBeneditto and Ramos,
2001). Diet preferences may vary regionally and between years, making
franciscana a bioindicators of changes in fish stocks. In Brazilian
and Uruguayan waters, a few species accounted for the majority of
prey consumed. In Uruguay, the most important species (based on
estimated biomass) were C. striatus during winter, spring,
and summer, and T. lepturus during autumn. In Brazil, four
sciaenids, P. brasiliensis, C. striatus, M. ancylodon, M. jurnieri,
and the squid (L. sanpaulensis) accounted for 87.7% of the
estimated biomass and 89.7% of the total individuals ingested; 76%
of these were C. striatus (Brownell, 1989 and refs. therein).
Reyes (1991) stated that apart from the documented intrusion into
the La Plata River in search of prey, there is no additional information
on movements of this species.
In the North of Rio de Janeiro State, sightings were recorded in
all seasons and incidental captures were recorded throughout the
year (DiBeneditto and Ramos, 2001). Results of parasitological analyses
suggest that P. blainvillei might be sedentary, at least in spring-early
summer, hence showing separate stocks, despite the relative closeness
between localities (Aznar et al. 1995).
In Rio Grande do Sul, Southern Brazil, strandings occur year round,
with peaks during spring, from September to December. However, this
is the main period when the artisanal bottom- tending gillnet fisheries
are active. However, in winter, franciscana were found at a significantly
greater mean distance from shore than during summer(Pinedo and Polacheck,1999).
This may explain why franciscana groups along the Mar del Plata
coast and in Bahia Anegada were sighted mostly in spring and summer
(Bastida; Bordino and Iniguez, both in Crespo, 2000).
Incidental catch: Combination of information on bycatch
from fleet monitoring programs and interviews along the species'
range (Secchi, 2010b) resulted in an annual bycatch estimate of
about 110 (min: 44; max:176) franciscanas for FMA I; 279 (min: 63;
max: 497) for FMA II; 1,245 (min: 562; max: 1,778) for FMA III and;
405 (min: 241; max: 567) for FMA IV (Ott et al., 2002 and Secchi
et al., 2003b). Incidental mortality is largely related to fisheries
targeting elasmobranchs and sciaenids (Crespo et al. 2007) and similar
by-catch estimates are given in Crespo (2009). However, the highest
estimates of abundance cannot sustain the lowest estimates of incidental
catches (Crespo, 2002; 2009), showing that there is a mismatch.
Unfortunately no recent by-catch estimates are available and data
generally stem from dated reports, when population size might have
been higher and/or fisheries efforts were higher. The estimated
total mortality throughout the range could be in the order of 1,200-1,800
per year (Crespo, 2009) and Reeves et al. (2008) estimate that up
to 2,900 animals could be incidentally caught in fisheries per year
and that even this figure might be underestimated.
However, field data indicate that by-catch rates may be rather variable:
in the north of Rio de Janeiro State, the annual catch per unit
effort (CPUE) values varied from 0.2-1.8 dolphins per gillnet fishing
effort (DiBeneditto and Ramos, 2001). Along the coasts of Uruguay,
a decrease in mortality was observed since the 1970's. The highest
value for the 1990's was 235 individuals in 1992-93, while during
1998, only 23 individuals were recorded. The suggested reason for
the decline of the catch include the drop in fish stocks. At present,
this fishery is not profitable. The fisheries using nets with larger
mesh, the most harmful for franciscana (32-34 and 20-22mm) have
reduced their effort and nets with smaller mesh (12-14mm) are being
used at present. Uruguayan legislation protecting the marine fauna
including franciscana (Law 9481 and Decrees 26 1/78, 586/79 and
565/81) is being enforced (Praderi, in Crespo, 2000).
Similarly relatively low catch values were recorded in the 1990's
from Paraná, Brasil (Zanelatto, in Crespo, 2000). Monzón
(in Crespo, 2000) comments that since 1991 there was no information
on franciscana mortality in the area of Necochea (Buenos Aires Province).
She noted a significant decrease in gillnet fishing effort from
50 vessels in the early 1990s to only one at present. Coastal fishing
in small communities (for example Santa Teresita), however, results
in the highest mortality values of the region.
A promising double blind experiment conducted in an artisanal gillnet
fishery in Argentina shows the effectiveness of acoustic deterrents
(pingers) at reducing by-catch. As opposed to 45 dolphins being
caught in silent nets, only 7 were caught in the active pinger nets.
However, sea-lions (Otaria flavescens) increasingly damaged
the fish in active pinger nets over the course of the experiment
suggesting the use of higher pinger frequencies to avoid a "dinner
bell" (Bordino et al. 2002).
To conclude, several analyses indicate a high probability that the
franciscana population is decreasing. Results indicate that current
levels of entanglement mortality cannot be sustained and that protective
measures are urgently needed (e.g. Kinas, 2002). About 3.5%-5.6%
of the stock may be removed each year by the fishery, i.e. over
the maximum 2% recommended by the International Whaling Commission
which may not be sustainable. Higher densities in coastal areas
make Franciscanas more vulnerable to coastal fishing camps, with
increased mortality in recent years (Crespo et al. 2009).
Pollution: According to Brownell (1989) ratios of DDT to
DDE in the blubber of franciscana were at least an order of magnitude
higher than in small cetaceans from California. This indicates the
use of pesticides, which entered the coastal marine ecosystems in
southern Brazil and Uruguay. Wide ranges of organochlorine residues
were more recently determined in the blubber of franciscana incidentally
caught along Brazilian coastal waters (Kajiwara et al. 2004). Concentrations
of DDTs and PCBs were the highest, followed by CHLs, TCPMOH, dieldrin,
TCPMe, heptachlor epoxide, HCB, and HCHs. Unexpectedly, significant
pollution of PCBs, DDTs, TCPMe, and TCPMOH were observed in cetaceans
from Brazil, implying the occurrence of local sources comparable
to those in the Northern Hemisphere, probably by high industrialization
in Brazil (Kajiwara et al. 2004). A large proportion of the distributional
range is subject to pollution from several sources, especially agricultural
land use and heavy industries between Sao Paolo in Brazil and Bahía
Blanca in Argentina (Crespo, 2002).
Habitat degradation: Heavy coastal traffic and pollution
from industrial development represent potential threats for the
habitat of the franciscana. Recent widespread deforestation and
agricultural cultivation occur in many of the basins draining into
the Rio de La Plata system, particularly in southeastern Brazil.
Fish species of commercial value normally constitute the diet of
franciscanas, so an increase in the fishing effort for these fish
could reduce available food for the dolphins (Reyes, 1991 and references
therein). The coastal zone frequented by the franciscana is also
intensively used for boat traffic, tourism, and artisanal and industrial
fishing operations (Crespo, 2002; 2009).
Range states (Reeves et al. 2008) :
Argentina (Buenos Aires, Chubut, Rio Negro); Brazil (Espírito
Santo, Paraná, Rio de Janeiro, Rio Grande do Sul, Santa Catarina,
São Paulo); Uruguay
The Franciscana is included in Appendices I and II of CMS. The
species is listed in Appendix II of CITES. The species is listed
as "Vulnerable" by the IUCN (Reeves et al. 2008) based
on a suspected 30% and ongoing decline over three generations which
is feared to increase due to fishery expansion and lack of mitigating
measures. The World Wide Fund for Nature (WWF) considers Pontoporia
blainvillei as one of the most endangered small cetaceans world
wide (WWF, 2009).
Participants in a CMS meeting held in 2000 (Crespo, 2000) considered
it essential to prepare an integrated conservation plan which includes
work with the pertinent authorities, fishing communities, public
awareness, environmental education and legislation review. It was
suggested that Argentina, Brazil and Uruguay consider the possibility
of developing a Memoradum of Understanding for franciscana
conservation within the framework of the CMS. Participants agreed
to consider franciscana as the most endangered small cetacean in
the South-western Atlantic. The endemism of franciscana and its
restricted distributional area are important conditions for the
species besides the high impact of human activities. Main concerns
for franciscana conservation are the higher rates of incidental
mortality in artisanal fisheries throughout the area of distribution
as well as chlorinated hydrocarbon and heavy-metal spills as a result
of the industrial and agricultural activities in the coastal zone.
Open questions related to the franciscana which were identified
in 1991 and 2000 and still apply today are: 1) area-dependent rate
of incidental mortality in fishing activities and 2) unknown population/stock
status and size (Reyes, 1991; Crespo 2000).
Acknowledgement: We are grateful to Eduardo Secchi for kindly
reviewing this species summary.
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© Illustrations by Maurizio Würtz, Artescienza.
© Maps by IUCN.