Ecology of Commerson´s Dolphins - Whale and Dolphin Conservation

Ecology of Commerson´s Dolphins
WDCS Argentina researchers Miguel Iniguez and Vanesa Tossenberger
are carrying out a long-term study of this southern-hemisphere species.
Commerson´s dolphin, Cephalorhynchus
commersonii, is distributed in the coastal waters
of South America south of 41ºS. It is also found
in the waters of Islas Malvinas (Falkland Islands)
and the Kerguelen Islands (Goodall et al.,
1988a; Leatherwood et al., 1988a; Iñíguez, 1991;
Rice, 1998). Its restricted distribution makes it
particularly vulnerable to coastal gillnets (Iñíguez
et al. 2003).
In January 1999, 12 dead Commerson´s dolphins
were reported in the Río Gallegos area and nine
showed evidence of gillnet entanglement. This
event led the local Secretariat of the Environment
(Subsecretaría de Medio Ambiente of Santa Cruz
Province - SMASC) to request further study on C.
commersonii in the area, and following that request
Iñíguez and colleagues began monitoring beach cast
dolphins along the coast for signs of net entanglement
(Iñíguez et al. 2003). Between January 1999 and
February 2000, near 70 Commerson´s dolphins were
found dead along the coast near La Angelina and Ría
Gallegos. Out of these, many dolphins were in an
advanced state of decomposition and the probability of
entanglement could not be determined, but net marks
were observed in around 40 animals (Iñíguez et al.
2003). During the 2000/2001 season, the mortality of
Commerson´s dolphins could not be systematically
© Miguel Iniguez
Location: - Southern Argentina
Species: - Commerson´s Dolphin (Cephalorhynchus
commersonii)
Lead Researcher: -Miguel Iñiguez
Team: - Marta Hevia, Cecilia Gasparrou and Vanesa
Tossenberger
Commerson’s dolphins are incredibly easy to identify at sea due to their dictinve black
and white colourations.
monitored but it appears that high capture rates
continued in the Ría Gallegos and La Angelina areas.
Between January and February 2001, around 30
“[Commerson’s]
restricted
distribution makes
it particularly
vulnerable to
coastal gillnets.”
Commerson´s dolphins incidentally caught in gillnets in
this area were reported to the monitoring team (Iñíguez
et al. 2003).
Despite its vulnerability to fishing activities and
its low reproductive potential (Iñíguez et al., 2003),
there is a lack of basic information (e.g. total bycatch, abundance, stock structure) to allow a proper
assessment of the species’ status under the IUCN Red
List criteria and it is currently listed as “Data Deficient”
(IUCN, 2006). In Santa Cruz Province, the provincial
law Nº2582 declared the Commerson´s dolphin a
Provincial Natural Monument in July 2001 to protect
the local resident populations.
© Nicola Hodgins
Reason for the project
The general objective of this project is to make a
systematic study of the species’ different aspects
including distribution range, distribution patterns,
genetic diversity and population size within Santa
Cruz Province, southern Patagonia. This information is
important to assess the impact of human activities, if
any, on these cetaceans in order to design appropriate
management plans for these species and its habitat.
Project Aims/Objectives
●● To estimate Commerson´s dolphins status in
Commersons dolphins are very acrobatic animals and enjoy bow-riding, breaching,
and are highly sociable, often found in large groups.
Santa Cruz province
●● To develop more conservational programs for the
species in Argentina.
●● To contribute with valuable information from a very
poor known seacoast of the province on Commerson’s
dolphins threats.
1
© Nicola Hodgins
entanglements) from the southernmost subpopulation
(Ría Gallegos) and from beachcast specimens as well
as biopsy samples from free-swimming dolphins (using
the scrape-sampling technique developed by Cipriano
et al) from Puerto Santa Cruz, Puerto San Julián and
Puerto Deseado.
Conservation initiatives
WDCS Argentina researchers Vanesa Tossenberger, Marta Hevia and Cecilia Gasparrou spend
the austral summer every year in Patagonia studying the Commerson’s dolphins.
Ad libitum and Animal Group Focal methodology
will be used. Surveys are made from vessels. The
information to be taken from a vessel will be in a 5.2m
length with 55 HP outboard engines boat, according to
the methodology of focal group (Altmann, 1974; Mann,
1999).
We are planning to continue the work with GIS
software. Records of Commerson’s dolphins are
plotted to determine the use of habitat at different
months, tide and time at Bahía San Julián.
Data analysis consists in studying the proportion
diversity and haplotype distribution from control region
sequencing, and this year the priority will be given to
the assessment of evidence for genetic differentiation
across this geographic area from microsatellite
polymorphism frequencies and distributions.
The study will focus on the potential for depletion of
the subpopulation in the Ría Gallegos area by high and
continuing incidental catches, in terms of decreased
genetic diversity and statistically significant genetic
differentiation relative to the northern areas. Since
2004, work has been initiated on tissue samples from
beachcast specimens (probably derived from gill net-
Future Plans
We will need to collect more information, because it
is important to assess the impact of human activities, if
any, on these cetaceans in order to design appropriate
management plans for these species and its habitat.
More management scheme will be providing as
well as data for the conservation of the species.
© Nicola Hodgins
Methodology
The fear that we have is that, the population that most
of the dead dolphins came from will also be too small
to sustain such a large number of deaths. To stop this
critical situation, the team has been working closely
with the relevant provincial authorities and fishermen
to find solutions, whilst initiating further research to
determine resident population size as well as the
increase of the knowledge of the species.
Another action to be take is to continue working
with the Provincial Government, advising them on
wording for new protection initiatives, such as it
was, in July 2001, when a provincial law to protect
the Commerson´s dolphin was established and was
declared by the Province of Santa Cruz’s Chamber of
Deputy
“The study will
focus on the
potential for
depletion of the
subpopulation in
the Ría Gallegos”
of time sighted related to sampling effort. Tissue/
biological samples will be collecting if animals are
found.
Genetics
The proposed project is the continuation of the ongoing assessment of genetic diversity of Commerson’s
dolphin subpopulations along the southern Argentina
coastline, from Puerto Deseado in the north to Ría
Gallegos in the south (project already supported by
WDCS). This field season will also be dedicated to the
collection of further biopsy samples, and tissues from
stranded animals if found, on Santa Cruz Province
to widen Commerson’s dolphin genetic data with the
intention of deepening the ongoing analysis. Analyses
will include evaluation of mitochondrial DNA sequence
2
Males and females of the species can be distinguished by the black patch on the
underside of the belly; males have a “teardrop” shape, females a “horseshoe” shape.
© WDCS
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