Land
based survey for whales and dolphins off Arraial do Cabo, Eastern coast
of Rio de Janeiro, Brazil
July
- December 2002 (unterstützt durch yaqu pacha)
|
Research
team
Salvatore
Siciliano, Lucas B. Hassel, Andréa Venturotti, Fagner Augusto de
Magalhães |
Grupo de Estudos de Mamíferos
Marinhos da Região dos Lagos (GEMM-Lagos)
Laboratório de Ecologia,
Departamento de Endemias Samuel Pessoa
Escola Nacional de Saúde
Pública/Fiocruz - Rua Leopoldo Bulhões, 1480 - Manguinhos
- Rio de Janeiro, RJ 21041-210 Brazil - Phone: +55-21-2598-2666 - Fax:
+55-21-2598-2610 |
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Introduction |
 |
The Cabo Frio upwelling
system (23°S, 42°W) is an anomaly on the west side of the Atlantic
Ocean on the coast of Rio de Janeiro State, Brazil. The area has geographic
and oceanographic characteristics which promotes upwelling of nutrient
enriched waters and leads an improvement of fishery activities.
The coastal waters of Arraial
do Cabo were designated as a marine protected area in January 1997. The
present report describes the field activities of Grupo de Estudos de Mamíferos
Aquáticos da Região dos Lagos - GEMM-Lagos conducted in Arraial
do Cabo, Rio de Janeiro, during the annual counting of whales migrating
north to their breeding grounds off Northeastern Brazil.
Field activities were conducted
from July to December 2002, with higher effort during July when four interns
participated. |
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Material
and Method
This work was conducted
from the top of the 74m high Pontal do Atalaia, a prominent headland located
on the eastern coast of Rio de Janeiro state, Brazil, using the point transect
method. Daily sightings of whales and dolphins were recorded from 05:30AM
to 06:30PM using reticule binoculars (TASCO OffShore 54S) and a spotting
scope (Bushnell Spacemaster WA 22x67mm). Wind direction, weather and sea
conditions (Beaufort) were also recorded during all hours of observation.
For each sighting the radial angle and reticule reading were recorded,
together with the species identification and an estimate of the school
size, as well as a description of any observed behaviours. The presence
of seabirds associated with each sighting, as well as the seabird species
involved, were also noted.
The reticule readings associated
with each sighting were later converted to radial distances. These radial
distances, combined with the radial angles, were then used to calculate
the approximate position of each sighting using standard geometry. Although
the curvature of the earth was not taken into account when calculating
these positions, this effect was likely negligible as radial distances
were usually small (ranging from 0.76 to 4.11 nautical miles (nm), with
mean 1.61nm). This is supported by the fact that radial distances obtained
according to the standard conversion method, which does not take the curvature
of the earth into account, did not differ by more than 0.01nm from radial
distances obtained when accounting for the curvature of the earth.
Besides the shore based
observations, we conducted regular beach surveys for collecting stranded
cetaceans as well as wrecked seabirds. |
 |
Results
and Discussion
A total of 74 days and 561
hours were spent on effort from 7 July to 21 December 2002. Cetaceans were
recorded during 45 days of effort totalling 88 sightings. Seven species
of cetaceans were recorded during our 2002 field work including the humpback
whale (Megaptera novaeangliae), the southern right whale (Eubalaena
australis), the Bryde’s whale (Balaenoptera edeni), the dwarf
minke whale (Balaenoptera acutorostrata), the long-beaked common dolphin
(Delphinus capensis), the bottlenose dolphin (Tursiops truncatus)
and the orca (Orcinus orca). Among small cetaceans the long-beaked
common dolphin was the species most commonly sighted, with a total of
28 (32% of all sightings) groups sighted, followed by the bottlenose dolphin
(n=1, 1%) and the orca (n=1, 1%). Among the large cetaceans we recorded
a total of 22 (25%) groups of humpback whale, 21 (24%) groups of Bryde’s
whale, two groups of dwarf minke whale and one southern right whale. Twelve
groups (14% of all sightings) of cetaceans could not be positively identified
to species level. The distance of groups sighted ranged between 0,5 and
8 nautical miles from the lookout point. Photo: Southern Right whale (Eubalaena
australis) |
 |
Sightings
of the humpback whale (Megaptera novaeangliae)
Humpback whale sightings
were made from July to November, with the exception of October. The peak
in occurrence off Arraial do Cabo was observed in July (n=14 sightings;
63.6%) and August (n=6; 27.3%). Group composition of humpback whales migrating
off Arraial do Cabo in 2002 was comprised of: one adult whale (n=8;
36.4%), 2 adults (n=4; 18.2%), 3 adults (n=1; 4.5%), mother and calf (n=2;
9.1%), mother, calf and escort (n=4; 18,2%), mother, calf and 3 escorts
(n=2; 9,1%) and yearling (n=1; 4,5%).
The records of humpback
whales accompanied by a calf off Arraial do Cabo possibly indicate that
calves are born on their journey to the breeding and calving grounds off
North-eastern Brazil.
Mother and calves while
migrating along the Brazilian coast would have preference for shallow waters
in order to protect their young from potential predators. This hypotheses
should be further investigated by continuos monitoring of whales migrating
off the South-eastern coast of Brazil.
The presence of groups of
mother and calves accompanied by escorts also give evidence of reproductive
behaviour in waters of Arraial do Cabo. |
 |
Sightings
of Bryde’s whale (Balaenoptera edeni)
Bryde´s whales were
observed off Arraial do Cabo during spring and early summer (October
to December). Group composition varied between one to two whales,
including one adult (n=10; 47%), two adults (n=3; 14%), mother and
calf (n=6; 29%) and one juvenile (n=2; 10%).
It was observed that Bryde’s
whales and long-beaked common dolphins usually associate with other marine
vertebrates during feeding events.
Species recorded in each
feeding event included: fish (“bonito”, Euthynnus alleteratus; and
sardines, Sardinella brasiliensis) and seabirds (terns, Sterna spp;
brown boobies, Sula leucogaster; frigate birds,
Fregata magnificens;
and kelp gulls,
Larus dominicanus).
The presence of mother and
calves in nearshore waters off Arraial do Cabo represent new information
on the biology of this poorly known species. Reproductive data on Bryde’s
whale along the Brazilian coast is absent, even from stranded specimens. |
|
Sightings
of the long-beaked common dolphin (Delphinus capensis)
Sightings of long-beaked
common dolphins were made during the whole period of field work. Group
size varied between 1 to ca. 150 individuals. The frequency of occurrence
of groups during the study period was: 1-20 individuals (n=6; 23%), 21-40
(n=9; 34%), 41-60 (n=6; 23%), 61-80 (n=3; 12%) and 81-150 (n=2; 8%). Most
of the observed groups included at least one calf (n=16; 57%).
This data corroborates previous
studies conducted with small cetaceans in the area which have indicated
the year-round presence of long-beaked common dolphins in the waters off
Arraial do Cabo (Hassel, 2003). |
 |
Strandings
A total of 12 strandings
were recorded from July to December 2002 along the eastern coast of Rio
de Janeiro, including nine specimens of the marine tucuxi (Sotalia fluviatilis),
two humpback whales and one Atlantic spotted dolphin.
At least 6 of the Sotalia
specimens and one humpback whale collected had evidence of entanglement
in gill nets.
These entanglements and
subsequent strandings may have resulted from the intense fishery activity
observed on the northern coast of Rio de Janeiro.
Photo: Sperm whale (Physeter
macrocephalus)
|
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Other
marine mammals observed
We reported a southern elephant
seal (Mirounga leonina) on 29 July 2002 at Prainha, Arraial do Cabo.
It was an immature male 3.4m in length, 1.02m wide and weighing approximately
800kg.
The seal was resighted several
times during a five month period on various beaches of Arraial do Cabo
and Saquarema.
A young subantarctic fur
seal (Arctocephalus tropicalis) was observed on 11 September 2002
at Ilha do Farol, Arraial do Cabo.
It was a male, TL 0.95m,
weighing approximately 15kg. |
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Potential
threats to whales and dolphins off Southeastern Brazil
One large whale, possibly
a humpback whale, was reported to have entangled in a gill net set off
Praia Grande, Arraial do Cabo in July 2002.
The humpback whale calf
stranded at Praia do Foguete, Cabo Frio on
3 October 2002 had evidence
of entanglement in gillnets.
The presence of more than
30 oils rigs operating in Campos Basin results in a heavy maritime traffic,
with an increasing number of ships travelling in close proximity to the
coast of Arraial do Cabo, an area with high traffic of touristic and fishery
ships. Additionally, noise production and propagation can potentially disturb
whales while resting or migrating in the area. |
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