Brennan, Bernard

Rodriguez, Patricia

English

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28 NOTICIAS DE GALAPAGOS No.54
REPORT OF TWO ORCAATTACKS ON CETACEANS
IN GALÁPICOS
By: Bernard Brennan and Patricia Rodriguez
-
The Research Vessel Odyssey studied sperm
whales (Phy s ete r macrocephahzs) and other cetaceans
in the Galápagos Archipelago from February 1993 to
April 1994. During the tenth cruise around the is-
lands, from 17 October to 6 November 1993, orcas
(killer whales, Orcinus orca) were observed attack-
ing Bryde's whales (Balaenoptera edeni) and sperm
whales on two consecutive days.
Orcas are regularly seen in the Galápagos Archi-
pelago (Day, 1994). However, only one orca attack
on another cetacean (sperm whales) in Galápagos
has been reported (Arnbom et al., 198'7 ). Two other
unpublished incidents have been noted by local nat-
uralists: one involving bottlenose dolphins (Tursiops
truncatus) and the other, common dolphins (Delphi-
nus delphis).
THE ATTACKS
At 0830 h on 25 October 1993, a group of at least
five Bryde's whales was observed being pursued by
ten orcas in Banks Bay, north of Fernandina Island
(initial sighting: 0'08. 85, 9 1'32. 8W). The orcas were
spread out in small groups of one to three individuals,
following and flanking the Bryde's whales. Half the
orcas soon disappeared from sight leaving two males,
a mother and calf, and another female. Individuals
were distinguished by size, dorsal fin shape and be-
havior. V/hile being pursued, the Bryde's whales
traveled as a closely knit group, made mostly short
dives and increased their blow rate. One individual
breached twice. On several occasions, the two male
orcas converged from opposite sides of a Bryde's
whale and then the three animals submerged, pre-
venting further observations of any interactions. No
physical contact, open flesh wounds or carcasses were
seen. However, blood was observed at the surface
and the orcas were seen feeding on pieces of flesh and
intestines. Therefore, we believe that aBryde's whale
may have been killed. No sounds were heard on our
hydrophones otherthan an orcasqueal and some clicks
on two occasions. The interaction between the two
species was observed for two and a half hours until
the Bryde's whales left the area.
The second attack occurred the following day at
1530 h while the Odyssey was following a dispersed
group of 12 sperm whales, 8.5 miles southwest of
Fernandina (0"28.95, 91'45.5W). An orca was ob-
served to porpoise out of the water and bite a sperm
whale behind the dorsal fin. Two lnore orcas were
seen immediately behind the attacked sperm whale
before all the animals submerged. Alarge expanse of
blood subsequently formed at the surface. Several
minutes later a group of five orcas (a large male, a
mother and calf, and two females or immature males)
were sighted. They circled the expanse of blood at
high speed, then left the area. The interactions lasted
less than seven minutes. Meanwhile, the remaining
sperm whales tightened their group at the surface and
made frequent direction changes. They ceased mak-
ing deep or long dives and were mostly silent. This
behavior was observed until nightfall (1835 h) when
it became impossible to follow the whales. As far as
it could be determined, only one sperm whale was
attacked.
The proximity of these two attacks in space and
time, and the similar composition of the two orca
groups, suggested that some of the orcas were in-
volved in both incidents. Howevet, analysis of
photographs of the dorsal fins and white "saddle"
markings of each individual has revealed that the two
groups were distinct.
The Bryde's and sperm whales demonstrated
marked behavioral responses to the presence of or-
cas. Both species formed tighter groups than normal,
made frequent directional changes as a group and
ceased making long dives. These responses and par-
ticularly the breaching of one of the Bryde's whales
November 1994 NOTICIAS DE GALAPAGOS 29
and the prolonged silence of the sperm whales, differ
from anything that has been observed in Galápagos
during the past years'work on board the Odyssey.
ACKNOWLEDGMENTS
The authors would like express their appreciation
to the scientific team aboard RN Odyssey: Captain
Iain Kerr, Daniel Palacios, Erland Lettevall, Christo-
pher Rogers, David Day, and Robert Wallace. Ana
Lucia Benitez, James Prentice and Kirsten Anthon
also helped with data collection. The Servicio Parque
Nacional Galápagos, the Charles Darwin Research
Station and the Ecuadorian Ministry of Defense ap-
proved and supported the scientific work of R/V
The Cuvier's beaked whale (Ziphius cavirostris)
is a poorly known member of the cetaceans found in
Galápagos. During research cruises aboard the R/V
Odyssey in1993 and1994 we only saw this species
about 15 times during 13 months. However, we were
lucky to find a dead individual which prompted the
writing of this note. Our observations on this individ-
ual follow a brief description of Cuvier's beaked
whales paraphrased from Leatherwood et al. s ( 1 9 8 8)
identification guide to whales.
The Cuvier's beaked whale, or goose beaked
whale, belongs to aninteresting anddiverse, butpoorly
known, group of odontocete cetaceans, the family
Ziphlidae. Most of what is known about this group
comes from individuals stranded on shore. Since
Ziphiids tend to be shy and relatively inconspicuous
at the surface, they are infrequently seen at sea.
Cuvier's beaked whales grow to about 7 m, be-
coming sexually mature at about 5.4 m. Length at
birth is 2to3 m. The head is relatively small and the
Odyssey. TAME provided reduced airfare between
Galápagos and continental Ecuador.
LITERATURE CITED
Arnbom, T., V. Papastavrou, L. Weilgart and H.
Whitehead. 1987. Sperm whales react to an at-
tack by killer whales. Journal of Mammalogy.
68(2):450-453.
Day, D. 1994. Ltst of cetaceans seen in Galápagos.
Noticias de Galápagos 53, Aprll1994.
Bernard Brennan and Patricia Rodriguez, Whale
Conservation Institute, 191 Weston Road, Lincoln,
MA 01773, USA.
beak is short and poorly demarcated. The profile of
the head and jaw appears similar to a goose's beak. A
single pair of conical teeth is located under the gum,
at the tip of the lower jaw. These teeth emerge only
in males and visibly protrude from the closed mouth.
The throat has two long, anteriorly convergent creas-
es. The dorsal fin, located well behind the central
dorsal region, tends to vary in size and shape. Unlike
in othercetaceans, the flukes of Cuvier's beakedwhale
are usually not divided by a distinct notch and their
trailing edge is somewhat concave.
Coloration appears to be related to both age and
sex. Calves and juveniles are tan or light brown. As
they age, they becomes marred with scratches and
white or cream-colored oval blotches, especially on
the abdomen. In older animals the head becomes
distinctively lighter than the rest of the body. Old
males may appear all white.
Cuvier's beaked whales are probably deep divers
since they prey mostly on squid and deepwater fish.
NOTES ON THE CUVIER'S BEAKED WHALE (ZIPHIUS
cAvrRosrRls), wrrH OBSERVATIONS OF A DEAD SPBCIMEN
By: Daniel M. Palacios, Patricia Rodriguez,
Bernard Brennan and Kim Marshall


Report of two Orca attacks on cetaceans in Galápagos

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Report of two Orca attacks on cetaceans in Galápagos

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