Killer whales preying on a blue whale calf on the Costa Rica Dome: genetics, morphometrics, vocalizations and composition of the group

Citation:
Pitman, R, Fearnbach H, LeDuc R, Gilpatrick JW, Ford JKB, Ballance LT.  2007.  Killer whales preying on a blue whale calf on the Costa Rica Dome: genetics, morphometrics, vocalizations and composition of the group. Journal of Cetacean Research and Management. 9(2):151-158.

Abstract:

Killer whale (Orcinus orca) populationsin high latitude, nearshore areas appearto regularly exhibit prey specialisation among two or more
sympatric ecotypes, but nearly nothing is known about populations that inhabit open ocean areas or tropical latitudes. On 26 September
2003, during a cetacean survey in the eastern tropical Pacific Ocean, a group of an estimated 19 killer whales was encountered feeding on
a calf of a blue whale (Balaenoptera musculus); the location was 10°58’N, 88°40’W, 230km west of Nicaragua. The whales were studied
for 2.5 hours and during thistime skin biopsy samples were collected, acoustic recordings made, aerial and lateral photographstaken and
behavioural observations recorded. The 19 individuals identified included 4 males (3 adults, 1 subadult), 5 cow-calf pairs and 5 other
females/subadult males. Using aerial photogrammetry, body lengths of 17 different animals were measured: the largest male (who carried
the carcassmost ofthe time) was 8.0mlong; and the largestfemale (with a calf) was 6.1m. From10 biopsy samples, two distinct haplotypes
were identified that differed from resident (i.e. fish-eating ecotype) killer whales in the northeastern Pacific by one and two base pairs,
respectively.The single discrete callrecorded was a typical killer whale call but it had a two-part pitch contourthat wasstructurally distinct
from callsrecorded to date in the North Pacific. These observationsreaffirm that calves of even the largest whale species are vulnerable to
predation, although by migrating to calving areas in the tropics, where killer whale densities are lower, baleen whales should be able to
increase their overall reproductive fitness, assuggested by Corkeron and Connor (1999).