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Pygmy Killer Whale.
Photo: Chris Johnson

June 13, 2003
Pygmy Killer Whales and Sperm Whales
  Real Audio Report
  28k


Log Transcript

This is Genevieve Johnson speaking to you from the Odyssey in Sri Lanka.

One of the most exciting and rewarding aspects of a long-term, oceanic expedition is that the crew is never quite sure of what events each day will bring. We have learned to always expect the unexpected.

Yesterday the crew was among a group of 15 sperm whales. Most of them were small, possibly a group of young males known as a 'bachelor' group. The group engaged in a regular feeding pattern, with most whales remaining at depth for approximately 45 minutes before surfacing to breathe. When they did surface, they formed small clusters of 3-4 animals, travelling slowly together in parallel formation before diving again after about 10 minutes.

Later in the morning, we saw several groups of dolphins, including a large group of more than 200 pantropical spotted dolphins, a few bottlenose dolphins and a small group of rarely seen pygmy killer whales.

Pygmy killer whales are rarely encountered in the wild, although they are believed to have a wide tropical distribution. They are primarily dark gray to black in color with a rounded head, white lips and are the approximate size of the average dolphin, although they are more likely to be confused with the melon-headed whale. When kept in captivity, this species has gained a reputation for being aggressive toward humans and other cetaceans, while evidence suggests that they prey on other dolphins in the wild.

For almost three hours, we observed the pygmy killer whales take a particular interest in the sperm whales. When all the sperm whales were diving, the pygmy killers appeared to take a passing interest in Odyssey, swimming wide circles around us until the sperm whales resurfaced, at which point they suddenly dove, reappearing near the sperm whales. They followed in the wake of the sperm whales, which seemed to stop travelling to log at the surface whenever the pygmy killer whales approached them. The small black whales circled the much larger sperm whales, swimming back and forth in front of them until the sperm whales finally dove. From our perspective on the Odyssey, it was impossible to know whether the pygmy killer whales were harassing the sperm whales, although at times the sperm whales broke their habitual parallel formation with three of four animals all facing different directions.

During the Voyage of the Odyssey, we have observed other species of blackfish, particularly pilot whales, harassing and apparently severely stressing sperm whales. 'Blackfish' is the common name given by fisherman to small toothed whales that are black in coloration. They are generally considered more closely related to dolphins than other whale species and usually include the orca, pilot whale, false killer whale, Risso's dolphin and the smaller and less common melon-headed whale and pygmy killer whale. There are several well-documented cases of orcas harassing and attacking sperm whales and observations of apparent predation or harassment by pilot whales and false killer whales. It is likely that most sperm whales at some stage in their lives are attacked, or at least harassed to some degree by one or more of these species. We often observe white rake marks and scars most likely delivered by the teeth of these animals on various parts of the body, particularly the tail flukes of sperm whales.

It is unclear whether sperm whales are attacked in some instances because they are perceived as competition for food, or because they themselves are viewed as a potential source of food. While the latter, is unlikely to be the reason for pygmy killer whales to attack sperm whales, there are several observations showing that some groups of orcas, so-called transients, have specialized in predation on other marine mammals, including sperm whales and even the enormous blue whale. During such attacks, the orcas will often chase and harass the targeted whales to test them for a sign of weakness, such as illness, injury, young or old age. Top order terrestrial predators such as lions use similar tactics. A pride of females will chase a herd of wildebeest or zebra on the African savannah in order to identify the weakest member.

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The Pygmy killer whales take a particular interest in the group of sperm whales.
Photo: Chris Johnson

It would be fair to assume that animals as large as sperm whales would have little trouble defending themselves. Indeed, accounts of how whales protect themselves have come from many years of experience as their primary predator: Man. Whaling literature is brimming with accounts of whaleboats smashed and sunk by blows from the tail flukes and enraged animals returning to defend an injured calf.

Interestingly, in the instances when attacks on sperm whales by other cetaceans have been observed, they rarely appear to actively defend themselves. A curious lack of response in light of the fact that these animals are the largest predators in the oceans, and are more than well equipped to do so. Instead when threatened by other cetaceans, sperm whales form a protective cluster where all heads are in the center and tail flukes are facing outwards. From above, their bodies look like the petals on a flower; thus, this formation is called the 'marguerite'.

Their superior size and coordinated methods of communal defence appear to keep healthy adults safe most of the time. Yet, one cannot help wondering why an animal with unparalleled abilities as a diver, does not simply do so in order to escape or at the very least, thrash its tail at its tormentors? Sometimes the group may stay in a marguerite formation to protect their young, which are unable to dive for extended periods and are placed in the center of the group. However, this behavior has been witnessed when all animals involved were adults. In 1999 off the coast of California, a group of nine adult females formed a marguerite and attempted to hold the formation for several hours, despite repeated attacks from orca's. When one animal was dragged from the relative safety of the group, one and sometimes two sperm whales left the group in an apparent attempt to assist their stricken companion, even though doing so meant exposing themselves to the full brunt of the attack. In this particular case, at least one sperm whale was killed and several others were severely, perhaps even mortally wounded. (Pitmann and Chivers 1999)

It is impossible to determine the reason for many observed behaviors in cetacean species. We can only hope that by observing and recording rarely seen interactions in the wild, such as the one the crew witnessed between pygmy killer whales and sperm whales, that it will assist us in gaining a greater understanding of the mysterious lives of cetacean species and how they interact .

Links:

Reference:

  • Cetacean Societies - Field Studies of Dolphins and Whales.
    Mann, Connor, Tyack and Whitehead.
    University of Chicago Press, 2000.

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