Whale killers – Killer whales (Orcinus orca)

 

It has been well documented throughout history that orcas are a hunter of all species of great whales. Scarring from orcas’ teeth on 1/3 of Humpback whales found off Newfoundland and Labrador indicate they do not always succeed in killing their prey. However, killing their prey is not always a necessity to acquire sustenance; chunks and strips have been witnessed being torn off a humpback in an attack by several orcas. Even the largest mammal, the blue whale, has not been immune from predation from transients (killer whale type specific to NE Pacific). An extended attack from a pod of orcas was observed that resulted in the dorsal fin and flukes being completely chewed off making swimming and escape impossible while a six feet square cavity was excavated in the side of the body from the attack.

Defence mechanisms and behaviour modifications have developed among the great whale in response to predation; harassed grey whales have been seen to rotate along their longitudinal axis and move toward the shore. The reason suggested for this is that in shallow water they can use the tail flukes to lash out and the rolling motions prevent orcas from grabbing on to their pectoral fin. Sperm whales have been seen to form a protective ‘rosette’ with their tails radiating outwards. This does not appear to act as a deterrent to attacking orcas (or afford the sperm whales greater protection) but it does seem to even out the odds of being attacked with no one individual being singled out by the attacking pod. Orcas seem to undertake an ‘attack and retreat’ strategy when preying on large whales;  the superior size of the great whale could wound the orcas in a prolonged attacked. It has been suggested that the objective of their ‘attack and retreat’ strategy is to exsanguinate and finally kill through minimal contact.

References

Barrett-Lennard, L.G. Matkin, C.O. Durban, J.W. Saulitis, E.L. 2011. Predation on gray whales and prolonged feeding on submerged carcasses by transient killer whales at Unimak Island, Alaska. Marine Ecology Progress Series. Vol. 421

Jefferson, T.A. Stacey, P. Baird, R.W.1991. A review of killer whale interactions with other marine mammals: predation to co-existence. Mammal Review, Vol. 21, No. 4.

Orcas: Killer Beauties. Orca attacj. 2011. Available at: http://orcaskiller beauties.delfinweb.org/orca_attack_en.htm [Accessed 15th October 2014].

Pitman, R.L. Balance, L.T. Mesnick, S.I. Chivers, S.J. 2001. Killer whale predation on sperm whales: Observations and implications. Marine Mammal Science, 17 (3)

Whitehead, H. Glass, C.  1985. Orcas (killer whales) attack Humpback whales. Journal of Mammals 66 (1).

Whitehead, H. Reeves, R.  2005. Killer whales and whaling: the scavenging hypothesis. Biology Letters: 1.

 

 

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