Sperm Whale's chronicles

What Can Be Dangerous To a Sperm Whale?

As stranger as it may sound like, sperm whales are not in the top of marine food chain. It means that sperms can be predators and preys. The most serious predator of sperm whales is the Homo sapiens, as known as human, but we have been their predators since 1712, so we are not their “natural” enemies [6]. I’ll talk about the hunt of sperm whales in the next post!

The most important predator of sperm whales are orcas (Orcinus orca), known as killer whales (as seen in the video below), but other species also attack sperm whales: pilot whales (Globicephala spp.) and false killer whales (Pseudorca crassidens) [6], however, there were no fatalities recorded for attacks of these 2 species [6].

But orcas don’t always hunt sperm whales [6]. In the eastern Pacific there is a group of sperm whales that has been observed at least 4 times in the same area of orcas but in only one of these there was a sign of attack by the orcas [6].

Whitehead (2003) summarises some attacks of orcas in Galápagos and in the Eastern North Pacific, where, in the most dramatic of all described attacks, 9 sperm whales were hunted by 35 orcas. The pod of sperm whales ended severely hurt and it is likely that the entire group died as a result of the attack.

Predation is unlikely to be a significant influence on the mortality of adult sperm whales [6]. However, the potential for predation on calves may have been important in sperm whales evolution [6].

But how do sperm whales protect themselves of these attacks?

Scientists observed that sperm whales react to orca’s presence: they stop foraging dives, come to the surface and swim fast towards each other, and cluster actively and tightly [6]. During the observations, sperm whales didn’t tempt flight or deep dives as an escape method [6]. They also believe that these strategies wouldn’t work, because of the greater speed of orcas and the probable ability to detect sperms under water using echolocation [6]. Some “heroic” acts were observed in Californian groups of sperms: some of the whales in the defensive position left the group to rescue a detached member, taking a personal risk [6].

Two main defensive formations were observed in sperm’s pods characterized by the orientation of the sperm whales relative to their attackers: the rosette (Fig. 1) and heads-out (Fig. 2) formations [6]. The defence formation may be adapted to the behaviour of the attacker or it may depend of the characteristic defensive method of a specific pod [6].

Figure 1: Rosette formation adopted by sperm whale’s pod.

Figure 1: Rosette formation adopted by sperm whale’s pod. Source: Whitehead, 2003.

Figure 2: “Heads-out” formation adopted by sperm whale’s pod. Source: Whitehead, 2003.

Figure 2: “Heads-out” formation adopted by sperm whale’s pod. Source: Whitehead, 2003.

This next video is an animation of an underwater take where you can see how the rosette formation works.

After seeing in the previous video how it works, you can see the same rosette formation in nature in this next video.

Summarising: when attacked by orcas, sperm whales gather quickly and closely to the surface and stay in one of two defensive formations: “rosette” or “heads-out”. Defensive behaviour against human whaling consists in long and deep dives.

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