Whale surfacing behaviour


Whale surfacing behaviour

Whales exhibit various types of behaviour when they surface. This article describes the different behaviours commonly observed at sea and the possible reasons for the behaviour.

Breaching, lunging and porpoising

A breach or a lunge is a leap out of the water. The distinction between the two is fairly arbitrary: cetacean researcher Hal Whitehead chooses to define a breach as any leap in which at least 40% of the animal's body clears the water, and a lunge as a leap with less than 40% clearance.Fact|date=January 2008 More qualitatively, a breach is a genuine jump with an intent to clear the water as much as possible, whereas a lunge is the result of a fast upward sloping swim, perhaps as a result of feeding, that has caused the whale to clear the surface of the water unintentionally.

Some whales, such as Sperm Whales, perform a breach by travelling vertically upwards from depth, and heading straight out of the water. Others, such as the Humpback Whale, travel close to the surface and parallel to it, and then jerk upwards at full speed to perform a breach. In a typical breach, as performed by a Humpback or Right Whale, the whale clears the water at an angle of about 30° to the horizontal. Around 90% of the body clears the water before the whale turns to land on its back or side. "Belly flops" also occur but are less common. In order to achieve 90% clearance, a Humpback needs to leave the water at a speed of eight metres per second or 29 km/h. For a 36 tonne animal this results in a momentum of 288 thousand N·s. This is close to the whale's maximum speed. It is supposed that other species are also at their limit of power while breaching.

Breaches are often carried out in sessions. The longest sustained series of breaches ever recorded was by a Humpback Whale in the waters around the West Indies—130 separate leaps were recorded in less than 90 minutes. As a whale repeatedly breaches, it typically becomes steadily more tired, and less of the body clears the water.

The Right Whales, Humpback and Sperms are the most prodigious jumpers. However the other baleen whales such as the Fin, Blue, Minke and Sei also breach, but not on such a regular basis. Marine dolphins, including the Orca, are all very common breachers and are in fact capable of lifting themselves completely out of the water very easily.

Many possible reasons have been suggested for breaching behaviour. First, it has been observed that whales are more likely to breach when they are in groups, suggesting that it is done for social reasons, such as an assertion of dominance over another, courting a mate or warning of a danger. Scientists have called this theory a sign of "honest signalling". The immense cloud of bubbles and underwater disturbance caused by a breach cannot be faked. Thus if neighbours detect these bubbles then they know a breach has taken place and, because a single breach costs a whale about 0.075% of its total daily energy intake, [Citation |title=Sperm Whales: Social Evolution in the Ocean |first=Hal |last=Whitehead |page=181 |isbn=0226895173 |url=http://books.google.com/books?id=TKXdCli7nI0C&pg=PA181&lpg=PA181&ots=nOVv644vg2&sig=siDp6CsW78s2aaqhUoPw-Y6qc44] the breach is not to be taken lightly.

It is also possible that the loud "smack" upon re-entering the surface is useful for stunning or scaring fish. Certainly this is believed to be the reason for lobtailing. Others have suggested that a breach allows the whale to breathe in air that is not close to the surface of the water, and so may aid breathing in rough seas. Another widely accepted possible reason is to remove parasites from the skin.

Breaching has also been observed in the following sharks and rays: the great white shark, thresher shark, shortfin mako, longfin mako, spinner shark, blacktip reef shark, salmon shark, porbeagle shark, copper shark and basking shark as well as the manta ray.

pyhopping

Spyhopping is the act of coming out of the water vertically, and momentarily staying out of the water in a manner akin to a human treading water. A powerful individual can spyhop as much as half of its body out of the water. The reasons for spyhopping are likely to be similar to those of breaching. Further spyhops may well be used so that the whale can examine its surroundings above the surface—for instance to look at prey species in the case of Orcas. For this a spyhop may be more useful than a breach, because the view is held steady for a longer period of time. The great white shark and blacktip reef shark have also been known to spyhop.

Lobtailing and slapping

Lobtailing is the act of a whale or dolphin lifting their fluke out of thewater and then bringing it down onto the surface of the water hard and fast in order to make a loud slap. Similarly, species with large flippers may also slap them against the water.

Like breaching, lobtailing is common amongst active cetacean species such as Sperm, Humpback, Right and Gray Whales. It is less common, but still occasionally occurs, amongst the other large whales. Porpoises and river dolphins rarely lobtail, but it is a very common phenomenon amongst oceanic dolphins. It seems that lobtailing is more common within species that have a complex social order than those where animals are more likely to be solitary.

Large whales tend to lobtail by positioning themselves vertically downwards into the water and then slapping the surface by bending the tail stock. Dolphins, however, tend to remain horizontal and make the slap via a jerky whole body movement. All species are likely to slap several times in a single session. The sound of a lobtail can be heard underwater several hundred metres from the site of a slap. This has led to speculation amongst scientists that lobtailing is, like breaching, a form of non-vocal communication. However, studies of Bowhead Whales have shown that the noise of a lobtail travels much less well than that of a vocal call or a breach. Thus the lobtail is probably important visually as well as acoustically, and may be a sign of aggression.

harvtxt|Weinrich|Schilling|Belt|1992 suggest that lobtailing in Humpback Whales is a means of foraging. The theory is that the loud noise causes fish to become frightened, thus tightening their school together, making it easier for the Humpback to feed on them.

Logging

Logging is a behaviour that whales are presumed to exhibit when at rest. [Citation |url=http://science.howstuffworks.com/whale1.htm |title=Howstuffworks |chapter=How Whales Work |accessdate=2006-11-27] It is defined as lying without forward movement at the surface of the water. The dorsal fin or parts of the back are exposed. [Citation |url=http://www.enchantedlearning.com/subjects/whales/ |title=ZOOM WHALES - Enchanted Learning Software |accessdate=2006-11-27] Logging is common, particularly in Right Whales. It can make detecting the whale difficult for humans, especially from a boat. [Citation |url=http://www.coastalstudies.org/what-we-do/right-whales/previous-field-notes2006.htm |title=previous-field-notes2006 |accessdate=2006-11-27]

ee also

* Beached whale

References

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