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Cetacean surfacing behaviour is a group of unique behaviours demonstrated by the Cetacea order when they come to the water's surface to breathe. Time intervals between surfacing can vary depending on the species, surfacing style or the purpose of the dive, and some species have been known to dive for up to 85 minutes at a time when hunting.〔(), "The Deepest Divers," Oceanus Magazine, Woods Hole Oceanographic Institute.〕 In addition to respiration, cetaceans have developed and use surface behaviours for many other functions such as display, feeding and communication. All regularly observed members of the order Cetacea, including whales, dolphins and porpoises, show a range of surfacing behaviours. Cetacea is usually split into two suborders, Odontoceti and Mysticeti, based on the presence of teeth or baleen plates in adults respectively. However, for the purpose of this article Cetacea will be split into whales (large (> 10 m) sized cetaceans such as sperm and most baleen whales) and dolphins and porpoises (all medium and small sized (< 10 m) Odontocetes including orca〔(), FAO Marine Mammals of the World, Suborder Odontoceti.〕) as many behaviours are correlated with size. Although some behaviours such as spyhopping, logging and lobtailing occur in both groups, others such as bow riding or peduncle throws are exclusive to one or the other. It is these energetic behaviours that humans observe most frequently and are generally most fascinated with, which has resulted in a large amount of scientific literature on the subject and a popular tourism industry. == Travelling surface behaviour == === Breaching and lunging === A breach or a lunge is a leap out of the water also known as cresting. 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. Qualitatively, a breach is a genuine jump with an intent to clear the water, whereas a lunge is the result of a fast upward-sloping swim that has caused the whale to clear the surface of the water unintentionally. This latter "lunging" behaviour is often a result of feeding in rorquals. The right, humpback and sperm whales are the most well-known jumpers. However other baleen whales such as fin, blue, minke, gray and sei whales also breach. Oceanic dolphins, including the orca, are very common breachers and are in fact capable of lifting themselves completely out of the water very easily, although there is little distinction between this and porpoising. Some non-cetacean marine creatures also exhibit breaching behavior, such as several shark species and rays of the genera ''Manta'' and ''Mobula''. Two techniques are used by cetaceans in order to breach. The first method, most common in sperm and humpback whales, is conducted by swimming vertically upwards from depth, and heading straight out of the water. The other more common method is to travel close to the surface and parallel to it, and then jerk upwards at full speed with as few as 3 tail strokes to perform a breach.〔 In all breaches the cetacean clear the water with the majority of its body at an acute angle, such as an average of 30° to the horizontal as recorded in sperm whales. The whale then turns to land on its back or side, and less frequently may not turn but "belly flop" instead. In order to achieve 90% clearance, a humpback needs to leave the water at a speed of eight metres per second or . For a animal, this results in a momentum of 288 thousand newton seconds. Despite its obvious energetic cost, breaching is often carried out in series. The longest recorded sustained series was by a humpback near the West Indies totaling 130 leaps in less than 90 minutes.〔(【引用サイトリンク】title=Whale Behaviour )〕 Repeated breaches tire the animal, so that less of the body clears the water each time.〔>〕 Ultimately, the reasons for breaching are unknown; however, there is evidence to support a range of hypotheses. Whales are more likely to breach when they are in groups, suggesting that it is a non-acoustic signal to other group members during social behaviour. Scientists have called this theory "honest signalling". The immense cloud of bubbles and underwater disturbance following a breach cannot be faked; neighbours then know a breach has taken place. A single breach costs a whale only about 0.075% of its total daily energy intake, but a long series of breaches may add up to a significant energy expenditure.〔 A breach is therefore a sign that the animal is physically fit enough to afford energy for this acrobatic display, hence it could be used for ascertaining dominance, courting or warning of danger.〔 It is also possible that the loud "smack" upon re-entering is useful for stunning or scaring prey, similar to lobtailing. As breaching is often seen in rough seas it is possible that a breach allows the whale to breathe in air that is not close to the surface and full of spray, or that they use breaching to communicate when the noise of the ocean would mask acoustic signals. Another widely accepted possible reason is to dislodge parasites from the skin.〔 The behaviour may also be more simply a form of play.〔 Breaching is therefore undoubtedly a very important part of socialising in cetaceans, and is learnt by all cetaceans at an early age from conspecifics. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cetacean surfacing behaviour」の詳細全文を読む スポンサード リンク
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