Cetacean surfacing behaviour
Cetacean surfacing behaviour is a grouping of movement types that cetaceans make at the water's surface in addition to breathing. Cetaceans have developed and use surface behaviours for many functions such as display, feeding and communication. All regularly observed members of the infraorder 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, when considering behaviour, Cetacea can be split into whales and dolphins and porpoises 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, 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 defines 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 widely observed 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 clears 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 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. Repeated breaches tire the animal, so 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-verbal 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.
Porpoising
Porpoising, also known as running, is a high speed surface behaviour of small cetaceans where long jumps are alternated with swimming close to the surface. Despite the name, porpoising behaviour is seen in dolphins and porpoises, as well as other marine species such as penguins and pinnipeds. When marine mammals are travelling at speed they are forced to stay close to the surface in order to maintain respiration for the energetic exercise. At leisurely cruising speeds below 4.6 m/s, dolphins swim below the water's surface and only briefly expose their blowholes along with up to one third of their body at any one time. This results in little splashing as they have a very streamlined shape. Porpoising occurs mainly when dolphins and porpoises are swimming at speeds greater than 4.6 m/s. Here, jump length is roughly equal to distance traveled when the cetaceans are submerged. This exposes the blowhole for longer which is needed to get enough oxygen to maintain metabolism and therefore high speeds over long periods of time. Studies have also shown that leaping is more energetically efficient than swimming above a certain threshold speed. This is due to the reduction in friction when travelling in air compared to water which saves more energy than is needed to produce the leap. These benefits also outweigh the energy wasted due to the large amount of splashing often seen when groups are porpoising. Porpoising is therefore a result of high speed swimming which cetaceans use for important pursuit and escape activities. For example, dolphins may be seen porpoising away from their main predator, sharks or the direction of incoming boats to avoid collision.Although porpoising is a useful product of rapid swimming, much variation seen in the behaviour cannot be explained by this cause alone; it has likely evolved to provide other functions. For example, the rotation during porpoising by the spinner dolphin leads to much splashing and is more common at slower speeds so cannot be attributed to an energy saving mechanism. It is therefore more likely to be a form of play or communication within or between pods. Another reason might be to remove barnacles or remoras that, when attached, increase drag during swimming. When spinner dolphins impact the water the combination of centrifugal and vertical force upon these ectoparasites can be up to 700 times their own weight and so efficiently remove them. Other theories suggest that cetaceans may porpoise in order to observe distant objects such as food by looking for visual cues, such as birds dive-bombing a bait ball. Research into the additional functions of porpoising has so far been focussed on the more acrobatic species, but it is likely that other cetaceans also use it for these, and perhaps unknown, reasons too.
Wave or bow-riding and following vessels
The term wave-riding is most commonly used to describe the surface activity of cetaceans that approach boats and jump repeatedly in the waves produced by the boats. This includes bow-riding, where cetaceans are in the pressure wave in front of the boat, and wake-riding, where they are off the stern in the wake. Cetaceans swim using fluke propulsion when experiencing wave energy below the threshold needed for riding, such as when boats travel at speeds slower than 3 m/s or when they are outside of the peak wave energy zone. However, at higher speeds dolphins and porpoises will seek out the pressure wave and its maximum energy zone in order to ride the wave by holding their flukes in a fixed plane, with only minor adjustments for repositioning. Wave-riding reduces the energetic cost of swimming to the dolphin, even when compared to slower swimming speeds. For example, heart rate, metabolic rate and transport cost was reduced by up to 70% during wave-riding compared to swimming at speeds 1 m/s slower in bottlenose dolphin. Wave-riding behaviour can be performed by dolphins from minutes up to several hours, and therefore is a useful energy-saving mechanism for swimming at higher speeds.Wave-riding is most common in small Odontocetes. It has also been observed in larger cetaceans such as false killer whales and orca, although most larger Odontocetes do not seek out any form of interaction with boats. Bow-riding is the most common form of interactive behaviour with boats across a variety of smaller Odontocete species, such as dolphins in the genera Stenella and Delphinus. The type of interaction can often depend on the behavioral state of the group as well as species. For example, spotted dolphins are more likely to interact when travelling or milling but less likely when they are socialising or surface feeding. Interactive behavior may also depend on group composition, as both orca and bottlenose dolphins have been recorded to interact mostly when a calf was in the group. This indicates that groups with calves may approach boats in order to teach the young how to interact safely to avoid collision. Another result of cetaceans traveling in pods is an increase in competition for the optimal wave energy and so maximum energy saving position. Position of individuals may reflect the dominance hierarchy of the pod and therefore could be used to ascertain dominance. Several rorquals, such as minke, sei, bryde's, humpback, and gray are also known to display actions in similar manners.