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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 breath. 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. 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 ) 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.

Porpoising
Porpoising, also known as running, refers to the 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 ms-1 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 ms-1. 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 'crossover' 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 a lot of variation seen in the behaviour cannot be explained by this cause alone; it has likely evolved to provide other functions. For example the extraordinary rotation during porpoising by the spinner dolphin leads to lots of 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 small sharks such as 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-riding
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-1 or when when they are outside of the peak wave energy zone. However, at higher speeds dolphins and porpoises will seek out the pressure wave and it's 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-1 slower in bottlenose dolphin Wave-riding behaviour can be performed by dolphins from minutes up to several hours, and therefore is clearly a useful energy-saving mechanism for swimming at higher speeds.

Wave-riding is most common in small Odontocetes. It has also been observed and filmed 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 behavioural 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 behaviour 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. It has therefore been suggested that position of individuals reflect the dominance hierarchy of the pod and therefore could be used to ascertain dominance, such as a dominant male orca remaining nearest the water's surface a the bow of the boat.

Pectoral slapping
Pectoral slapping, informally known as pec-slapping, is when a cetacean turns on their side, exposes one or both pectoral fins into the air and then slaps it against the surface of the water. It is a form of non-vocal communication commonly observed in a variety of whale and dolphin species as well as seals. The motion is slow and controlled, and the behaviour can occur repeatedly by one individual over a few minutes. Arguably the most spectacular pec-slapping is in the humpback whale, whose pectoral fin is the largest appendage of any mammal and are known for their extremely acrobatic behaviour. Pec-slapping varies between groups of different social structure, such as not occurring in lone males but being common in mother calf pairs and also when they are accompanied by an escort. The reasons for pec-slapping therefore can vary depending on age and sex of individuals humpback whales. During the breeding season adult males pec-slap before they disassociate with a group of males that are vying for a female, whereas adult females pec-slap to attract potential mates and indicate that she is sexually receptive. Its function between mother calf pairs is less well known but is likely to be a form of play and communication that is taught to the calf by the mother for use when it is sexually mature. Pectoral slapping has also been observed in the right whale however due to the smaller size the sound produced will be quieter and therefore used for communication over smaller distances unlike the humpback. Exposure of the pectoral fin and consequent slapping has also been infrequently observed in blue whales, where it is most often a by-product of lunge feeding followed by rolling on to its side.

Logging
Logging is a behaviour that whales exhibit when at rest and appear like "logs" at the surface. It is defined as lying without forward movement at the surface of the water. The dorsal fin or parts of the back are exposed. Whales often rest for periods of time under the surface in order to sleep in mainly horizontal positions, although sperm whales also rest vertically. However as they consciously need to breath at the surface they can only rest one half of their brain at a time, known as unihemispheric slow-wave sleep. This sleep pattern has been identified in all 5 cetacean species that have been tested for it thus far. Cetaceans intermittently come to the surface in order to breathe during these sleep periods and exhibit logging behaviour. Logging can occur interchangeably with surface resting behaviour when cetaceans are travelling slowly, which is particularly common in mother calf pairs as the young tire quickly during swimming. Logging is common, particularly in right whales, sperm whales, pilot whales and humpback whales. Another behaviour that may be mistaken for logging is milling, where a group of cetaceans at the surface have little or no directional movement but instead socialise with each other. This behaviour is particularly common in large groups of pilot whales.

Human interaction
The whale watching industry is popular past time on every continent, with an estimated 13 million people participating in 2008. This, when combined with the sustained increase in boat vessel traffic, has likely affected the surface activity of cetaceans. When boats and other whale watching vessels approach cetaceans most will either avoid or seek interactions. The occasions where no effect is seen is predominantly when the cetaceans are travelling or feeding, but not when they are showing surface activity. In the case of avoidance, the animals may dive rather than staying submerged near the surface or move horizontally away from the vessels. For example, when sperm whales are approached by boats they surface less, shorten the intervals between breathes and don’t show their fluke before diving as often. Cetaceans may also reduce their acrobatic surfacing behaviours, such as when humpback whale groups without calves are approached by vessels within 300 m. Avoidance behaviour is typical of whales, however interactions are more common in whale groups that contain calves and also in the smaller Odontocetes. For example, studies on killer whales in North America have shown that the focal animals increased in tail-slapping behaviour when approached by boats within 100 m, and that 70% of surface active behaviours (SABs) in these orca were seen when a boat was within 225 m. Similarly, dusky dolphins also jump, change direction and form tighter groups more when boats are present, particularly when they do not adhere to the regulations about approach. As an increase in SABs is beneficial to the whale watching tours’ participants the tours may be encouraged to approach cetaceans closer than recommended by the guidelines. There is a lack of understanding about the long-term effects of whale-watching on the behaviour of cetaceans, but it is theorised that it may cause avoidance of popular sites or a decrease in the energy budget for individuals involved.

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