Dolphin Frequently Asked Questions

How do dolphins sleep?
Dolphins have to be conscious to breath (Williams et al, 1990). This means that they cannot go into a full deep sleep, because then they would suffocate. Dolphins have "solved" that by letting one half of their brain sleep at a time. This has been determined by doing EEG studies on dolphins. Dolphins sleep about 8 hours day in this fashion. REM (Rapid Eye Movement) sleep, usually associated with dreaming has been recorded only very rarely. Some scientists claim dolphins do not have REM sleep at all.

A dolphin's behavior when sleeping/resting depends on the circumstances and possibly on individual preferences. They can either: - swim slowly and surface every now and then for a breath - rest at the surface with their blowhole exposed - rest on the bottom (in shallow water) and rise to the surface every now and then to breath.

sources: S.H Ridgway (1990) The Central Nervous System of the Bottlenose Dolphin, in S. Leatherwood and R.R. Reeves: The Bottlenose Dolphin, pp. 69-97, Academic Press

Th.D. Williams, A.L. Williams and M. Stoskopf (1990) Marine Mammal Anesthesia. In: L.A. Dierauf (ed.): Handbook of Marine Mammal Medicine: Health, Disease and Rehabilitation, pp. 175-191 CRC Press, Boca Raton

How intelligent are dolphins?
The short answer to this is that we do not know. There is no reliable method to measure intelligence in humans across cultures, so it is not surprising that comparing humans, dolphins, apes, dogs, etc. is impossible. There are some indications of their potential: they are fast learners and can generalize (which is also true of pigs, BTW). Also they can learn to understand complicated language-like commands (which is also true of the great apes).

How do dolphins communicate; do they have their own language?
Dolphins communicate mainly by means of sounds. These sounds include whistles, but also so-called pulsed sounds, which are often described as squawks, barks, rasps, etc. But they also use breaching (jumping and falling back into the water with a loud splash) and pectoral fin (or flipper) and tail (or fluke) slaps (hitting the flipper or fluke on the water surface). Body posturing and jaw popping also have a role in communication. This list is not exhaustive.

As for language, we do not know if they have one. Several studies have demonstrated that dolphins can understand a structured language like ours. This same has been demonstrated for a number of other animals species as well (gorilla, bonobo, California sea lion, parrot). Some studies also indicate that dolphin vocalizations are complex enough to support some form of language. However, to date it has not been demonstrated yet that they indeed use a language for communication among themselves.

How does dolphin sonar work?
Dolphins (and other toothed whales) can produce high pitched clicks. When these clicks hit an object, some of the sound will echo back to the "sender". By listening to the echo and interpreting the time it took before the echo came back, the dolphin estimate the distance of the object. (That's why sonar is also called echolocation: with information from the echoes, a dolphin can locate an object). Depending on the material the object is made of, part of the sound may penetrate into the object and reflect off internal structure. If the object is a fish, some sound will reflect off the skin on the dolphin's side, some of the bones, the internal organs and the skin on the other side. So one click can result in a number of (weaker) echoes. This will give the dolphin some information about the structure and size of the fish. By moving its head (thereby aiming the clicks at other parts of the fish) the dolphin can get more information on other parts of the fish.

It is like a medical ultrasound probe, but the results are far less clear. A medical probe moves back and forth very rapidly, much faster than a dolphin can move its head. Also the frequency of the sounds of the medical probe is much higher than a dolphin's sonar. Therefore the level of detail the echoes can provide is much higher in the medical probe.

For technical information on dolphin sonar, check out the following book: W.W.L.Au (1993) The sonar of dolphins. (Springer-Verlag New York).

Can dolphins combine information from their sonar with their vision?
The short answer is: yes, they can. Just like people can visualize an object by just touching it, dolphins can get an idea of what an object looks like by scanning it with their sonar. They can also identify objects with their sonar that they have only been able to see. If they form a visual picture from the sonar information (visualization) or form an acoustical picture from visual information is still unresolved. This capability is called cross-modal transfer and it has been demonstrated in only a few animal species so far: the bottlenose dolphin and the California sea lion. See the following references for more details on this subject.

R.J. Schusterman, D. Kastak and C. Reichmuth (1995) Equivalence class formation and cross-modal transfer: testing marine mammals.

In: R.A. Kastelein, J.A. Thomas and P.E. Nachtigall (eds): Sensory systems of Aquatic Mammals, pp. 579-584 De Spil Publishers, Woerden, the Netherlands ISBN 90-72743-05-9

A.A. Pack and L.M. Herman (1995) Sensory integration in the bottlenosed dolphin: Immediate recognition of complex shapes across the senses of echolocation and vision

J. Acoustical Society of America 98(2) Part 1: 722-733

What and how much do dolphins eat?
Bottlenose dolphins eat several kinds of fish (including mullet, mackerel, herring, cod) and squid. The composition of the diet depends very much on what is available in the area they live in and also on the season.

The amount of fish they eat depends on the fish species they are feeding on: mackerel and herring have a very high fat content and consequently have a high caloric value, whereas squid has a very low caloric value, so to get the same energy intake (calories) they will need to eat much more if they feed on squid than if they feed on mackerel or herring.

On average an adult dolphin will eat 4-9% of its body weight in fish, so a 250 kg (550 lb) dolphin will eat 10-22.5 kg (22-50 lb) fish per day.

How old can they get?
The maximum age for bottlenose dolphins is between 40 and 50 years. The average age a dolphin can get (the life expectancy) can be calculated from the Annual Survival Rate (the percentage of animals alive at a certain point, that is still alive one year later). For the dolphin population in Sarasota Bay, the ASR has been measured to be about 0.961. This yields a life expectancy of about 25 years. For the population in the Indian/Banana River area, the ASR is between 0.908 and 0.931.

This yields a life expectance between 10.3 and 14 years. So the actual life expectancy differs per region.

sources: R.S. Wells and M.D. Scott (1990) Estimating bottlenose dolphin population parameters from individual identification and capture-release techniques. Report International Whaling Commission (Special Issue 12): 407-415

S.L.Hersch, D.K.Odell, E.D.Asper (1990) Bottlenose dolphin mortality patterns in the Indian/Banana River System of Florida, in S. Leatherwood and R.R. Reeves: The Bottlenose Dolphin, pp. 155-164, Academic Press

Do dolphins live shorter in captivity?
No. A recent study, comparing the survival of dolphins in captivity from 1940 through 1992 showed no significant difference in ASR between the "captive population" and the Sarasota Bay population. The ASR for the captive population was 0.944 (life expectancy: 17.4 years). Also in captivity dolphins have reached ages over 40 years.

source: R.J.Small and D.P.DeMaster (1995) Survival of five species of captive marine mammals. Marine Mammal Science 11(2):209-226.

How did dolphins evolve?
The earliest recognizable cetaceans lived about 50 million years ago. These evolved from the Mesonychids: large land mammals, some of which were carnivorous, some herbivorous. The earliest cetaceans were members of the now extinct family Archaeoceti (the best known of which are Zeuglodon and Basilosaurus). 38-25 million years ago the Archaeoceti disappeared and were replaced by the early Odontocetes (toothed whales) and Mysticetes (baleen whales). The earliest dolphins appeared in the late Miocene period, some 11 million years ago.

The land animals that are closest to whales and dolphins are the Ungulates (hoofed animals). This was determined among others by comparing the structure of body proteins.

source: P.G.H.Evans (1987) The Natural History of Whales and Dolphins. Christoper Helm Publishers, London.

How can you interact with wild dolphins?
When swimming, boating or snorkeling in certain areas you can encounter wild dolphins. Keep in mind that in the US it is illegal to directly approach dolphins. If dolphins come towards you and choose to interact, that is allowed. In several areas there are boat operators that can take you to areas where there is a good chance to encounter dolphins (Florida, Bahamas). A note of warning: there have been operators that have tried to lure dolphins by feeding them. This is illegal in the US and is highly undesirable, because it changes the dolphins' behavior. Currently there are operators offering bird-feeding tours. These bird feedings take place in areas frequented by dolphins and are an attempt to circumvent the dolphin feeding ban. Do not use these operators.

Why do whales and dolphins beach themselves?
If a single whale or dolphin strands, it usually is a very sick (and exhausted) animal. Such an animal often has some infections (pneumonia is almost always one of them) and a lot of parasites (worms in the nasal passages are very common). Sometimes these animals can be rehabilitated, but often they are so sick they won't make it.

Some species of whales and dolphins occasionally strand in groups. A stranding of 2 or more animals is usually called a mass stranding. There are a number of theories that try to explain the occurrence of mass strandings. No theory can adequately explain all of them. In some cases it will be a combination of causes. The most common explanations are:

- deep water animals (the species that most often are the victim of mass strandings) can not "see" a sloping sandy beach properly with its sonar. They detect the beach only when they are almost stranded already and they will panic and run aground.

source: W.H. Dudok van Heel (1962): Sound and Cetacea. Neth. J. Sea Res. 1: 407-507

- whales and dolphins may be navigating by the earth's magnetic field. When the magnetic field is disturbed (this occurs at certain locations) the animals get lost and may run into a beach.

source: M. Klinowska (1985): Cetacean live stranding sites relate to geomagnetic topography. Aquatic Mammals 11(1): 27-32

- in some highly social species, the group leader may be sick and wash ashore. The other members try to stay close and may strand with the group leader.

source: F.D. Robson (?) The way of the whale: why they strand. (unpublished manuscript)

- when under severe stress or in panic, the animals may fall back to the behavior of their early ancestors and run to shore to find safety.

source: F.G. Wood (1979)

The cetacean stranding phenomena: a hypothesis. In: J.B. Geraci and D.J. St. Aubin: Biology of marine mammals: Insights through strandings. Marine Mammal Commission report no: MMC-77/13: pp. 129-188

How deep can dolphins dive?
The deepest dive ever recorded for a bottlenose dolphin was a 300 meters (990 feet). This was accomplished by Tuffy, a dolphin trained by the US Navy. Most likely dolphins do not dive very deep, though. Many bottlenose dolphins live in fairly shallow water. In the Sarasota Bay area, the dolphins spend a considerable time in waters that are less than 2 meters (7 feet) deep.

Other whale and dolphin species are able to dive to much greater depths even. The pilot whale (Globicephala melaena) can dive to at least 600 meters (2000 feet) and a sperm whale (Physeter macrocephalus) has been found entangled in a cable at more that 900 meters (500 fathoms) depth.

Recent studies on the behavior of belugas (Delphinapterus leucas) has revealed that they regularly dive to depths of 800 meters. The deepest dive recorded of a beluga was to 1250 meters.

sources: F.G. Wood (1993) Marine mammals and man. R.B. Luce, Inc., Washington. E.J. Slijper (1979) Whales, 2nd edition. Cornell University Press, Ithaca, NY. (Revised re-issue of the 1958 publication: Walvissen, D.B. Centen, Amsterdam). R.S. Wells, A.B. Irvine and M.D. Scott (1980) The social ecology of inshore odontocetes. In: L.M. Herman (ed.): Cetacean Behavior. Mechanisms & functions, pp. 263-317. John Wiley & Sons, New York A.R. Martin (1996) Using satellite telemetry to aid the conservation and wise management of beluga (Delphinapterus leucas) populations subject to hunting. Paper presented at the 10th Annual Conference of the European Cetacean Society, March 11-13, 1996, Lisbon, Portugal.

How fast can dolphins swim?
The dolphin's fast cruising speed (a traveling speed they can maintain for quite a while) is about 3-3.5 m/s (6-7 knots, 11 - 12.5 km/hr). They can reach speeds of up to 4.6 m/s (9.3 knots, 16.5 km/hr) while traveling in this fashion. When they move faster, they will start jumping clear of the water (porpoising). They are actually saving energy by jumping. When chased by a speedboat, dolphins have been clocked at speeds of 7.3 m/s (14.6 knots, 26.3 km/hr), which they maintained for about 1500 meters, leaping constantly.

Energetic studies have shown, that the most efficient traveling speed for dolphins is between 1.67 and 2.27 m/s (3.3-4.5 knots, 6.0-8.2 km/hr).

There have been reports of dolphins traveling at much higher speeds, but these refer to dolphins being pushed along by the bow wave of a speeding boat. They were getting a free ride (their speed relative to the surrounding water was low). It is possible that dolphins can reach speeds over 15 knots during very short bursts (like in preparation for a high jump), but they can't maintain that speed.

sources: D. Au and D. Weihs (1980) At high speeds dolphins save energy by leaping. Nature 284(5756): 548-550

T.M.Williams, W.A.Friedl, J.A. Haun, N.K.Chun (1993) Balancing power and speed in bottlenose dolphins (Tursiops truncatus) in: I.L. Boyd (ed.): Marine Mammals - Advances in behavioral and population biology, pp. 383-394. Symposia of the Zoological Society of London No. 66. Clarendon Press, Oxford

Where can you find dolphins?
Whales and dolphins can be found in almost every sea and ocean, from the Arctic ocean, through the tropics all the way to the Antarctic. Each species however has its own preferred type of habitat. Some live cold water only, others in tropical oceans only. There are also species that can be found in a large variety of environments, like the bottlenose dolphins, killer whales and sperm whales.

source: P.G.H.Evans (1987) The Natural History of Whales and Dolphins. Christoper Helm Publishers, London.

Can dolphins live in fresh water?
There are a number of dolphin species that live in fresh water. They all belong to the river dolphin families. These are: the Platanistidae (Ganges and Indus river dolphins), the Iniidae (the boto or Amazon river dolphin) and the Pontoporiidae (the baiji and the franciscana). There is one species that can be found both in fresh water (the Amazon river) and in coastal sea waters: the tucuxi (Sotalia fluviatilis). In general, salt water species don't do well in fresh water. They can survive for some time, but they will be come exhausted (since they have less buoyancy in fresh water) and after a while their skin will start to slough (like our own skin after spending a long time in the bathtub).

source: P.G.H.Evans (1987) The Natural History of Whales and Dolphins. Christoper Helm Publishers, London.

How do dolphins get their water?
Most dolphins live in the ocean and the ocean water is too salty for them to drink. If they would drink sea water, they would actually use more water trying to get rid of the salt than they drank in the first place. Most of their water they get from their food (fish and squid). Also, when they metabolize (burn) their fat, water is released in the process. Their kidneys are also adapted to retaining as much water as possible. Although they live in water, they have live as desert animals, since they have no direct source of drinkable water.

back to Dolphins