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1.0 - GENERAL BIOLOGY
2.0 - DOLPHIN RESOURCES
3.0 - DOLPHIN TAXONOMY
4.0 AN OVERVIEW OF THE SPECIES OF WHALES AND DOLPHINS
1.0 - GENERAL BIOLOGY
1.1- 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 a 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 behaviour 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
1.2 - 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 generalise (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).
Dolphins have brains as large as humans and have had them for millions of years longer than us. Many scientists agree that if they were not using their brains during this long evolutionary period, dolphins’ brains would have atrophied. Humans have used their brains to change their lifestyle and in doing so have changed the planet. In contrast, dolphins are in total harmony with their environment and probably use their brains to appreciate and enjoy their surroundings. This, some animal behaviourists argue, could make them more intelligent than us - but in a completely different way.
1.3 - How do dolphins communicate and 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 vocalisations are complex enough to support some form of language. However, to date it has not been demonstrated yet that they can undoubtedly communicate among themselves.
1.3a - On the basis that dolphins have large brains and their primary sense is acoustic, Dr. Horace Dobbs has speculated that dolphins send holographic sound images to one another. In his series of books about a fictional dolphin named Dilo, author Horace Dobbs refers to Dilo’s Magic Sound. Thus, when Dilo’s Mother investigates a lobster with her sonar, she mimics the echo when informing her offspring about the lobster. In this way she can pass real information instead of using words which are an abstraction. Thus Dr. Dobbs argues that dolphins have gone beyond language and could be far more advanced than humans when it comes to sonic communication.
1.4 - 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).
1.5 - Can dolphins combine information from their sonar with their vision?
The short answer is: yes, they can. Just like people can visualise 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 (visualisation) 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: 722-7332.
1.6 - What and how much do dolphins eat?
Bottlenose dolphins eat several kinds of fish (including mullet, mackerel, herring, cod) and squid. The compostion 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.
1.7 - 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 expectancy 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. There is, however, anecdotal evidence which indicates that dolphins can live longer than estimated if death by human interference is eliminated from calculations.
1.8 - Do dolphins live shorter in captivity?
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. However, this conclusion could be misleading as many of the early dolphinariums did not record deaths and secretly replaced dolphins if one died, giving the replacement dolphin the same name as its predecessor.
1.9 - How did dolphins evolve?
The earliest recognisable 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. Christopher Helm Publishers, London.
1.10 - How can you interact with wild dolphins?
When swimming, boating or snorkelling 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' behaviour. 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. International Dolphin Watch publishes a world-wide guide on where it is possible to encounter dolphins. This comes free of charge to Friends of IDW, but can be purchase separately.
1.11 - 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 behaviour 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. 129-1882.
1.12 - 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 behaviour 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.1
1.13 - How fast can dolphins swim?
The dolphin's fast cruising speed (a travelling 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 travelling 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 travelling 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 travelling 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 behavioural and population biology, pp. 383-394. Symposia of the Zoological Society of London No. 66. Clarendon Press, Oxford
1.14 - 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. Christopher Helm Publishers, London. Melanie Parker’s ‘At-a-Glance-Guide’, published by IDW, was written to enable those who want to see wild cetaceans, to visit them in their natural habitats.
1.15 - 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. Christopher Helm Publishers, London.
1.16 - 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 to live as desert animals, since they have no direct source of drinkable water.
2.0 - DOLPHIN RESOURCES
2.1 - Where can you find out more about books, videos etc. about dolphins?
There is an excellent list of books, videos and CDs on dolphins, which is put together by Trisha Lamb-Feuerstein. This list is updated on a regular basis. You can find that on the Web at the following URL: http://www.physics.helsinki.fi/whale/literature/biblio.html There is a searchable database at the site of the Dolphin Study Group of the National University of Singapore at: http://dsg.sbs.nus.edu.sg/combib.html. They also have a picture database at: http://dsg.sbs.nus.edu.sg/pictures/
2.1a
International Dolphin Watch (IDW) publishes reviews of books in its journal DOLPHIN, which is sent free to members. IDW also sells a range of books and videos in its Dolphin Shop. These include:
‘Ride a Wild Dolphin’ - a classic video which showed for the first time how a totally free wild dolphin named Donald was interested in interacting with the humans who could scuba dive into his undersea world.
‘The Dolphin Touch’ - a video which shows how experiences with a wild dolphin in the open sea off the coast of Ireland changed the lives of three people with clinical depression, who presented with different symptoms.
The ground breaking case histories of these three patients and others, including Eve Hanf-Enos who is severely autistic, is told by Dr. Horace Dobbs’ book Dolphin Healing (published by Piatkus Books, 2000) which is available from the IDW Dolphin Shop. The Dolphin Shop also sells ‘Dance to a Dolphin’s Song’ (published Jonathan Cape 1990) in which Horace Dobbs tells how a journey into the Australian Aborigine Dolphin Dreamtime led him to the discovery of a Dolphin Pill which is now helping thousands of people with mental problems world-wide.
2.2 - Are there any fictional books starring dolphins?
Yes, there are quite a few. You can find them at the Web site mentioned above.
2.2a
Horace Dobbs has written a series of books about a fictional dolphin, named Dilo, for children. The books also appeal to adults because they are written from a dolphin’s viewpoint and give a wonderful insight into the undersea world as perceived by both humans and dolphins. The books (published by Watch Publishing) include: ‘Dilo and the Call of the Deep’, ‘Dilo Makes Friends’, ‘Dilo and the Treasure Hunters’ and ‘Dilo and the Witch of Black Rock’ (in press) are all available from the Dolphin Shop. The first book Dilo and the Call of the Deep is published in many languages including Dutch, Turkish, Danish, Welsh, Italian, Chinese and Japanese.
Author Horace Dobbs says that Dilo and the Witch of Black Rock is his gift to the children of the world. It is soon to be serialised on this website and can be downloaded free of charge.
2.3 - How can I find dolphin related Web sites?
Most marine mammal Web sites are listed on the Marine Mammal Links page: http://www.rtis.com/nat/user/elsberry/marspec/ms_blem.html This exhaustive list was compiled by Bill Lemus and is now maintained by Wesley Elsberry. Similar information (grouped by category) can be found at: http://www.rtis.com/nat/user/elsberry/marspec.html. Another good starting point is the Aquatic Resources section at the New England Aquarium site at: http://www.neaq.org/.
3.0 - DOLPHIN TAXONOMY
3.1 - How many species of dolphins are there?
The family of dolphins (Delphinidae) consists of 32 different species. Closely related families (the white whales (Monodontidae) 2 species, and river dolphins (Platanistidae) 5 species).
3.2a - What is the dolphin species seen in most oceanaria?
3.2b - What species was the dolphin in the Flipper series?
The bottlenose dolphin (Tursiops truncatus)
3.3 - What is the largest dolphin?
The killer whale (Orcinus orca). The male killer whales can grow up to 9.6 m (31.5 ft).
3.4 - What is the smallest dolphin species?
There is not really one smallest species. The smallest species include: True dolphins (Delphinidae): Tucuxi (Sotalia fluviatilis) - 1.3 to 1.8 m Hector's dolphin (Cephalorhynchus hectori) - 1.2 to 1.5 m Black dolphin (Cephalorhynchus eutropia) - 1.2 to 1.7 m Commerson's dolphin (Cephalorhynchus commersonii) - 1.3 to 1.7 m River dolphins (Platanistidae): Franciscana (Pontoporia blainvillei) - 1.3 to 1.7 m Porpoises (Phocoenidae): Vaquita (Phocoena sinus) - 1.2 to 1.5 m Finless porpoise (Neophocaena phocaenoides) - 1.2 to 1.9 m The tucuxi or Amazon dolphin (Sotalia fluviatilis). These dolphins grow to a maximum of 1.9 m (6.25 ft)
3.5 - What is the difference between dolphins and porpoises?
Dolphins and porpoises belong to different whale families. The most obvious differences are: - dolphins have a falcate (hook-shaped) dorsal fin, whereas porpoises have a triangular dorsal fin. - dolphins have conical teeth; the teeth of of porpoises are spatula shaped. - most dolphin species have a distinct beak. Porpoises don't, giving their head a more rounded, blunt shape.
3.6 - What are cetaceans?
Cetaceans is a collective term for whales, dolphins and porpoises. The name is derived from the scientific (Latin) name of these animals: Cetacea.
3.7 - Are whales and dolphins endangered?
For most species, the answer is probably "No", although it is very difficult to get a good estimate of the size of populations on these water living creatures. A number of species are endangered: the Indus river dolphin, the baiji (there are only about 100 left), the vaquita, the northern right whale and the blue whale. Another group of species is listed as "vulnerable" (which means that they are not in immediate danger of extinction, but also far from safe). These are: the Ganges river dolphin, the boto, the bowhead, the southern right whale, the sei whale, the fin whale and the humpback whale. source: M. Klinowksa (1991) Dolphins, Porpoises and Whales of the World The IUCN Red Data Book IUCN, Gland, Switzerland and Cambridge, UK
Because more people are looking out for dolphins and recording their sitings, it appears that there are more dolphins around. However, the depletion of fish stocks and the accidental capture of dolphins in what is called ‘Bycatch’ is undoubtedly leading to an overall decline in dolphin populations. Indeed it is estimated that dolphins will be virtually eliminated from the North Sea if pair trawling, which is killing hundreds and possibly thousands of dolphins, is allowed to continue.
4.0 An overview of the species of whales and dolphins (the order Cetacea)
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