Dolphin FAQ (1/3)
Jaap van der Toorn
Posting-Frequency: monthly
Last-modified: 2002/03/14
Maintainer: Jaap van der Toorn <ja...@rosmarus.com>
* This is part 1 of the FAQ for alt.animals dolphins.
* This document is maintained by Jaap van der Toorn
* (ja...@rosmarus.com). The intention is to post the latest
* version of the FAQ on the newsgroup once a month.
*
* Please direct any remarks, suggestions, corrections and
* additions to the above e-mail address.
*
* Last update: March 14, 2002
*
1.0 - What is alt.animals.dolphins?
alt.animals.dolphins is an unmoderated newsgroup for anyone
interested in dolphins. Unmoderated means that no-one is
screening the messages before they are put on the newsgroup.
As a result, you may occassionally see messages on that have
nothing to do with dolphins. Usually these are advertisements
for (often dubious) services and get-rich-fast schemes.
The best way to deal with those is just to ignore them. Do
not post follow-up messages and do not mail to the sender.
This will only encourage them to post more messages in the
future.
Topics that are suitable for this newsgroups include (but
are not restricted to): requests for information, exchanges
of experiences and ideas, news items etc. as long as they
relate to dolphins and/or whales.
Do not post pictures in this newsgroup. These are usually
large and this is not very polite to readers of the group
that have to pay connection time fees. If you want to make
pictures available through Usenet, post them in the designated
newsgroup: alt.binaries.pictures.animals. You can then post
a short announcement in this group that you have made them
available there.
This group is not intended for lengthy discussion on
political issues, even though these may deal with dolphins.
A better platform for these discussions is the newsgroup
talk.politics.animals.
For issues dealing with large whales, there is a separate
newsgroup: alt.animals.whales. Not every provider forwards
its messages, however.
2.0 - GENERAL BIOLOGY
2.1 - 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.
Recent research confirmed that dolphins have only one eye
closed when sleeping. The state (open or closed) of one eye
remains constant for on average an hour, after which it
switches state (Goley, 1999).
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:
P.D. Goley (1999)
Behavioral aspects of sleep in Pacific whitesided dolphins
(Lagenorhynchus obliquidens, Gill 1865)
Marine Mammal Science 15(4): 1054-1064
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 & 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
2.2 - 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 generalize (which is also true of pigs, apes). Also they
can learn to understand complicated language-like commands
(which is also true of the great apes).
Suggested reading:
R.P. Balda, I.M. Pepperberg & A.C. Kamil (eds.) (1998)
Animal cognition in nature - The convergence of psychology
and biology in laboratory and field.
Academic Press, San Diego, London
R.J. Schusterman, J.A. Thomas & F.G. Wood (eds.) (1986)
Dolphin cognition and behavior: a comparative approach,
Lawrence Erlbaum Associates, New Jersey
2.3 - How does the dolphin brain compare to the human brain?
Whales and dolphins have quite large brains. Most authors
agree that the size should be viewed in relation to the body
size. In some comparisons, brain weight to body weight ratio
is used, but it is now more common to use the so-called
Encephalization Quotient (EQ), which is calculated as:
EQ = brain weight / (0.12 * (body weight ^ (2/3)))
(brain weight, divided by 0.12 time the body weight to the
power (2/3)). In this formula, brain and body weight should be
expressed in grammes. In bottlenose dolphins, the EQ lies
between 4 and 5, in the killer whale between 2.5 and 3, in
humans in the 6.5-7.5 range.
However, the structure of the dolphin brain is quite different
from most land mammals and shows a lot of similarities with
so-called archetypal mammals like hedgehogs and bats (mammals in
which the brain structure has changed little since the middle of
the Tertiary period).
Dolphin and whale ancestors returned to the sea 50-70 million years
ago. (Bats have presumably developed their aerial lifestyle in the
same period). In their adaptation to the aquatic environment, they
seem to have retained characteristic features of the brain of the
primitive mammalian species of the time. In cetaceans, the neocortex
has expanded greatly, but without the substantial reorganization
in 6 layers seen in most land mammals. The main features in the
cetacean brain which differ from land mammals are:
- a thin neocortex (about 1.5 mm, compared to 2.9 mm in humans)
- rather uniform structure of the cortex
- low degree of differentiation between cortical layers and cells
- massive development of the (phylogenetically older) layers I and VI
- poor development of layers II, III and IV (which are well developed
in land mammals)
- the neurons have relatively few primary dendrites and these are
weakly branched.
References and suggested reading:
A. Berta & J.L. Sumich (1999)
Marine mammals - Evolutionary biology
Academic Press, San Diego, London
(ch. 7.3 focuses on senses and the nervous system)
I.I. Glezer, P.R. Hof, C. Leranth & P.J. Morgane (1992)
Morphological and histochemical features of odontocete visual
neocortex: immunocytochemical analysis of pyramidal and
non-pyramidal populations of neurons.
in: J.A. Thomas, R.A. Kastelein & A.Y. Supin (eds.):
Marine Mammal Sensory Systems, pp. 1-38
Plenum Press, New York, London
L. Marino (1997)
The relationship between gestation length, encephalization,
and body weight in odontocetes.
Marine Mammal Science 13(1):133-138
P.J. Morgane, M.S. Jacobs & A. Galaburda (1986a)
Evolutionary morphology of the dolphin brain
in: R.J. Schusterman, J.A. Thomas & F.G. Wood (eds.):
Dolphin cognition and behavior: a comparative approach,
pp. 5-29
Lawrence Erlbaum Associates, New Jersey
P.J. Morgane, M.S. Jacobs & A. Galaburda (1986b)
Evolutionary aspects of cortical organization in the
dolphin brain.
in: M.M. Bryden & R. Harrison (eds.):
Research on Dolphins, pp. 71-98
Oxford Science Publications, Clarendon Press, London
P.J. Morgane & I.I. Glezer (1990)
Sensory neocortex in dolphin brain
in: J.A. Thomas & R.A. Kastelein (eds.):
Sensort Abilities of Cetaceas - Laboratory and Field Evidence,
pp, 107-136. NATO ASI Series, Series A: Life Sciences vol. 196
Plenum Press, New York, London
S.H. Ridgway (1986a)
Physological observations on dolphin brains
in: R.J. Schusterman, J.A. Thomas & F.G. Wood (eds.):
Dolphin cognition and behavior: a comparative approach,
pp. 31-59
Lawrence Erlbaum Associates, New Jersey
S.H. Ridgway (1986b)
Dolphin brain size
in: M.M. Bryden & R. Harrison (eds.):
Research on Dolphins, pp. 59-70
Oxford Science Publications, Clarendon Press, London
2.4 - 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 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.
Suggested reading:
R.P. Balda, I.M. Pepperberg & A.C. Kamil (eds.) (1998)
Animal cognition in nature - The convergence of psychology
and biology in laboratory and field.
Academic Press, San Diego, London
R.J. Schusterman, J.A. Thomas & F.G. Wood (eds.) (1986)
Dolphin cognition and behavior: a comparative approach,
Lawrence Erlbaum Associates, New Jersey
2.5 - 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
2.6 - 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 & C. Reichmuth (1995)
Equivalence class formation and cross-modal transfer:
testing marine mammals.
In: R.A. Kastelein, J.A. Thomas & 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 & 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
2.7 - Can dolphins see colors?
To able to see colors, the retina must have at least 2
different kinds of cones, with different sensitivities.
Most mammals have 2 types of cones: L-cones (sensitive to
long-wavelength light, red to green) and S-cones (sentitive
to short-wavelength light, blue to violet or near UV). Humans
and some other primates have 3 types of cones, giving them a
better color vision. Only a few landmammals have only one
type of cone, which means they are colorblind. All these
landmammals are essentially nocturnal animals.
Whales and dolphins (as well as seals and sea lions) have
only one type of cone: the L-cones. Although these cones are
more sensitive for short-wavelength light than the L-cones
of terrestrial mammals, they still have a very low sensitivity
for blue light. And because there is only one type of cone,
they are essentially colorblind (although in theory it is
possible that there is a very limited form of colorvision
in some light conditions, when both the rods and the cones
are active).
Reference:
L. Peichl, G. Behrmann & R.H.H. Kröger (2001)
For whales and seals the ocean is not blue: a visual pigment
loss in marine mammals
European Journal of Neuroscience, vol. 13: 1520-1528
2.8 - 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.
2.9 - 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 & 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
2.10 - Do dolphins live shorter in captivity?
There is no evidence to support that statement.
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 & D.P.DeMaster (1995)
Survival of five species of captive marine mammals.
Marine Mammal Science 11(2):209-226.
2.11 - 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. The closest
relative is probably the hippopotamus (Ursing and Arnason, 1998).
sources:
P.G.H.Evans (1987)
The Natural History of Whales and Dolphins.
Christoper Helm Publishers, London.
B.M. Ursing & U. Arnason (1998)
Analyses of mitochondrial genomes strongly support
a hippopotamus-whale clade
Proceedings of the Royal Society of London B 265: 2251-2255
2.12 - How can you interact with wild dolphins?
When swimming, boating or snorkling 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. Always
check the local regulations for interactions with wildlife!
In several areas there are boat operators that can take you
to areas where there is a good chance to encounter dolphins
(Florida, Bahamas, Hawaii, but also Norway and Iceland).
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.
Also note that there is some evidence that swimming with
wild dolphins may change their behavior (Scarpaci et al, 2001)
Source:
C. Scarpaci, S.W. Bigger, P.J. Corkeron & D. Nugegoda (2001)
Bottlenose dolphins (Tursiops truncatus) increase whistling
in the presence of 'swim-with-dolphin' tour operations
Journal of Cetacean Research and Management 2(3): 183-185
2.13 - 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 occassionally 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, it may be that when the
the group leader is sick and washes ashore, the other members
try to stay close and eventually 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 & D.J. St. Aubin: Biology of marine
mammals: Insights through strandings. Marine Mammal
Commission report no: MMC-77/13: pp. 129-188
2.14 - 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
considarable 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 regulary 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 & 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.
2.15 - 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).
A recent study using based on the vertical speed during
jumps showed maximum speeds for bottlenose dolphins of
8.2-11.2 m/s (16-22 knots, 29.5-40.3 km/hr) prior to a high
jump. The maximum speed for wild bottlenose dolphins was
5.7 m/s (11 knots, 20.5 km/hr) and for common dolphins
6.7 m/s (13 knots, 24.1 km/hr).
sources:
D. Au & D. Weihs (1980)
At high speeds dolphins save energy by leaping.
Nature 284(5756): 548-550
J.J.Rohr, F.E.Fish and J.W. Gilpatrick, Jr. (2002)
Maximum swim speeds of captive and free-rangings
delphinids: critical analysis of extraordinary
performance
Marine Mammal Science 18(1):1-19
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
2.16 - 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 prefered 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.
2.17 - 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.
2.18 - 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.