Marine mammal
jority of their time in the water, but need to return to
land for important activities such as mating, breeding and
molting. In contrast, both otters and the polar bear are
much less adapted to aquatic living.[2] While the number
of marine mammals is small compared to those found
on land, their total biomass is large. They play important roles in maintaining marine ecosystems, especially
through regulation of prey populations.[3] These two factors make them an integral component of the marine environment. This is of particular concern considering 23%
of marine mammal species are currently threatened.[4]
A humpback whale (Megaptera novaeangliae), a member of order Cetacea
1 Taxonomy
A leopard seal (Hydrurga leptonyx), a member of suborder
Pinnipedia of order Carnivora
Marine mammals, which include seals, whales,
dolphins, porpoises, manatees, dugongs, marine otters,
walruses, and polar bears, form a diverse group of 129
species that rely on the ocean for their existence.[1]
They do not represent a distinct biological grouping,
but rather are unified by their reliance on the aquatic
environment for feeding.[2] The level of dependence on
the aquatic environment for existence varies considerably
with species. For example, dolphins and whales are
completely dependent on the marine environment for all
stages of their life, whereas seals feed in the ocean, but
breed on land.[2]
A polar bear (Ursus maritimus), a member of family Ursidae
Mammals have returned to the water in at least
nine separate evolutionary lineages: Cetacea, Sirenia,
Desmostylia, Pinnipedia, Ursus maritimus (polar bear),
Kolponomos (marine bear), Thalassocnus (aquatic sloth),
Enhydra lutris (sea otter) and Lontra feline (marine
otter); the eutriconodont Ichthyoconodon might have
also been marine in habits. Four of these lineages
are extinct (Desmostylia; Kolponomos; Thalassocnus,
Ichthyoconodon).[1] Despite the diversity in morphology
seen between groups, improving foraging efficiency has
been the main driver in the evolution in these lineages.[5]
Today, marine mammals belong to one of three orders:
Cetartiodactyla, Sirenia, or Carnivora.
Marine mammals can be subdivided into four recognised
groups; cetaceans (whales, dolphins, and porpoises),
pinnipeds (seals, sea lions and walruses), sirenians
(manatees and dugongs), and fissipeds, which are the
group of carnivores with separate digits (the polar
bear, and two species of otter). Both cetaceans and
sirenians are fully aquatic and therefore are obligate ocean Based on molecular and morphological research, the
dwellers. Pinnipeds are semiaquatic; they spend the ma- cetaceans genetically and morphologically fall firmly
1
2
2
DIVERSITY, DISTRIBUTION AND HABITAT
• Family Eschrichtiidae (gray whale) = 1
species
• Odontoceti (toothed whales)
• Family Physeteridae (sperm whale) = 1
species
• Family Kogiidae (pygmy and dwarf
sperm whales = 1 genus; 2 species
• Family Monodontidae (narwhal and beluga) = 2 genera; 2 species
• Family Ziphiidae (beaked whales) = 6
genera; 21 species
• Family Delphinidae (oceanic dolphins) =
17 genera; 38 species
• Family Phocoenidae (porpoises) = 2 genera; 7 species
• Family Platanistidae (South Asia river
dolphin) = 1 species
• Family Iniidae (boto) 1 species
• Family Pontoporiidae (franciscana) = 1
species
A sea otter (Enhydra lutris), a member of family Mustelidae
within the Artiodactyla (even-toed ungulates).[6][7] The
term Cetartiodactyla reflects the idea that whales evolved
within the ungulates. The term was coined by merging the
name for the two orders, Cetacea and Artiodactyla, into a
single word. Under this definition, the closest living land
relative of the whales and dolphins is thought to be the
hippopotamuses. Use of Order Cetartiodactyla, instead
of Cetacea with Suborders Odontoceti and Mysticeti,
is favored by most evolutionary mammalogists working with molecular data[8][9][10][11] and is supported the
IUCN Cetacean Specialist Group[12] and by Taxonomy
Committee[13] of the Society for Marine Mammalogy,
the largest international association of marine mammal
scientists in the world. Some others, including many marine mammalogists and paleontologists, favor retention of
Order Cetacea with the two suborders in the interest of
taxonomic stability.
Within the Order Sirenia are the manatees and the
dugongs.
Order Carnivora contains the pinnipeds
(sealions, walruses and seals), the polar bear (Ursus maritimus), and the two otters (Enhydra lutris and Lontra feline).[2]
1.1
• Order Sirenia (sea cows)
•
• Family Trichechidae (manatees) = 1
genus; 3 species
• Family Dugongidae (dugongs) = 1 species
• Order Carnivora (carnivores):
•
• Family Mustelidae = 2 genera; 2 species
• Family Ursidae (bears) = 1 species, Ursus
maritimus (polar bear)
• Suborder Pinnipedia (sealions,
seals)
walruses,
• Family Otariidae (eared seals and sea lions) = 7 genera; 15 species
• Family Odobenidae (walrus) = 1 species
• Family Phocidae (true seals) = 14 genera;
18 species
Classification of living species
Further information: List of marine mammal species
• Order Cetartiodactyla[13]
2 Diversity, distribution and habitat
Marine mammals are widely distributed throughout the
globe, but their distribution is patchy and coincides with
• Cetacea (unranked)
the productivity of the oceans.[14] Species richness peaks
at around 40° latitude, both north and south. This corre• Mysticeti (baleen whales)
sponds to the highest levels of primary production around
• Family Balaenidae (right and bowhead
North and South America, Africa, Asia and Australia.
whales) = 2 genera; four species
Total species range is highly variable for marine mam• Family Neobalaenidae (pygmy right mal species. On average most marine mammals have
whale) = one species
ranges which are equivalent or smaller than one-fifth of
• Family Balaenopteridae (rorquals) = 2 the Indian Ocean.[4] The variation observed in range size
genera; 8 species
is a result of the different ecological requirements of each
3
they are constantly losing water to the surrounding environment. They have evolved a number of mechanisms to
overcome this, but most retain their water by using highly
efficient kidneys, that can concentrate urine.[14] Marine
mammals are able to dive for long periods of time. Both
pinnipeds and cetaceans have large and complex blood
vessel systems which serve to store oxygen to support
deep diving. Other important reservoirs include muscles,
blood, and the spleen which all have the capacity to hold
a high concentration of oxygen. Other features include
bradycardia (reduced heart rate), and vasoconstriction
(shunts most of the oxygen to vital organs such as the
brain and heart) also assist with extended diving and oxygen deprivation.[14]
Bottlenose dolphin at Dolphin Reef, Eilat, Israel
If oxygen is depleted, marine mammals can access substantial reservoirs of glycogen that support anaerobic glycolysis
of the cells involved during conditions of systemic
species and their ability to cope with a broad range of enhypoxia
associated with prolonged submersion.[15][16][17]
vironmental conditions. There is a high degree of overlap
between marine mammal species richness and areas of Sound travels differently through water therefore mahuman impact on the environment which is of concern.[3] rine mammals have developed a number of ways to ensure effective communication, prey capture, and predator
detection.[18] The most notable adaptation is the development of echolocation in whales and dolphins.[14] Lastly,
3 Anatomy and physiology
Marine mammals have evolved a number features for
feeding, which are mainly seen in their dentition. For example, the cheek teeth of pinniped and odontocetes are
designed specifically to capture fish and squid. In contrast, Mysticetes have evolved baleen plates to filter feed
plankton and small fish from the water.[14]
4 Threats
Illustration of the oceanic whale pump that moves nutrients
through the water column
Marine mammals have a number of physiological and
anatomical features to overcome the unique challenges
associated with aquatic living. Some of these features
are very species specific. Marine mammals have developed a number of features for efficient locomotion such
as torpedo shaped bodies to reduce drag; modified limbs
for propulsion and steering; tail flukes and dorsal fins for
propulsion and balance.[14] Marine mammals are adept
at thermoregulation using dense fur or blubber to reduce
heat loss; as well as circulatory adjustments to conserve
their body temperature (counter-current heat exchangers); torpedo shaped bodies, reduced appendages, and
large size to prevent heat loss.[14]
A West Indian manatee (Trichechus manatus), a member of order Sirenia
4.1 Exploitation
Marine mammals were hunted by coastal aboriginal humans historically for food and other resources. These
subsistence hunts occur in Canada, Greenland, Indonesia,
Most marine mammals are hypoosmotic and as a result Russia, the United States, and several nations in the
4
4 THREATS
also harvests several hundred Antarctic and North Pacific minke whales each year under the guise of scientific
research.[19] However, the illegal trade of whale and dolphin meat is a significant market in some countries.[22]
Seals and sealions are also still hunted commercially in
some countries, including Canada, Greenland, Iceland,
Norway, Russia, Finland and Sweden.
4.2 By-catch
California sea lions, members of the family Otariidae.
Further information: Cetacean bycatch
By-catch is the incidental capture of non-target species
in fisheries. Fixed and drift gill nets cause the highest mortality levels for both cetaceans and pinnipeds,
however, entanglements in long lines, mid-water trawls,
and both trap and pot lines are also common.[23] Tuna
seines are particularly problematic for entanglement by
dolphins.[24] By-catch affects all cetaceans, both small
and big, in all habitat types. However, smaller cetaceans
and pinnipeds are most vulnerable as their size means
that escape once they are entangled is highly unlikely and
they frequently drown.[19] While larger cetaceans are capable of dragging nets with them, the nets sometimes remain tightly attached to the individual and can impede the
Desmostylus (extinct)
animal from feeding sometimes leading to starvation.[19]
Abandoned or lost nets and lines cause mortality through
ingestion or entanglement.[25] Marine mammals also get
Caribbean. Under the terms of the 1986 moratorium on entangled in aquaculture nets, however, these are rare
whaling, the International Whaling Commission (IWC) events and not prevalent enough to impact populations.[26]
allows whaling carried out by aboriginal groups if it occurs on a subsistence basis; however hunts in Canada
and Indonesia are conducted outside the authority of the 4.3 Vessel strikes
IWC. The effects of these are only localised, as hunting efforts were on a relatively small scale.[14] Later, Vessel strikes cause death for a number of marine mamcommercial hunting was developed and marine mammals mals, especially whales.[19] In particular, fast commerwere heavily exploited. This led to the extinction of the cial vessels such as container ships can cause major inSteller’s Sea Cow and the Caribbean monk seal.[14] To- juries or death when they collide with marine mammals.
day, populations of species that were historically hunted, Collisions occur both with large commercial vessels and
such as blue whales (Balaenoptera musculus musculus and recreational boats and cause injury to whales or smaller
B. m. brevicauda), and the North Pacific right whale (Eu- cetaceans. The critically endangered northern right whale
balaena japonica), are much lower compared to their pre- is particularly affected by vessel strikes. Tourism boats
exploited levels.[19] Because whales generally have slow designed for whale and dolphin watching can also neggrowth rates, are slow to reach sexual maturity, and have atively impact on marine mammals by interfering with
a low reproductive output, population recovery has been their natural behavior.[27]
very slow.[18]
Despite the fact commercial whaling is generally a thing
of the past since the passage of the International Whaling Commission’s moratorium on commercial whaling,
a number of marine mammals are still subject to direct
hunting. There are only two nations remaining which
sanction commercial whaling: Norway, where several
hundred northeastern North Atlantic minke whales are
harvested each year; and Iceland, were quotas of 150
fin whales and 100 minke whales per year are set under
objection to an ongoing moratorium established by the
International Whaling Commission in 1986.[20][21] Japan
4.4 Habitat loss and degradation
Habitat degradation is caused by a number of human
activities. Marine mammals that live in coastal environments are most likely to be affected by habitat
degradation and loss. Developments such as sewage
marine outfalls, moorings, dredging, blasting, dumping,
port construction, hydroelectric projects, and aquaculture
both degrade the environment and take up valuable
habitat.[18] For example, extensive shellfish aquaculture
4.8
Global climate change
5
takes up valuable space used by coastal marine mammals activities, construction and oceanographic or geophysical
for important activities such as breeding, foraging and research. They can cause injuries such as hemorrhagresting.[26]
ing of the lungs, and contusion and ulceration of the
gastrointestinal tract.[19] Underwater noise is generated
from shipping, the oil and gas industry, research, and
4.5 Competition/conflict with fisheries
military use of sonar and oceanographic acoustic experimentation. Acoustic harassment devices and acoustic
The fishery industry not only threatens marine mammals deterrent devices used by aquaculture facilities to scare
through by-catch, but also through competition for food. away marine mammals emit loud and noxious underwaLarge scale fisheries have led to the depletion of fish ter sounds.[26]
stocks that are important prey species for marine mammals. Pinnipeds have been especially affected by the direct loss of food supplies and in some cases the harvesting 4.8 Global climate change
of fish has led to food shortages or dietary deficiencies,[28]
starvation of young, and reduced recruitment into the Main article: Effects of climate change on marine
population.[29] As the fish stocks have been depleted, the mammals
competition between marine mammals and fisheries has
sometimes led to conflict. Large-scale culling of populations of marine mammals by commercial fishers has Two changes to the global atmosphere due to
been initiated in a number of areas in order to protect anthropogenic activity threaten marine mammals.
The first is increases in ultraviolet radiation due to ozone
fish stocks for human consumption.[30]
depletion, and this mainly affects the Antarctic and
other areas of the southern hemisphere.[18] An increase
4.6 Competition/conflict with aquaculture in ultraviolet radiation has the capacity to decrease
phytoplankton abundance, which forms the basis of
[33]
The second effect of
Shellfish aquaculture takes up space so in effect cre- the food chain in the ocean.
global
climate
change
is
global
warming
due to increased
ates competition for space. However, there is little di[26]
carbon
dioxide
levels
in
the
atmosphere.
Raised sea levrect competition for aquaculture shellfish harvest. On
els,
sea
temperature
and
changed
currents
are expected
the other hand, marine mammals regularly take finfish
to
affect
marine
mammals
by
altering
the
distribution
from farms, which creates significant problems for maof
important
prey
species,
and
changing
the
suitability
rine farmers. While there are usually legal mechanisms
[34]
of
breeding
sites
and
migratory
routes.
The
Arctic
designed to deter marine mammals, such as anti-predator
food
chain
would
be
disrupted
by
the
near
extinction
nets or harassment devices, individuals are often illegally
or migration of polar bears. Arctic sea ice is the polar
shot.[26]
bear’s habitat. It has been declining at a rate of 13% per
decade because the temperature is rising at twice the
rate of the rest of the world.[35] By the year 2050, up to
4.7 Pollution
two-thirds of the world’s polar bears may vanish if the
sea ice continues to melt at its current rate.[36]
Further information: Marine mammals and sonar
Contaminants that are discharged into the marine environment accumulate in the bodies of marine mammals when they are stored unintentionally in their blubber
along with energy.[18] Contaminants that are found in the
tissues of marine mammals include heavy metals, such as
mercury and lead, but also organochlorides and polycyclic
aromatic hydrocarbons.[18] For example, these can cause
disruptive effects on endocrine systems;[25] impair the reproductive system, and lower the immune system of individuals, leading to a higher number of deaths.[18] Other
pollutants such as oil, plastic debris and sewage threaten
the livelihood of marine mammals.[31]
Noise pollution from anthropogenic activities is another
major concern for marine mammals. This is a problem because underwater noise pollution interferes with
the abilities of some marine mammals to communicate,
and locate both predators and prey.[32] Underwater explosions are used for a variety of purposes including military
5 See also
• Aquatic mammal
• Aquatic animal
• Marine mammals as food
• U.S. Navy Marine Mammal Program
6 References
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6
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[33] Madronich, S.; McKenzie, R. L.; Björn, L. O.; Caldwell,
M. M. (1998). “Changes in biologically active ultraviolet radiation reaching the Earth’s surface”. Journal of
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[35] “Arctic Sea Ice | NRDC”. www.nrdc.org. Retrieved
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[36] A Bayesian Network Modeling Approach to Forecasting
the 21st Century Worldwide Status of Polar Bears
7
Other references
• Perrin WF, Wursig B and Thewissen JGM (2009)
Encyclopedia of Marine Mammals Academic Press.
ISBN 9780080919935.
8 External links
• The Society for Marine Mammalogy The largest organization of marine mammalogists in the world.
• Introduction to the Desmostylia Museum of Paleontology, University of California – extinct group of
marine mammals
8
9 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES
9
Text and image sources, contributors, and licenses
9.1
Text
• Marine mammal Source: https://en.wikipedia.org/wiki/Marine_mammal?oldid=697344232 Contributors: AxelBoldt, Andre Engels, Graham, Pcb21, Bueller 007, Glenn, Zarius, Phoebe, Robbot, Nurg, Pingveno, Arnejohs, Gadfium, Pgan002, Antandrus, Icairns, Syvanen,
AliveFreeHappy, Vsmith, ESkog, Neg, Pharos, Alansohn, Inky, Snowolf, Danhash, Gene Nygaard, Wevets, BD2412, Rjwilmsi, Nihiltres,
Chobot, Elaphe1011, Wavelength, RussBot, Stephenb, NawlinWiki, Brian Crawford, Daniel Mietchen, Epipelagic, BorgQueen, Luk, Yamaguchi , Skizzik, Miquonranger03, MalafayaBot, J. Spencer, Salmar, Eliezg, Edivorce, TobiWanKenobi~enwiki, BullRangifer, Bogsat,
Anlace, Mircea, Scientizzle, Mgiganteus1, Wickethewok, Shangrilaista, Ryulong, JMK, Gil Gamesh, Gilabrand, JForget, RagingR2, Reywas92, Clayoquot, Gogo Dodo, JamesAM, Thijs!bot, Epbr123, Mojo Hand, Seaphoto, [email protected], Mattjuge, Hut 8.5, Papa Lima
Whiskey, DeniseB, Acroterion, WolfmanSF, Stuart Morrow, Soulbot, Jvhertum, NatureA16, MartinBot, GimliDotNet, R'n'B, J.delanoy,
SiliconDioxide, Wayne Gloege, WarFox, Mike V, Dancor, Metalraptor, CardinalDan, Barneca, Philip Trueman, TXiKiBoT, LeaveSleaves,
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9.2
Images
• File:Desmostylus2DB.jpg Source: https://upload.wikimedia.org/wikipedia/commons/a/af/Desmostylus2DB.jpg License: CC BY 3.0
Contributors: [email protected] Original artist: Dmitry Bogdanov
• File:Estuary-mouth.jpg Source: https://upload.wikimedia.org/wikipedia/commons/b/b2/Estuary-mouth.jpg License: Public domain
Contributors: ? Original artist: ?
• File:FL_fig04.jpg Source: https://upload.wikimedia.org/wikipedia/commons/6/6f/FL_fig04.jpg License: Public domain Contributors:
Photo from U.S. Geological Fact Sheet 010-99; FS-010-99 Original artist: U.S. Department of the Interior, U.S. Geological Survey
• File:Humpback_Whale_underwater_shot.jpg Source: https://upload.wikimedia.org/wikipedia/commons/6/61/Humpback_Whale_
underwater_shot.jpg License: Public domain Contributors: ? Original artist: ?
• File:Hydrurga_leptonyx_edit1.jpg Source: https://upload.wikimedia.org/wikipedia/commons/b/bf/Hydrurga_leptonyx_edit1.jpg License: CC-BY-SA-3.0 Contributors: ? Original artist: ?
• File:Maldivesfish2.jpg Source: https://upload.wikimedia.org/wikipedia/commons/3/35/Maldivesfish2.jpg License: CC BY-SA 2.0 Contributors: Originally uploaded to Flickr as Fishes Original artist: Betty x1138
• File:Oceanic_whale_pump_-_journal.pone.0013255.g001.tiff Source:
https://upload.wikimedia.org/wikipedia/commons/9/96/
Oceanic_whale_pump_-_journal.pone.0013255.g001.tiff License: CC BY 2.5 Contributors: From: The Whale Pump: Marine
Mammals Enhance Primary Productivity in a Coastal Basin. PLoS ONE 5(10): e13255. doi:10.1371/journal.pone.0013255
url-http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0013255 Original artist: Roman J and McCarthy JJ
• File:PikiWiki_Israel_15217_Dolphin.JPG Source: https://upload.wikimedia.org/wikipedia/commons/7/75/PikiWiki_Israel_15217_
Dolphin.JPG License: CC BY 2.5 Contributors: Ronen Marcus via the PikiWiki - Israel free image collection project Original artist:
‫רונן מרקוס‬
• File:Sea_lion_family.JPG Source: https://upload.wikimedia.org/wikipedia/commons/f/f5/Sea_lion_family.JPG License: Public domain
Contributors: Transferred from en.wikipedia
Original artist: Intothewoods29 (talk). Original uploader was Intothewoods29 at English Wikipedia
• File:Sea_otter_cropped.jpg Source: https://upload.wikimedia.org/wikipedia/commons/1/15/Sea_otter_cropped.jpg License: CC BY 2.0
Contributors: sea-otter-mom-and-pup_06 Original artist: Mike Baird from Morro Bay, USA
• File:Ursus_maritimus_4_1996-08-04.jpg Source:
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1996-08-04.jpg License: CC BY-SA 2.5 Contributors: photo taken by Ansgar Walk Original artist: Ansgar Walk
9.3
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