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Aquatic mammal | Wikipedia audio article

Aquatic mammal | Wikipedia audio article


Aquatic and semiaquatic mammals are a diverse
group of mammals that dwell partly or entirely in bodies of water. They include the various marine mammals who
dwell in oceans, as well as various freshwater species, such as the European otter. They are not a taxon and are not unified by
any distinct biological grouping, but rather their dependence on and integral relation
to aquatic ecosystems. The level of dependence on aquatic life varies
greatly among species. Among freshwater taxa, the Amazonian manatee
and river dolphins are completely aquatic and fully dependent on aquatic ecosystems. Semiaquatic freshwater taxa include the Baikal
seal, which feeds underwater but rests, molts, and breeds on land; and the capybara and hippopotamus
which are able to venture in and out of water in search of food. Mammal adaptation to an aquatic lifestyle
vary considerably between species. River dolphins and manatees are both fully
aquatic and therefore are completely tethered to a life in the water. Seals are semiaquatic; they spend the majority
of their time in the water, but need to return to land for important activities such as mating,
breeding and molting. In contrast, many other aquatic mammals, such
as hippopotamus, capybara, and water shrews, are much less adapted to aquatic living. Likewise, their diet ranges considerably as
well, anywhere from aquatic plants and leaves to small fish and crustaceans. They play major roles in maintaining aquatic
ecosystems, beavers especially. Aquatic mammals were the target for commercial
industry, leading to a sharp decline in all populations of exploited species, such as
beavers. Their pelts, suited for conserving heat, were
taken during the fur trade and made into coats and hats. Other aquatic mammals, such as the Indian
rhinoceros, were targets for sport hunting and had a sharp population decline in the
1900s. After it was made illegal, many aquatic mammals
became subject to poaching. Other than hunting, aquatic mammals can be
killed as bycatch from fisheries, where they become entangled in fixed netting and drown
or starve. Increased river traffic, most notably in the
Yangtze river, causes collisions between fast ocean vessels and aquatic mammals, and damming
of rivers may land migratory aquatic mammals in unsuitable areas or destroy habitat upstream. The industrialization of rivers led to the
extinction of the Chinese river dolphin, with the last confirmed sighting in 2004.==Taxonomy and evolution=====
Groups===This list covers only mammals that live in
freshwater. For a list of saltwater mammals, see Marine
mammal.Order Sirenia: sirenians Family Trichechidae: manatees
Amazonian manatee (Trichechus inunguis) African manatee (Trichechus senegalensis)
Dwarf manatee (Trichechus pygmaeus) validity questionable
Order Cetartiodactyla: even-toed ungulates Suborder Whippomorpha
Family Platanistidae South Asian river dolphin (Platanista gangetica)
with two subspecies Ganges river dolphin, or susu (Platanista
gangetica gangetica) Indus river dolphin, or bhulan (Platanista
gangetica minor) Family Iniidae
Amazon river dolphin, or boto (Inia geoffrensis) Araguaian river dolphin (Inia araguaiaensis)
Family Lipotidae Chinese river dolphin, or baiji (Lipotes vexillifer)
functionally extinct since December 2006 Family Pontoporiidae
La Plata dolphin, or franciscana (Pontoporia blainvillei)
Family Hippopotamidae: hippopotamuses Hippopotamus (Hippopotamus amphibius)
Pygmy hippopotamus (Choeropsis liberiensis) Order Carnivora
Family Mustelidae Subfamily Lutrinae
Eurasian otter (Lutra lutra) Hairy-nosed otter (Lutra sumatrana)
Spotted-necked otter (Hydrictis maculicollis) Smooth-coated otter (Lutrogale perspicillata)
North American river otter (Lontra canadensis) Southern river otter (Lontra provocax)
Neotropical river otter (Lontra longicaudis) Giant otter (Pteronura brasiliensis)
African clawless otter (Aonyx capensis) Oriental small-clawed otter (Aonyx cinerea)
Subfamily Mustelinae European mink (Mustela lutreola)
American mink (Neovison vison) Family Phocidae
Genus Pusa Baikal seal (Pusa sibirica)
Ladoga seal (Pusa hispida ladogensis) Saimaa seal (Pusa hispida saimensis)
Order Rodentia: rodents Suborder Hystricomorpha
Capybara (Hydrochoerus hydrochaeris) Lesser capybara (Hydrochoerus isthmius)
Coypu (Myocastor coypus) Family Castoridae: beavers
North American beaver (Castor canadensis) Eurasian beaver (Castor fiber)
Family Cricetidae Muskrat (Ondatra zibethicus)
European water vole (Arvicola amphibius) Order Monotremata: monotremes
Platypus (Ornithorhynchus anatinus) Order Perissodactyla:odd-toed ungulates
Family Rhinocerotidae: rhinoceroses Javan rhinoceros (Rhinoceros sondaicus)
Indian rhinoceros (Rhinoceros unicornis) Order Afrosoricida
Giant otter shrew (Potamogale velox) Order Soricomorpha
Family Soricidae: shrews Malayan water shrew (Chimarrogale hantu)
Himalayan water shrew (Chimarrogale himalayica) Sunda water shrew (Chimarrogale phaeura)
Japanese water shrew (Chimarrogale platycephala) Chinese water shrew (Chimarrogale styani)
Sumatran water shrew (Chimarrogale sumatrana) Elegant water shrew (Nectogale elegans)
Mediterranean water shrew (Neomys anomalus) Eurasian water shrew (Neomoys fodiens)
Transcaucasian water shrew (Neomys teres) Glacier Bay water shrew (Sorex alaskanus)
American water shrew (Sorex palustris) Pacific water shrew, or marsh shrew (Sorex
bendirii) Family Talpidae (moles and relatives)
Russian desman (Desmana moschata) Order Didelphimorphia: opossums
Family Didelphidae: opossums Lutrine opossum (Lutreolina crassicaudata)
Yapok (Chironectes minimus)===Evolution=======Mesozoic====
One of the first known proto-mammals similar to modern placentals was aquatic, the Jurassic
therapsid Castorocauda. It seems to have been adapted to water much
like a beaver, with teeth different in many ways from all other docodonts, presumably
due to a difference in diet. Most docodonts had teeth specialized for an
omnivorous diet. The teeth of Castorocauda suggest that the
animal was a piscivore, feeding on fish and small invertebrates. The first two molars had cusps in a straight
row, eliminating the grinding function suggesting that they were strictly for gripping and not
for chewing. This feature of three cusps in a row is similar
to the ancestral condition in mammal relatives (as seen in triconodonts), but is almost certainly
a derived character in Castorocauda. These first molars were also recurved in a
manner adapted to hold slippery prey once grasped. These teeth are very similar to the teeth
seen in mesonychids, an extinct group of semi-aquatic carnivorous ungulates, and resemble, to a
lesser degree, the teeth of seals. Another docodontan, the Late Jurassic Haldanodon,
has been suggested to be a platypus or desman-like swimmer and burrower, being well adapted to
dig and swim and occurring in a wetland environment.The tritylodontid Kayentatherium has been suggested
to be semi-aquatic. Unlike Castorocauda and Haldanodon, it was
an herbivore, being probably beaver or capybara-like in habits.Another lineage of Mesozoic mammals,
the eutriconodonts, have been suggested to be aquatic animals with mixed results. Astroconodon occurred abundantly in freshwater
lacustrine deposits and its molars were originally interpreted as being similar to those of piscivorous
mammals like cetaceans and pinnipeds; by extension some researchers considered the possibility
that all eutriconodonts were aquatic piscivores. However, Zofia Kielan-Jaworowska and other
researchers have latter found that the triconodont molars of eutriconodonts were more suited
for a carnassial-like shearing action than the piercing and gripping function of piscivorous
mammal molars, occluding instead of interlocking, and that Astroconodon’s aquatic occurrences
may be of little significance when most terrestrial tetrapod fossils are found in lacustrine environments
anyway.However, two other eutriconodonts, Dyskritodon and Ichthyoconodon, occur in marine
deposits with virtually no dental erosion, implying that they died in situ and are thus
truly aquatic mammals. Nonetheless, Ichthyoconodon may not be aquatic,
but instead a gliding or even flying mammal. More recently, Yanoconodon and Liaoconodon
have been interpreted as semi-aquatic, bearing a long body and paddle-like limbs.A metatherian,
the stagodontid Didelphodon, has been suggested to be aquatic, due to molar and skeleton similarities
to sea otters.====Cenozoic====
An extinct genus, Satherium, is believed to be ancestral to South American river otters,
having migrated to the New World during the Pliocene or early Pleistocene. The South American continent houses the otter
genus Lontra: the giant otter, the neotropical river otter, the southern river otter, and
the marine otter. The smooth-coated otter (Lutrogale perspicillata)
of Asia may be its closest extant relative; similar behaviour, vocalizations, and skull
morphology have been noted.The most popular theory of the origins of Hippopotamidae suggests
that hippos and whales shared a common ancestor that branched off from other artiodactyls
around 60 million years ago (mya). This hypothesized ancestral group likely split
into two branches around 54 mya. One branch would evolve into cetaceans, possibly
beginning about 52 mya, with the protowhale Pakicetus and other early whale ancestors
collectively known as Archaeoceti, which eventually underwent aquatic adaptation into the completely
aquatic cetaceans. The other branch became the anthracotheres,
and all branches of the anthracotheres, except that which evolved into Hippopotamidae, became
extinct during the Pliocene without leaving any descendants. River dolphins are thought to have relictual
distributions, that is, their ancestors originally occupied marine habitats, but were then displaced
from these habitats by modern dolphin lineages. Many of the morphological similarities and
adaptations to freshwater habitats arose due to convergent evolution; thus, a grouping
of all river dolphins is paraphyletic. For example, Amazon river dolphins are actually
more closely related to oceanic dolphins than to South Asian river dolphins. Sirenians, along with Proboscidea (elephants),
group together with the extinct Desmostylia and likely the extinct Embrithopoda to form
the Tethytheria. Tethytheria is thought to have evolved from
primitive hoofed mammals (“condylarths”) along the shores of the ancient Tethys Ocean. Tethytheria, combined with Hyracoidea (hyraxes),
forms a clade called Paenungulata. Paenungulata and Tethytheria (especially the
latter) are among the least controversial mammalian clades, with strong support from
morphological and molecular interpretations. That is, elephants, hyraxes, and manatees
share a common ancestry. The ancestry of Sirenia is distinct from that
of Cetacea and Pinnipedia, although they are thought to have evolved an aquatic lifestyle
around the same time.The oldest fossil of the modern platypus dates back to about 100,000
years ago, during the Quaternary period. The extinct monotremes Teinolophos and Steropodon
were once thought to be closely related to the modern platypus, but more recent studies
show that platypi are more related to the modern echidnas than to these ancient forms
and that at least Teinolophos was a rather different mammal lacking several speciations
seen in platypi. However, the last common ancestor between
platypi and echidnas probably was aquatic, and echidnas thus secondarily became terrestrial. Monotrematum sudamericanum is currently the
oldest aquatic monotreme known. It has been found in Argentina, indicating
monotremes were present in the supercontinent of Gondwana when the continents of South America
and Australia were joined via Antarctica, or that monotremes existed along the shorelines
of Antarctica in the early Cenozoic.===Marine mammals===Marine mammals are aquatic mammals that rely
on the ocean for their existence. They include animals such as sea lions, whales,
dugongs, sea otters and polar bears. Like other aquatic mammals, they do not represent
a biological grouping. s are fully aquatic and therefore are obligate
ocean dwellers. Pinnipeds are semiaquatic; they spend the
majority 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. Likewise, their diet ranges considerably as
well; some may eat zooplankton, others may eat small fish, and a few may eat other mammals. While the number of marine mammals is small
compared to those found on land, their roles in various ecosystems are large. They, namely sea otters and polar bears, play
important roles in maintaining marine ecosystems, especially through regulation of prey populations. Their role in maintaining ecosystems makes
them of particular concern considering 23% of marine mammal species are currently threatened.Marine
mammals were first hunted by aboriginal peoples for food and other resources. They were also the target for commercial industry,
leading to a sharp decline in all populations of exploited species, such as whales and seals. Commercial hunting lead to the extinction
of Steller’s sea cow and the Caribbean monk seal. After commercial hunting ended, some species,
such as the gray whale and northern elephant seal, have rebounded in numbers, however the
northern elephant seal has a genetic bottleneck; conversely, other species, such as the North
Atlantic right whale, are critically endangered. Other than hunting, marine mammals, dolphins
especially, can be killed as bycatch from fisheries, where they become entangled in
fixed netting and drown or starve. Increased ocean traffic causes collisions
between fast ocean vessels and large marine mammals. Habitat degradation also threatens marine
mammals and their ability to find and catch food. Noise pollution, for example, may adversely
affect echolocating mammals, and the ongoing effects of global warming degrades arctic
environments.==Adaptations==
Mammals evolved on land, so all aquatic and semiaquatic mammals have brought many terrestrial
adaptations into the waters. They do not breathe underwater as fish do,
so their respiratory systems had to protect the body from the surrounding water; valvular
nostrils and an intranarial larynx exclude water while breathing and swallowing. To navigate and detect prey in murky and turbid
waters, aquatic mammals have developed a variety of sensory organs: for example, manatees have
elongated and highly sensitive whiskers which are used to detect food and other vegetation
directly front of them, and toothed whales have evolved echolocation.Aquatic mammals
also display a variety of locomotion styles. Cetaceans excel in streamlined body shape
and the up-and-down movements of their flukes make them fast swimmers; the tucuxi, for example,
can reach speeds of 14 miles per hour (23 km/h). The considerably slower sirenians can also
propel themselves with their fluke, but they can also walk on the bottom with their forelimbs. The earless seals (Phocidae) swim by moving
their hind-flippers and lower body from side to side, while their fore-flippers are mainly
used for steering. They are clumsy on land, and move on land
by lunging, bouncing and wiggling while their fore-flippers keep them balanced; when confronted
with predators, they retreat to the water as freshwater phocids have no aquatic predators. Some aquatic mammals have retained four weight-bearing
limbs (e.g. hippopotamuses, beavers, otters, muskrats) and can walk on land like fully
terrestrial mammals. The long and thin legs of a moose limit exposure
to and friction from water in contrast to hippopotamuses who keep most of their body
submerged and have short and thick legs. The semiaquatic pygmy hippopotamus can walk
quickly on a muddy underwater surface thanks to robust muscles and because all toes are
weight-bearing. Some aquatic mammals with flippers (e.g. seals)
are amphibious and regularly leave the water, sometimes for extended periods, and maneuver
on land by undulating their bodies to move on land, similar to the up-and-down body motion
used underwater by fully aquatic mammals (e.g. dolphins and manatees).Beavers, muskrats,
otters, and capybara have fur, one of the defining mammalian features, that is long,
oily, and waterproof in order to trap air to provide insulation. In contrast, other aquatic mammals, such as
dolphins, manatees, seals, and hippopotamuses, have lost their fur in favor of a thick and
dense epidermis, and a thickened fat layer (blubber) in response to hydrodynamic requirements.Wading
and bottom-feeding animals (e.g. moose and manatee) need to be heavier than water in
order to keep contact with the floor or to stay submerged, surface-living animals (e.g.
otters) need the opposite, and free-swimming animals living in open waters (e.g. dolphins)
need to be neutrally buoyant in order to be able to swim up and down the water column. Typically, thick and dense bone is found in
bottom feeders and low bone density is associated with mammals living in deep water.The shape
and function of the eyes in aquatic animals are dependent on water depth and light exposure:
limited light exposure results in a retina similar to that of nocturnal terrestrial mammals. Additionally, cetaceans have two areas of
high ganglion cell concentration (“best-vision areas”), where other aquatic mammals (e.g.
seals, manatees, otters) only have one.Among non-placental mammals, which cannot give birth
to fully developed young, some adjustments have been made for an aquatic lifestyle. The yapok has a backwards-facing pouch which
seals off completely when the animal is underwater, while the platypus deposits its young on a
burrow on land.==Ecology=====
Keystone species===Beaver ponds have a profound effect on the
surrounding ecosystem. Their first and foremost ecological function
is as a reservoir for times of drought, and prevent drying of riverbeds. In the event of a flood, beaver ponds slow
down water-flow which reduces erosion on the surrounding soil. Beaver dams hold sediment, which reduces turbidity
and thereby improving overall water quality downstream. This supplies other animals with cleaner drinking
water and prevents degradation of spawning grounds for fish. However, the slower water speed and lack of
shade from trees (that have since been cut down to construct the dam), results in the
overall temperature increasing. They also house predatory zooplankton which
help break down detritus and control algae populations.===Diet===
Beavers are herbivores, and prefer the wood of quaking aspen, cottonwood, willow, alder,
birch, maple and cherry trees. They also eat sedges, pondweed, and water
lilies. Beavers do not hibernate, but rather they
store sticks and logs in a pile in their ponds, eating the underbark. The dams they build flood areas of surrounding
forest, giving the beaver safe access to an important food supply, which is the leaves,
buds, and inner bark of growing trees. They prefer aspen and poplar, but will also
take birch, maple, willow, alder, black cherry, red oak, beech, ash, hornbeam and occasionally
pine and spruce. They will also eat cattails, water lilies
and other aquatic vegetation, especially in the early spring.Indian rhinoceros are grazers. Their diets consist almost entirely of grasses,
but they also eat leaves, branches of shrubs and trees, fruits, and submerged and floating
aquatic plants. They feed in the mornings and evenings. They use their prehensile lips to grasp grass
stems, bend the stem down, bite off the top, and then eat the grass. They tackle very tall grasses or saplings
by walking over the plant, with legs on both sides and using the weight of their bodies
to push the end of the plant down to the level of the mouth.Manatees make seasonal movements
synchronized with the flood regime of the Amazon Basin. They are found in flooded forests and meadows
during the flood season when food is abundant, and move to deep lakes during the dry season. The Amazonian manatee has the smallest degree
of rostral deflection (25° to 41°) among sirenians, an adaptation to feed closer to
the water surface.A moose’s diet often depends on its location, but they seem to prefer the
new growths from deciduous trees with a high sugar content, such as white birch, trembling
aspen and striped maple, among many others. They also eat many aquatic plants such as
lilies and water milfoil. To reach high branches, a moose may bend small
saplings down, using its prehensile lip, mouth or body. For larger trees a moose may stand erect and
walk upright on its hind legs, allowing it to reach plants 14.0 feet (4.26 m) off the
ground. Moose are excellent swimmers and are known
to wade into water to eat aquatic plants. Moose are thus attracted to marshes and river
banks during warmer months as both provide suitable vegetation to eat and water to bathe
in. Moose have been known to dive underwater to
reach plants on lake bottoms, and the complex snout may assist the moose in this type of
feeding. Moose are the only deer that are capable of
feeding underwater. Hippopotamuses leave the water at dusk and
travel inland, sometimes up to 10 km (6 mi), to graze on short grasses, their main source
of food. They spend four to five hours grazing and
can consume 68 kg (150 lb) of grass each night. Like almost any herbivore, they consume other
plants if presented with them, but their diet consists almost entirely of grass, with only
minimal consumption of aquatic plants. The pygmy hippopotamus emerges from the water
at dusk to feed. It relies on game trails to travel through
dense forest vegetation. It marks trails by vigorously waving its tail
while defecating to further spread its feces. The pygmy hippo spends about six hours a day
foraging for food, and they do not eat aquatic vegetation to a significant extent and rarely
eat grass because it is uncommon in the thick forests they inhabit. The bulk of a pygmy hippo’s diet consists
of ferns, broad-leaved plants and fruits that have fallen to the forest floor. The wide variety of plants pygmy hippos have
been observed eating suggests that they will eat any plants available. This diet is of higher quality than that of
the common hippopotamus.The Amazon river dolphin has the most diverse diet among cetaceans,
consisting of at least 53 species of fish. They mainly feed on croakers, cichlids, tetras,
and piranhas, but they may also target freshwater crabs and river turtles. South Asian river dolphins mainly eat fish
(such as carp, catfish, and freshwater sharks) and invertebrates, mainly prawns.Generally,
all aquatic desmans, shrews, and voles make quick dives and catch small fish and invertebrates. The giant otter shrew, for example, makes
quick dives that last for seconds and grabs small crabs (usually no bigger than 2.8 inches
(7 cm) across). The Lutrine opossum is the most carnivorous
opossum, usually consuming small birds, rodents, and invertebrates. Water voles mainly eat grass and plants near
the water and at times, they will also consume fruits, bulbs, twigs, buds, and roots. However, a population of water voles living
in Wiltshire and Lincolnshire, England have started eating frogs’ legs and discarding
the bodies.==Interactions with humans=====
Exploitation===Fur robes were blankets of sewn-together,
native-tanned, beaver pelts. The pelts were called castor gras in French
and “coat beaver” in English, and were soon recognized by the newly developed felt-hat
making industry as particularly useful for felting. Some historians, seeking to explain the term
castor gras, have assumed that coat beaver was rich in human oils from having been worn
so long (much of the top-hair was worn away through usage, exposing the valuable under-wool),
and that this is what made it attractive to the hatters. This seems unlikely, since grease interferes
with the felting of wool, rather than enhancing it. By the 1580s, beaver “wool” was the major
starting material of the French felt-hatters. Hat makers began to use it in England soon
after, particularly after Huguenot refugees brought their skills and tastes with them
from France.Sport hunting of the Indian rhinoceros became common in the late 1800s and early
1900s. Indian rhinos were hunted relentlessly and
persistently. Reports from the middle of the 19th century
claim that some British military officers in Assam individually shot more than 200 rhinos. By 1908, the population in Kaziranga had decreased
to around 12 individuals. In the early 1900s, the species had declined
to near extinction. Poaching for rhinoceros horn became the single
most important reason for the decline of the Indian rhino after conservation measures were
put in place from the beginning of the 20th century, when legal hunting ended. From 1980 to 1993, 692 rhinos were poached
in India. In India’s Laokhowa Wildlife Sanctuary, 41
rhinos were killed in 1983, virtually the entire population of the sanctuary. By the mid-1990s, poaching had rendered the
species extinct there. In 1950, Chitwan’s forest and grasslands
extended over more than 2,600 km2 (1,000 sq mi) and were home to about 800 rhinos. When poor farmers from the mid-hills moved
to the Chitwan Valley in search of arable land, the area was subsequently opened for
settlement, and poaching of wildlife became rampant. The Chitwan population has repeatedly been
jeopardized by poaching; in 2002 alone, poachers killed 37 animals to saw off and sell their
valuable horns.Otters have been hunted for their pelts since at least the 1700s. There has been a long history of otter pelts
being worn around the world. In China it was standard for the royalty to
wear robes made from them. People that were financially high in status
also wore them. Otters have also been hunted using dogs, specifically
the otterhound. In modern times, TRAFFIC, a joint program
of the World Wildlife Fund (WWF) and International Union for Conservation of Nature (IUCN), reported
that otters are at serious risk in Southeast Asia and have disappeared from parts of their
former range. This decline in populations is due to hunting
to supply the demand for skins.===Habitat degradation===One problem at Lake Baikal is the introduction
of pollutants into the ecosystem. Pesticides such as DDT and hexachlorocyclohexane,
as well as industrial waste, mainly from the Baykalsk Pulp and Paper Mill, are thought
to have been the cause of several disease epidemics among Baikal seal populations. The chemicals are speculated to concentrate
up the food chain and weaken the Baikal seal’s immune system, making them susceptible to
diseases such as canine distemper and the plague, which was the cause of a serious Baikal
seal epidemic that resulted in the deaths of thousands of animals in 1997 and 1999. Baikal seal pups have higher levels of DDT
and PCB than known in any other population of European or Arctic earless seal.In the
1940s, beavers were brought from Canada to the island of Tierra Del Fuego in southern
Chile and Argentina, for commercial fur production. However, the project failed and the beavers,
ten pairs, were released into the wild. Having no natural predators in their new environment,
they quickly spread throughout the island, and to other islands in the region, reaching
a number of 100,000 individuals within just 50 years. They are now considered a serious invasive
species in the region, due to their massive destruction of forest trees, and efforts are
being made for their eradication.In some European countries, such as Belgium, France, and the
Netherlands, the muskrat is considered an invasive pest, as its burrowing damages the
dikes and levees on which these low-lying countries depend for protection from flooding. In those countries, it is trapped, poisoned,
and hunted to attempt to keep the population down. Muskrats also eat corn and other farm and
garden crops growing near water bodies. Urban and agricultural development, increased
damming, and increased use of hydroelectric power in rivers in countries such as Côte
d’Ivoire and Ghana are threats to the African manatee’s habitat and life, and thick congestion
of boats in waterways may cause them to have a deadly run-in with the vessels. However, even natural occurrences, such as
droughts and tidal changes, often strand manatees in an unsuitable habitat. Some are killed accidentally by fishing trawls
and nets intended for catching sharks. The Amazonian manatee is at risk from pollution,
accidental drowning in commercial fishing nets, and the degradation of vegetation by
soil erosion resulting from deforestation. Additionally, the indiscriminate release of
mercury in mining activities threatens the entire aquatic ecosystem of the Amazon Basin.As
China developed economically, pressure on the Chinese river dolphin grew significantly. Industrial and residential waste flowed into
the Yangtze. The riverbed was dredged and reinforced with
concrete in many locations. Ship traffic multiplied, boats grew in size,
and fishermen employed wider and more lethal nets. Noise pollution caused the nearly blind animal
to collide with propellers. Stocks of the dolphin’s prey declined drastically
in the late 20th century, with some fish populations declining to one thousandth of their pre-industrial
levels. In the 1950s, the population was estimated
at 6,000 animals, but declined rapidly over the subsequent five decades. Only a few hundred were left by 1970. Then the number dropped down to 400 by the
1980s and then to 13 in 1997 when a full-fledged search was conducted. On December 13, 2006, the baiji was declared
functionally extinct, after a 45-day search by leading experts in the field failed to
find a single specimen. The last verified sighting was in 2004.===As food===
Moose are hunted as a game species in many of the countries where they are found. While the flesh has protein levels similar
to those of other comparable red meats (e.g. beef, deer and elk), it has a low fat content,
and the fat that is present consists of a higher proportion of polyunsaturated fats
rather than saturated fats. …like tender beef, with perhaps more flavour;
sometimes like veal” Cadmium levels are high in moose liver and
kidneys, with the result that consumption of these organs from moose more than one year
old is prohibited in Finland. Cadmium intake has been found to be elevated
amongst all consumers of moose meat, though the meat was found to contribute only slightly
to the daily cadmium intake. However the consumption of moose liver or
kidneys significantly increased cadmium intake, with the study revealing that heavy consumers
of moose organs have a relatively narrow safety margin below the levels which would probably
cause adverse health effects.In the 17th century, based on a question raised by the Bishop of
Quebec, the Roman Catholic Church ruled that the beaver was a fish (beaver flesh was a
part of the indigenous peoples’ diet, prior to the Europeans’ arrival) for purposes of
dietary law. Therefore, the general prohibition on the
consumption of meat on Fridays did not apply to beaver meat. This is similar to the Church’s classification
of other semi-aquatic rodents, such as the capybara and muskrat.==See also==Aquatic animal
List of semiaquatic tetrapods Marine mammal

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