66-641: Marine Mammal Regulations ( MMR ) is a set of rules that govern the taking (fishing, hunting) and treatment of marine mammals in Canada . The regulations are part of the Fisheries Act. The Marine Mammal Regulations s are divided into nine "parts": The "Seal Protection Regulations" were established under the Fisheries Act by the Government of Canada in the mid-1960s. The regulations were combined with other Canadian marine mammals regulations in 1993, into
132-443: A gestation period of 7–8 months, depending on the species. The young are weaned at 1–5 months of age, and reach sexual maturity at 16–17 months. Hyraxes live in small family groups, with a single male that aggressively defends the territory from rivals. Where living space is abundant, the male may have sole access to multiple groups of females, each with its own range. The remaining males live solitary lives, often on
198-405: A blunt snout and reduced dentition rely on suction feeding . Though carnivorous, they house gut flora similar to that of terrestrial herbivores, probably a remnant of their herbivorous ancestry. Baleen whales use their baleen plates to sieve plankton, among others, out of the water; there are two types of methods: lunge-feeding and gulp-feeding. Lunge-feeders expand the volume of their jaw to
264-627: A divergence of the Monachinae (monk seals) and Phocinae lineages 22 mya. Fossil evidence indicates the sea otter ( Enhydra ) lineage became isolated in the North Pacific approximately two mya, giving rise to the now-extinct † Enhydra macrodonta and the modern sea otter, Enhydra lutris . The sea otter evolved initially in northern Hokkaidō and Russia, and then spread east to the Aleutian Islands , mainland Alaska , and down
330-471: A few are specialists. They typically hunt non-schooling fish, slow-moving or immobile invertebrates or endothermic prey when in groups. Solitary foraging species usually exploit coastal waters, bays and rivers. When large schools of fish or squid are available, pinnipeds hunt cooperatively in large groups, locating and herding their prey. Some species, such as California and South American sea lions, may forage with cetaceans and sea birds. The polar bear
396-501: A few eat other mammals. While the number of marine mammals is small compared to those found on land, their roles in various ecosystems are large, especially concerning the maintenance of marine ecosystems, through processes including the regulation of prey populations. This role in maintaining ecosystems makes them of particular concern as 23% of marine mammal species are currently threatened. Marine mammals were first hunted by aboriginal peoples for food and other resources. Many were also
462-698: 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. Marine mammals are adept at thermoregulation using dense fur or blubber , circulatory adjustments ( counter-current heat exchange ); and reduced appendages, and large size to prevent heat loss. Marine mammals are able to dive for long periods. Both pinnipeds and cetaceans have large and complex blood vessel systems pushing large volumes of blood rich in myoglobin and hemoglobin , which serve to store greater quantities of oxygen . Other important reservoirs include muscles and
528-414: A number of primitive mammalian characteristics; in particular, they have poorly developed internal temperature regulation , for which they compensate by behavioural thermoregulation , such as huddling together and basking in the sun. Unlike most other browsing and grazing animals, they do not use the incisors at the front of the jaw for slicing off leaves and grass; rather, they use the molar teeth at
594-438: A number of terrestrial habitats, both continental and island. In temperate and tropical areas, they haul-out on to sandy and pebble beaches, rocky shores , shoals , mud flats , tide pools and in sea caves . Some species also rest on man-made structures, like piers , jetties , buoys and oil platforms . Seals may move further inland and rest in sand dunes or vegetation, and may even climb cliffs. Most cetaceans live in
660-597: A pair of teats, one located close to each of the front flippers. The tusks of hyraxes develop from the incisor teeth as do the tusks of elephants; most mammalian tusks develop from the canines . Hyraxes, like elephants, have flattened nails on the tips of their digits, rather than the curved, elongated claws usually seen on mammals. All modern hyraxes are members of the family Procaviidae (the only living family within Hyracoidea) and are found only in Africa and
726-629: A period of glaciation in the Pleistocene or from the eastern part of Siberia , (from Kamchatka and the Kolym Peninsula). The oldest known polar bear fossil is a 130,000-to-110,000-year-old jaw bone, found on Prince Charles Foreland in 2004. The mitochondrial DNA (mtDNA) of the polar bear diverged from the brown bear roughly 150,000 years ago. Further, some clades of brown bear, as assessed by their mtDNA, are more closely related to polar bears than to other brown bears, meaning that
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#1732793446052792-442: A seal to appear. When the seal exhales, the bear smells its breath, reaches into the hole with a forepaw, and drags it out onto the ice. The polar bear also hunts by stalking seals resting on the ice. Upon spotting a seal, it walks to within 100 yards (90 m), and then crouches. If the seal does not notice, the bear creeps to within 30 to 40 feet (9 to 10 m) of the seal and then suddenly rushes to attack. A third hunting method
858-430: A volume bigger than the original volume of the whale itself by inflating their mouth. This causes grooves on their throat to expand, increasing the amount of water the mouth can store. They ram a baitball at high speeds in order to feed, but this is only energy-effective when used against a large baitball. Gulp-feeders swim with an open mouth, filling it with water and prey. Prey must occur in sufficient numbers to trigger
924-775: Is a tree hyrax living between the Volta and Niger rivers but makes a unique barking call that is distinct from the shrieking vocalizations of hyraxes inhabiting other regions of the African forest zone. The following cladogram shows the relationship between the extant genera: Southern tree hyrax , D. arboreus arboreus Eastern tree hyrax , D. arboreus validus Western tree hyrax , D. dorsalis Benin tree hyrax , D. interfluvialis Yellow-spotted rock hyrax , H. brucei Rock hyrax , P. capensis (extinct hyrax genera; uncertain position) References are made to hyraxes in
990-530: Is herding, where a pod squeezes a school of fish into a small volume, known as a bait ball . Individual members then take turns plowing through the ball, feeding on the stunned fish. Coralling is a method where dolphins chase fish into shallow water to catch them more easily. Killer whales and bottlenose dolphins have also been known to drive their prey onto a beach to feed on it. Killer whales have been known to paralyze great white sharks and other sharks and rays by flipping them upside down. Other whales with
1056-561: Is lower than that of the ungulates . Their mandibular motions are similar to chewing cud , but the hyrax is physically incapable of regurgitation as in the even-toed ungulates and some of the macropods . This behaviour is referred to in a passage in the Bible which describes hyraxes as "chewing the cud". This chewing behaviour may be a form of agonistic behaviour when the animal feels threatened. The hyrax does not construct dens, as most rodents and rodent-like mammals do, but over
1122-418: Is scarce. West Indian manatees eat up to 60 different species of plants, as well as fish and small invertebrates to a lesser extent. Sea otters are a classic example of a keystone species; their presence affects the ecosystem more profoundly than their size and numbers would suggest. They keep the population of certain benthic (sea floor) herbivores, particularly sea urchins , in check. Sea urchins graze on
1188-408: Is the development of echolocation in whales and dolphins. Toothed whales emit a focused beam of high-frequency clicks in the direction that their head is pointing. Sounds are generated by passing air from the bony nares through the phonic lips. These sounds are reflected by the dense concave bone of the cranium and an air sac at its base. The focused beam is modulated by a large fatty organ known as
1254-428: Is the most carnivorous species of bear, and its diet primarily consists of ringed ( Pusa hispida ) and bearded ( Erignathus barbatus ) seals. Polar bears hunt primarily at the interface between ice, water, and air; they only rarely catch seals on land or in open water. The polar bear's most common hunting method is still-hunting: The bear locates a seal breathing hole using its sense of smell, and crouches nearby for
1320-720: Is the only marine mammal that catches fish with its forepaws rather than with its teeth. Under each foreleg, sea otters have a loose pouch of skin that extends across the chest which they use to store collected food to bring to the surface. This pouch also holds a rock that is used to break open shellfish and clams, an example of tool use . The sea otters eat while floating on their backs, using their forepaws to tear food apart and bring to their mouths. Marine otters mainly feed on crustaceans and fish. Pinnipeds mostly feed on fish and cephalopods , followed by crustaceans and bivalves , and then zooplankton and warm-blooded prey (like sea birds ). Most species are generalist feeders, but
1386-437: Is to raid the birth lairs that female seals create in the snow. They may also feed on fish. Sirenians are referred to as "sea cows" because their diet consists mainly of seagrass. When eating, they ingest the whole plant, including the roots, although when this is impossible they feed on just the leaves. A wide variety of seagrass has been found in dugong stomach contents, and evidence exists they will eat algae when seagrass
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#17327934460521452-572: The Eocene . Their evolutionary link to terrestrial mammals was unknown until the 2007 discovery of † Puijila darwini in early Miocene deposits in Nunavut , Canada. Like a modern otter, † Puijila had a long tail, short limbs and webbed feet instead of flippers. The lineages of Otariidae (eared seals) and Odobenidae (walrus) split almost 28 mya. Phocids (earless seals) are known to have existed for at least 15 mya, and molecular evidence supports
1518-618: The Hebrew Bible ( Leviticus 11:5 ; Deuteronomy 14:7 ; Psalm 104:18 ; Proverbs 30:26 ). In Leviticus they are described as lacking a split hoof and therefore not being kosher . It also describes the hyrax as chewing its cud, reflecting its observable ruminant-like mandible motions; the Hebrew phrase in question ( מַעֲלֵה גֵרָה ) means "bringing up cud". Some of the modern translations refer to them as rock hyraxes. ... hyraxes are creatures of little power, yet they make their home in
1584-486: The Indian Ocean . The variation observed in range size is a result of the different ecological requirements of each species and their ability to cope with a broad range of environmental conditions. The high degree of overlap between marine mammal species richness and areas of human impact on the environment is of concern. Most marine mammals, such as seals and sea otters, inhabit the coast. Seals, however, also use
1650-674: The Middle East . In the past, however, hyraxes were more diverse and widespread. At one site in Egypt, the order first appears in the fossil record in the form of Dimaitherium , 37 million years ago, but much older fossils exist elsewhere. For many millions of years, hyraxes, proboscideans, and other afrotherian mammals were the primary terrestrial herbivores in Africa, just as odd-toed ungulates were in North America. Through
1716-551: The North Atlantic right whale , are critically endangered . Other than being hunted, marine mammals can be killed as bycatch from fisheries, where for example they can become entangled in nets 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
1782-551: The North Ronaldsay sheep ( Ovis aries ) which normally eats seaweed outside the lambing season, the Eurasian otter ( Lutra lutra ) which is usually found in freshwater but can be found along coastal Scotland , and others. Marine mammals form a diverse group of 129 species that rely on the ocean for their existence. They are an informal group unified only by their reliance on marine environments for feeding. Despite
1848-574: The Old World (such as cetaceans ). The first known quadrupedal sirenian was † Pezosiren from the early middle Eocene. The earliest known sea cows, of the families † Prorastomidae and † Protosirenidae , were both confined to the Eocene, and were pig-sized, four-legged, amphibious creatures. The first members of Dugongidae appeared by the middle Eocene. At this point, sea cows were fully aquatic. Pinnipeds split from other caniforms 50 mya during
1914-878: The extinct orders Embrithopoda and Desmostylia . The extinct meridiungulate family Archaeohyracidae , consisting of seven genera of notoungulate mammals known from the Paleocene through the Oligocene of South America , is a group unrelated to the true hyraxes. † Seggeurius † Microhyrax † Bunohyrax † Pachyhyrax † Thyrohyrax † Selenohyrax † Saghatherium † Titanohyrax † Antilohyrax † Megalohyrax † Geniohyus ( elephants , mammoths , and mastodons ) ( horses, asses, and zebras ; rhinos ; and tapirs ) † Phenacodontidae Hyracoidea In
1980-522: The hippopotamuses . Sirenians, the sea cows, became aquatic around 40 million years ago. The first appearance of sirenians in the fossil record was during the early Eocene, and by the late Eocene, sirenians had significantly diversified. Inhabitants of rivers, estuaries, and nearshore marine waters, they were able to spread rapidly. The most primitive sirenian, † Prorastomus , was found in Jamaica, unlike other marine mammals which originated from
2046-716: The order Hyracoidea . Hyraxes are well-furred, rotund animals with short tails. Modern hyraxes are typically between 30 and 70 cm (12 and 28 in) in length and weigh between 2 and 5 kg (4 and 11 lb). They are superficially similar to marmots , or over-large pikas , but are much more closely related to elephants and sea cows . Hyraxes have a life span from 9 to 14 years. Both types of "rock" hyrax ( P. capensis and H. brucei ) live on rock outcrops, including cliffs in Ethiopia and isolated granite outcrops called koppies in southern Africa. With one exception, all hyraxes are limited to Africa ;
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2112-643: The spleen which all have the capacity to hold a high concentration of oxygen. They are also capable of bradycardia (reduced heart rate), and vasoconstriction (shunting most of the oxygen to vital organs such as the brain and heart) to allow extended diving times and cope with oxygen deprivation. If oxygen is depleted ( hypoxia ), marine mammals can access substantial reservoirs of glycogen that support anaerobic glycolysis . Sound travels differently through water, and therefore marine mammals have developed adaptations to ensure effective communication, prey capture, and predator detection. The most notable adaptation
2178-602: The "Marine Mammal Regulations". A proposed amendment in 2012 would have required boats to stay at least 50 meters away from belugas in Churchill and Seal River, 400 meters away from threatened or endangered cetaceans (including belugas) in parts of the St. Lawrence, 200 meters from cetaceans in other parts of the St. Lawrence, 100 meters away from cetaceans in other Canadian waters, and 100–300 meters from walruses, though Canada did not expect to add spending for enforcement. The proposal
2244-430: The 'melon'. This acts like an acoustic lens because it is composed of lipids of differing densities. Marine mammals have evolved a wide variety of features for feeding, which are mainly seen in their dentition. For example, the cheek teeth of pinnipeds and odontocetes are specifically adapted to capture fish and squid. In contrast, baleen whales have evolved baleen plates to filter feed plankton and small fish from
2310-429: The 2000s, taxonomists reduced the number of recognized species of hyraxes. In 1995, they recognized 11 species or more. However, as of 2013, only four were recognized, with the others all considered as subspecies of one of the recognized four. Over 50 subspecies and species are described, many of which are considered highly endangered. The most recently identified species is Dendrohyrax interfluvialis , which
2376-497: The Middle East. Their feet have rubbery pads with numerous sweat glands, which may help the animal maintain its grip when quickly moving up steep, rocky surfaces. Hyraxes have stumpy toes with hoof-like nails; four toes are on each front foot and three are on each back foot. They also have efficient kidneys , retaining water so that they can better survive in arid environments. Female hyraxes give birth to up to four young after
2442-528: The North American coast. In comparison to cetaceans, sirenians, and pinnipeds, which entered the water approximately 50, 40, and 20 mya, respectively, the sea otter is a relative newcomer to marine life. In some respects though, the sea otter is more fully adapted to water than pinnipeds, which must haul out on land or ice to give birth. Polar bears are thought to have diverged from a population of brown bears , Ursus arctos , that became isolated during
2508-461: The cetaceans genetically and morphologically fall firmly within the Artiodactyla (even-toed ungulates). 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
2574-510: The course of its lifetime rather seeks shelter in existing holes of great variety in size and configuration. Hyraxes urinate in a designated, communal area. The viscous urine quickly dries and, over generations, accretes to form massive middens. These structures can date back thousands of years. The petrified urine itself is known as hyraceum and serves as a record of the environment, as well as being used medicinally and in perfumes. Hyraxes inhabit rocky terrain across sub-Saharan Africa and
2640-494: The crags; ... The words "rabbit", "hare", "coney", or "daman" appear as terms for the hyrax in some English translations of the Bible. Early English translators had no knowledge of the hyrax, so they didn't give a name for them, though "badger" or "rock-badger" has also been used more recently in new translations, especially in "common language" translations such as the Common English Bible (2011). One of
2706-521: The diversity in anatomy seen between groups, improved foraging efficiency has been the main driver in their evolution . The level of dependence on the marine environment varies considerably with species. For example, dolphins and whales are completely dependent on the marine environment for all stages of their life; seals feed in the ocean but breed on land; and polar bears must feed on land. The cetaceans became aquatic around 50 million years ago (mya). Based on molecular and morphological research,
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2772-424: The exception is the rock hyrax ( P. capensis ) which is also found in adjacent parts of the Middle East . Hyraxes were a much more diverse group in the past encompassing species considerably larger than modern hyraxes. The largest known extinct hyrax, Titanohyrax ultimus , has been estimated to weigh 600–1,300 kilograms (1,300–2,900 lb), comparable to a rhinoceros. Hyraxes retain or have redeveloped
2838-812: The floor or to stay submerged. Surface-living animals (such as sea otters) need the opposite, and free-swimming animals living in open waters (such as 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. Some marine mammals, such as polar bears and otters, have retained four weight-bearing limbs and can walk on land like fully terrestrial animals. All cetaceans are carnivorous and predatory . Toothed whales mostly feed on fish and cephalopods , followed by crustaceans and bivalves . Some may forage with other kinds of animals, such as other species of whales or certain species of pinnipeds . One common feeding method
2904-454: The globe, but their distribution is patchy and coincides with the productivity of the oceans. Species richness peaks at around 40° latitude, both north and south. This corresponds to the highest levels of primary production around North and South America , Africa , Asia and Australia . Total species range is highly variable for marine mammal species. On average most marine mammals have ranges which are equivalent or smaller than one-fifth of
2970-863: The health of coastal ecosystems, and similar changes have been observed as sea otter populations recovered in the Aleutian and Commander Islands and the Big Sur coast of California. However, some kelp forest ecosystems in California have also thrived without sea otters, with sea urchin populations apparently controlled by other factors. The role of sea otters in maintaining kelp forests has been observed to be more important in areas of open coast than in more protected bays and estuaries . Hyrax For extinct genera, see text Hyraxes (from Ancient Greek ὕραξ hýrax ' shrew -mouse'), also called dassies , are small, stout, herbivorous mammals in
3036-529: The ice further north that remains frozen year-round. Seals may also migrate to other environmental changes, such as El Niño , and traveling seals may use various features of their environment to reach their destination including geomagnetic fields, water and wind currents, the position of the sun and moon and the taste and temperature of the water. Baleen whales famously migrate very long distances into tropical waters to give birth and raise young, possibly to prevent predation by killer whales. The gray whale has
3102-576: The longest recorded migration of any mammal, with one traveling 14,000 miles (23,000 km) from the Sea of Okhotsk to the Baja Peninsula . During the winter, manatees living at the northern end of their range migrate to warmer waters. 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
3168-401: The lower stems of kelp , causing the kelp to drift away and die. Loss of the habitat and nutrients provided by kelp forests leads to profound cascade effects on the marine ecosystem. North Pacific areas that do not have sea otters often turn into urchin barrens , with abundant sea urchins and no kelp forest. Reintroduction of sea otters to British Columbia has led to a dramatic improvement in
3234-476: The majority of their time in the water but need to return to land for important activities such as mating , breeding and molting . Sea otters tend to live in kelp forests and estuaries. In contrast, the polar bear is mostly terrestrial and only go into the water on occasions of necessity, and are thus much less adapted to aquatic living. The diets of marine mammals vary considerably as well; some eat zooplankton , others eat fish, squid, shellfish, or seagrass, and
3300-459: The middle to late Eocene , many different species existed. The smallest of these were the size of a mouse but others were much larger than any extant relatives. Titanohyrax could reach 600 kg (1,300 lb) or even as much as over 1,300 kg (2,900 lb). Megalohyrax from the upper Eocene-lower Oligocene was as huge as a tapir. During the Miocene , however, competition from
3366-450: The modern hyrax family. Others appear to have taken to the water (perhaps like the modern capybara ), ultimately giving rise to the elephant family and perhaps also the sirenians. DNA evidence supports this hypothesis, and the small modern hyraxes share numerous features with elephants, such as toenails , excellent hearing, sensitive pads on their feet, small tusks, good memory, higher brain functions compared with other similar mammals, and
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#17327934460523432-538: The newly developed bovids , which were very efficient grazers and browsers, displaced the hyraxes into marginal niches. Nevertheless, the order remained widespread and diverse as late as the end of the Pliocene (about two million years ago) with representatives throughout most of Africa, Europe, and Asia. The descendants of the giant "hyracoids" (common ancestors to the hyraxes, elephants, and sirenians) evolved in different ways. Some became smaller, and evolved to become
3498-541: The oceans, which have also evolved several specialized aquatic traits. In addition to the above, several other mammals have a great dependency on the sea without having become so anatomically specialized, otherwise known as "quasi-marine mammals". This term can include: the greater bulldog bat ( Noctilio leporinus ), the fish-eating bat ( Myotis vivesi ), the arctic fox ( Vulpes lagopus ) which often scavenges polar bear kills, coastal gray wolf ( Canis lupus ) populations which predominantly eat salmon and marine carcasses,
3564-858: The ongoing effects of global warming degrade Arctic environments. Procaviidae Elephantidae Dugongidae (dugongs) Trichechus manatus (West Indian manatee) Trichechus senegalensis (African manatee) Trichechus inunguis (Amazonian manatee; freshwater species) Hippopotamidae Mysticeti (baleen whales) Odontoceti (toothed whales, except river dolphins ) Ruminantia Perissodactyla Pholidota Feliformia Canidae Ursus maritimus (polar bear) all other ursids Enhydra lutris (sea otter) Lontra felina (marine otter) † Neogale macrodon (sea mink) all other mustelids Otariidae (eared seals) Odobenidae (walruses) Phocidae (earless seals) The term "marine mammal" encompasses all mammals whose survival depends entirely or almost entirely on
3630-621: The open ocean, and species like the sperm whale may dive to depths of −1,000 to −2,500 feet (−300 to −760 m) in search of food. Sirenians live in shallow coastal waters, usually living 30 feet (9.1 m) below sea level. However, they have been known to dive to −120 feet (−37 m) to forage deep-water seagrasses . Sea otters live in protected areas, such as rocky shores, kelp forests , and barrier reefs , although they may reside among drift ice or in sandy, muddy, or silty areas. Many marine mammals seasonally migrate. Annual ice contains areas of water that appear and disappear throughout
3696-402: The periphery of areas controlled by larger males, and mate only with younger females. Hyraxes have highly charged myoglobin , which has been inferred to reflect an aquatic ancestry. Hyraxes share several unusual characteristics with mammalian orders Proboscidea (elephants and their extinct relatives) and Sirenia ( manatees and dugongs ), which have resulted in their all being placed in
3762-541: The polar bear might not be considered a species under some species concepts . In general, terrestrial amniote invasions of the sea have become more frequent in the Cenozoic than they were in the Mesozoic. Factors contributing to this trend include the increasing productivity of near-shore marine environments, and the role of endothermy in facilitating this transition. Marine mammals are widely distributed throughout
3828-585: The proposed etymologies for " Spain " is that it may be a derivation of the Phoenician I-Shpania , meaning "island of hyraxes", "land of hyraxes", but the Phoenecian-speaking Carthaginians are believed to have used this name to refer to rabbits, animals with which they were unfamiliar. Roman coins struck in the region from the reign of Hadrian show a female figure with a rabbit at her feet, and Strabo called it
3894-409: The shape of some of their bones . Hyraxes are sometimes described as being the closest living relative of the elephant, although whether this is so is disputed. Recent morphological- and molecular-based classifications reveal the sirenians to be the closest living relatives of elephants. While hyraxes are closely related, they form a taxonomic outgroup to the assemblage of elephants, sirenians, and
3960-497: The side of the jaw. The two upper incisors are large and tusk-like, and grow continuously through life, similar to those of rodents. The four lower incisors are deeply grooved "comb teeth". A diastema occurs between the incisors and the cheek teeth. The dental formula for hyraxes is 1.0.4.3 2.0.4.3 . Although not ruminants , hyraxes have complex, multichambered stomachs that allow symbiotic bacteria to break down tough plant materials, but their overall ability to digest fibre
4026-474: The target for commercial industry, leading to a sharp decline in all populations of exploited species, such as whales and seals. Commercial hunting led to the extinction of the Steller's sea cow , sea mink , Japanese sea lion and Caribbean monk seal . After commercial hunting ended, some species, such as the gray whale and northern elephant seal , have rebounded in numbers; conversely, other species, such as
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#17327934460524092-399: The taxon Paenungulata . Male hyraxes lack a scrotum and their testicles remain tucked up in their abdominal cavity next to the kidneys, as do those of elephants, manatees, and dugongs. Female hyraxes have a pair of teats near their armpits ( axilla ), as well as four teats in their groin (inguinal area); elephants have a pair of teats near their axillae, and dugongs and manatees have
4158-459: The water. Polar bears, otters, and fur seals have long, oily, and waterproof fur in order to trap air to provide insulation. In contrast, other marine mammals—such as whales, dolphins, porpoises, manatees, dugongs, and walruses—have lost long fur in favor of a thick, dense epidermis and a thickened fat layer (blubber) to prevent drag . Wading and bottom-feeding animals (such as manatees) need to be heavier than water in order to keep contact with
4224-409: The whale's interest, be within a certain size range so that the baleen plates can filter it, and be slow enough so that it cannot escape. Otters are the only marine animals that are capable of lifting and turning over rocks, which they often do with their front paws when searching for prey. The sea otter may pluck snails and other organisms from kelp and dig deep into underwater mud for clams . It
4290-483: The year as the weather changes, and seals migrate in response to these changes. In turn, polar bears must follow their prey. In Hudson Bay , James Bay , and some other areas, the ice melts completely each summer (an event often referred to as "ice-floe breakup"), forcing polar bears to go onto land and wait through the months until the next freeze-up. In the Chukchi and Beaufort seas, polar bears retreat each summer to
4356-853: Was still pending in 2015, supported by some environmental groups for western orcas, and opposed by tour operators for Churchill and Seal River belugas, because of different situations in the two areas. Marine mammal Marine mammals are mammals that rely on marine (saltwater) ecosystems for their existence. They include animals such as cetaceans ( whales , dolphins and porpoises ), pinnipeds ( seals , sea lions and walruses ), sirenians ( manatees and dugongs ), sea otters and polar bears . They are an informal group, unified only by their reliance on marine environments for feeding and survival. Marine mammal adaptation to an aquatic lifestyle varies considerably between species. Both cetaceans and sirenians are fully aquatic and therefore are obligate water dwellers. Pinnipeds are semiaquatic; they spend
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