Marine mammal

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 the oceans, which have also evolved several specialized aquatic traits.

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, 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.

The sea otter evolved initially in northern Hokkaidō and Russia, and then spread east to the Aleutian Islands, mainland Alaska, and down 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 temperate and tropical areas, they haul-out on to sandy and pebble beaches, rocky shores, shoals, mud flats, tide pools and in sea caves.

[44][45][46] Sound travels differently through water, and therefore marine mammals have developed adaptations to ensure effective communication, prey capture, and predator detection.

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.

Prey must occur in sufficient numbers to trigger 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.

[65] 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.

[79] Several animal species, particularly Arctic foxes (Vulpes lagopus) and glaucous gulls (Larus hyperboreus), routinely scavenge polar bear kills.

[41] A decline in Aleutian Islands sea otter populations in the 1990s was controversially attributed by some scientists to killer whale predation, although with no direct evidence.

Initially, moving organisms, such as sharks and hagfish, scavenge soft tissue at a rapid rate over a period of months to as long as two years.

This is followed by the colonization of bones and surrounding sediments (which contain organic matter) by enrichment opportunists, such as crustaceans and polychaetes, throughout a period of years.

[95][96] Japan also harvests several hundred Antarctic and North Pacific minke whales each year, ostensibly for scientific research in accordance with the moratorium.

[100] The scale of seal harvesting decreased substantially after the 1960s,[101] after the Canadian government reduced the length of the hunting season and implemented measures to protect adult females.

Large-scale culling of populations of marine mammals by commercial fishers has been initiated in a number of areas in order to protect fish stocks for human consumption.

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.

[47] For example, extensive shellfish aquaculture takes up valuable space used by coastal marine mammals for important activities such as breeding, foraging and resting.

[47] 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.

[120] A study by evolutionary biologists at the University of Pittsburgh showed that the ancestors of many marine mammals stopped producing a certain enzyme that today protects against some neurotoxic chemicals called organophosphates,[121] including those found in the widely used pesticides chlorpyrifos and diazinon.

Notable organizations include the Greenpeace who focus on overfishing and whaling among other things, and Sea Shepherd Conservation Society who are known for taking direct-action tactics to expose illegal activity.

[137][138] Today, dolphin meat is consumed in a small number of countries worldwide, which include Japan[139][140] and Peru (where it is referred to as chancho marino, or "sea pork").

[141] In some parts of the world, such as Taiji (in Japan) and the Faroe Islands, dolphins are traditionally considered food, and are killed in harpoon or drive hunts.

[142] The Faroe Islands population was exposed to methylmercury largely from contaminated pilot whale meat, which contained very high levels of about 2 mg methylmercury/kg.

The study of about 900 Faroese children showed that prenatal exposure to methylmercury resulted in neuropsychological deficits at 7 years of ageRinged seals were once the main food staple for the Inuit.

Captive life is also stressful due to the requirement to perform circus tricks that are not part of wild killer whale behavior, as well as restricting pool size.

They also oppose using sea lions for entertainment, claiming the tricks performed are "exaggerated variations of their natural behaviors" and distract the audience from the animal's unnatural environment.

[170] Bottlenose dolphins and California sea lions are used in the United States Navy Marine Mammal Program (NMMP) to detect mines, protect ships from enemy soldiers, and recover objects.

The sea lion team retrieved test equipment such as fake mines or bombs dropped from planes usually out of reach of divers who would have to make multiple dives.

The Navy states that this is to prevent them from ingesting harmful objects, but conservation activists say this is done to reinforce the trainers' control over the dolphins, who hand out food rewards.

A humpback whale swimming
A humpback whale ( Megaptera novaeangliae )
A black-speckled seal with a light-gray underside and a dark-gray back, sitting on rocks, its mouth agape showing sharp teeth
A leopard seal ( Hydrurga leptonyx )
A furry, streamlined mammal swimming through the water with toes visible on each foot, similar to those of an elephant. All limbs are thrust backwards or underneath the animal.
Illustration of † Prorastomus , an early sirenian (40 mya)
Marine mammal species richness: A) All species (n = 115), B) toothed whales (n = 69), C) baleen whales (n = 14), D) seals (n = 32), based on data from 1990 to 1999 [ 31 ]
The labelled, anatomy of a dolphin showing its skeleton, major organs, and shape of the body
A killer whale sticking the front end of its body out of the water onto a floating piece of sea-ice to grab a dark-brown seal with light-brown-spots
Killer whale hunting a Weddel seal
A sea otter floating on the water on its back holding a sea urchin with one hand and a rock in the other
Sea otters have dexterous hands which they use to smash sea urchins off rocks
A dugong with its mouth on the sandy seafloor, leaving a noticeable cloud which hovers near the bottom. There are two yellow fish with black stripes near its mouth, and there are grasses poking out of the seafloor
A dugong feeding on the sea-floor
Fish and phytoplankton bring nutrients to the seafloor in the form of detritus, and whales bring nutrients up to the surface also in the form of detritus.
"Whale pump" – the role played by whales in recycling ocean nutrients [ 90 ]
A group of seal hunters surround a small group of sea lions with their clubs in the air
Men killing northern fur seals on Saint Paul Island , Alaska, in the 1890s
Alaskan sea otters inhabit most of the Aleutian Islands and the Pacific Northwest, Asian sea otters inhabit the islands around Kamchatka Peninsula and those that stretch between there and Japan (excluding in the Sea of Okhosk) and California sea otters inhabit the coast of southern California. Their former range follows the coast of southern California north, into the Aleutian Islands, without any gaps in between.
Historical and modern range of northern sea otters
A right whale sliced on both sides after colliding with a boat. A large amount of its flesh is visible as well as the intestines floating in the water
The remains of a North Atlantic right whale after it collided with a ship propeller
The Canadian Basin is blue for the most part, while the rest of the Arctic Basin is mainly red with scattered areas of blue
Map from the U.S. Geological Survey shows projected changes in polar bear habitat from 2005 to 2095. Red areas indicate loss of optimal polar bear habitat; blue areas indicate gain.
Signatory countries of the International Whaling Commission (IWC)
An adult and sub-adult Minke whale are dragged aboard the Nisshin Maru , a Japanese whaling vessel
The whale meat is dark purple and shredded like jerky, the blubber is a pale-pink color and in slices, the dried fish is a light-brown color and ripped into slices, and the potatoes are light-yellow and cut into thin slices.
Pilot whale meat (bottom), blubber (middle) and dried fish (left) with potatoes, Faroe Islands
A killer whale with a collapsed dorsal fin breaching out of a pool in front of an audience in stands
Performing killer whale at SeaWorld San Diego , 2009
A grey sea lion with white whiskers balancing a ball that resembles a blue-and-red basketball
A sea lion trained to balance a ball on its nose
A bottlenose dolphin jumping out of the water (the entire body is visible) in front of a trainer in camouflage. The dolphin is wearing a small, cylindrical camera on its right fin
A dolphin wearing a locating pinger, performing mine clearance work in the Iraq War