A marine mammal is one of a number of species that comprise a diverse group of approximately one hundred and thirty different mammal species that live in the world's seas and oceans, or are dependent on them for their survival in the wild. Marine mammals include:

• Cetaceans - Whales, dolphins and porpoises
• Pinnipeds - True seals, Eared seals and Walrus
• Otters - Riverine and marine otters
• Sea cows -  Dugong and Manatees
• Polar bear - the sole marine mammal in family Ursidae

Because of the persistent hunting of many of these species by humans, marine mammals have been undergoing a much higher rate of species extinctions since the mid-Holocene, and continuing into modern times. Other actions of humans such as water pollution, climate change, coastal habitat destruction and habitat fragmentation have added to these species populations declines. While numerous conservation measures to protect marine mammals are underway, dozens of the extant species still remain in various classifications of vulnerability.

Cetaceans

Barnacled Gray whale rostrum at a distance of two meters, San Ignacio Lagoon, Mexico. @ C.Michael Hogan

Aerial view of Cape fur seal colony, Namib Desert coast. @ C.Michael Hogan

Otters

The following genera and species comprise all extant otters:

• European otter, Devonshire, England. Source: Ivan Teage African clawless otter (Aonyx capensis)
• Oriental small-clawed otter (Aonyx cinerea)
• Sea otter (Enhydra lutris)
• Spotted-necked otter (Hydrictis maculicollis)
• North American river otter (Lontra canadensis)
• Marine otter (Lontra felina)
• Southern river otter (Lontra provocax)
• Neotropical river otter (Lontra longicaudis)
• European otter (Lutra lutra)
• Japanese otter (Lutra nippon)  [Some taxonomies place this as a L.lutra subspecies]
• Hairy-nosed otter (Lutra sumatrana)
• Smooth-coated otter (Lutrogale perspicillata)
• Giant otter (Pteronura brasiliensis)-

Sea cows

Sea cows are members of the order Sirenia. While many of the Sea cows have become extinct  in Holocene and somewhat more distant epochs. the extant Sea cows are represented by only two genera:

• Genus Dugong (Monotypic genus with the only species Dugong dugon)
• Genus Trichechus (Taxa: West Indian Manatee (Trichechus manatus), Antillean Manatee (Trichechus manatus manatus), Florida Manatee (Trichechus manatus latirostris),  African Manatee (Trichechus senegalensis), Amazonian Manatee (Trichechus inunguis), Dwarf Manatee (Trichechus pygmaeus), taxon validity in doubt

Polar bear migrating to pack ice, Churchill. @ C.Michael Hogan

Polar bear

The Polar bear (Ursus maritimus) is the only member of the bear family to be classified as a marine mammal, since this species spends a large fraction of its life at sea in the chilly Northern Hemisphere seas. While chiefly a carnivore who feeds at sea, this mammal dens in earth and snow caves and is able to forage terrestrially for birds, small mammals and even plant species, such as dwarf birch and lichens.

Example Conservation Areas

The following are examples of conservation areas having a significant presence of marine mammals with programs of biodiversity protection:

Lady Elliot Island, southernmost cay of the Great Barrier Reef
@ C.Michael Hogan

• Coiba National Park and its Special Zone of Marine Protection, Panama
• Florida Keys National Marine Sanctuary
• Gough Island Wildlife Reserve, United Kingdom
• Great Barrier Reef World Heritage Area, Australia
• Wadi Al-Hitan (Whale Valley), Egypt

Programmatic Protection

The following documents provide insight into the conservation aspects of marine mammals:

• Marine Mammal Protection Act, United States
• Marine Mammal Commission, United States
• Issues Related to the Marine Mammal Protection Act, United States
• Management and conservation of marine mammals and seabirds in the Arctic
• Deepwater Horizon Oil Spill and Marine Mammals

References

• International Whaling Commission. 2000. Report of the Sub-Committee on Small Cetaceans. Journal of Cetacean Research and Management 2: 235-264
• C.Michael Hogan. 2008. Polar Bear: Ursus maritimus, Globaltwitcher.com, ed. Nicklas Stromberg
• Marianne Riedman. 1991. The Pinnipeds: Seals, Sea Lions, and Walruses, University of California Press, ISBN: 0520064984
• Bernd Wursig. 2002. Encyclopedia of Marine Mammals, Academic Press, ISBN: 0125513402
• Marine Mammal Research: Conservation beyond Crisis, edited by John E. Reynolds III, William F. Perrin, Randall R. Reeves, Suzanne Montgomery and Timothy J. Ragen, Johns Hopkins University Press, 2005 ISBN: 0801882559
• Ronald M.Nowak. 1999. Walker's Mammals of the World, Johns Hopkins University Press,  ISBN: 0801857899