MSD Manual

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Professional Version

Overview of Marine Mammals


Cara L. Field

, DVM, PhD, DACZM, Marine Mammal Center, Sausalito, CA

Reviewed/Revised Jun 2022 | Modified Oct 2022

Marine mammals are a diverse group of species found worldwide that include cetaceans, pinnipeds, sirenians, sea otters, and polar bears.

The order Cetacea consists of two major suborders with different physiology and anatomy:

  • Odontocetes (toothed whales)

  • Mysticetes (baleen whales)

Within order Carnivora are the pinnipeds, including the following families:

  • Phocidae (true seals)

  • Otariidae (eared seals and sea lions)

  • Odobenidae (walrus)

Sea otters are in family Mustelidae. Polar bears are in family Ursidae and are the only member considered to be a marine species. The order Sirenia includes manatees and dugongs.

Marine mammals have many adaptations to life in the aquatic environment, such as adaptations to high pressures, cold temperatures, low light conditions, and lengthy breath-hold diving. These adaptations may render veterinary examination and sampling more difficult compared to terrestrial animals, but these challenges can generally be overcome with experience and training. Few pharmaceuticals or vaccines are approved for use in marine mammals, although many recommendations exist based primarily on clinical experience in addition to published reports. Despite these reports, clinicians should be cautious in their application as effects are highly variable among species.

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