Marine Mammals

Interest in marine mammals has increased significantly in recent years, both in the general public and in the scientific and management communities. There is a growing awareness of the integral importance of marine mammals to healthy aquatic ecosystems, and of the growing threats that a variety of human activities pose to these animals and their environments. Research and education programs are seeking to better understand and more clearly communicate the nature of these threats and to recommend appropriate steps to reduce or eliminate their impacts.

Marine mammals generally include whales, dolphins, porpoises, seals, sea lions, walruses, manatees, dugongs, marine and sea otters, and polar bears. The term 'marine mammal' commonly refers to members of five different mammalian groups: cetaceans (whales, dolphins, and porpoises), sirenians (manatees and the dugong), pinnipeds (sea lions, the walrus, and seals), marine and sea otters, and the polar bear. These diverse groups are currently thought to represent five or six different recolonizations of the water by land-dwelling ancestors. The term marine mammal, therefore, implies no systematic or taxonomic relationship. In fact, the cetaceans are more closely related to horses, pigs, and zebras than they are to other marine mammals, the pinnipeds have more in common with bears and weasels, and the sirenians are more closely allied to elephants and hyraxes. These differences not withstanding, however, all marine mammals have one thing in common - they derive all (or most) of their food from marine (or sometimes fresh) water.

All marine mammals have undergone major adaptations, which permit them to live in the water. The cetaceans and sirenians spend their entire lives in the water, while other marine mammals come ashore for various reasons, at particular times in their life cycle (most commonly to reproduce, moult, or rest). Major structural modifications to the bodies of cetaceans, sirenians, and pinnipeds involve the loss of hind limbs (cetaceans and sirenians), the adaptation of limbs for propulsion through water (pinnipeds), and the general streamlining of the body for hydrodynamic efficiency (all three groups). Structural modifications to the marine and sea otters and the polar bear by a marine existence are less apparent in body form; these animals still closely resemble their terrestrial counterparts.

Information extracted from Jefferson, T.A., S. Leatherwood, and M.A. Webber. FAO species identification guide. Marine mammals of the world. Rome, FAO. 1993.320 p. 587 figs.