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While the majority of cetaceans live in marine environments, a small number reside solely in brackish water or fresh water. Having a cosmopolitan distribution , they can be found in some rivers and all of Earth's oceans, and many species inhabit vast ranges where they migrate with the changing of the seasons.
They propel themselves through the water with powerful up-and-down movement of their tail which ends in a paddle-like fluke, using their flipper-shaped forelimbs to maneuver. [4] While the majority of cetaceans live in marine environments, a small number reside solely in brackish water or fresh water.
While the majority of cetaceans live in marine environments, a small number reside solely in brackish water or fresh water. Having a cosmopolitan distribution , they can be found in some rivers and all of Earth's oceans, and many species inhabit vast ranges where they migrate with the changing of the seasons.
Some species of cetacean live in rivers and lakes, but are more closely related to oceanic dolphins or porpoises and entered fresh water more recently. Such species are considered facultative freshwater cetaceans as they can use both marine and freshwater environments.
Both cetaceans and sirenians are fully aquatic and therefore are obligate water dwellers. Pinnipeds are semiaquatic; they spend 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. [1]
Beaver dams restrict water flow, creating a pond. Beaver ponds have a profound effect on the surrounding ecosystem. Their first and foremost ecological function is as a reservoir for times of drought, and prevent drying of riverbeds. In the event of a flood, beaver ponds slow down water-flow which reduces erosion on the surrounding soil. [51]
The physiology of underwater diving is the physiological adaptations to diving of air-breathing vertebrates that have returned to the ocean from terrestrial lineages. They are a diverse group that include sea snakes, sea turtles, the marine iguana, saltwater crocodiles, penguins, pinnipeds, cetaceans, sea otters, manatees and dugongs.
However, cetaceans are often indirect victims of fishing, in at least two ways. The first is the phenomenon of "bycatch", whereby small cetaceans (particularly dolphins [56]) can become trapped in nets, where they have been attracted by the high concentration of fish and end up drowning. [57]