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[4] 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.
Porpoises range in size from the vaquita, at 1.4 metres (4 feet 7 inches) in length and 54 kilograms (119 pounds) in weight, to the Dall's porpoise, at 2.3 m (7 ft 7 in) and 220 kg (490 lb). Several species exhibit sexual dimorphism in that the females are larger than males. They have streamlined bodies and two limbs that are modified into ...
In 2020, some 86 cetacean species were known worldwide, a number of which are endemic to freshwater or polar waters. [10] These highly charismatic mammals are reputed to have remarkable intelligence, which contributes to their popular success and hence to the desire to protect them. [11]
In the wild, females who survive infancy live 46 years on average, and up to 70–80 years in rare cases. Wild males who survive infancy live 31 years on average, and up to 50–60 years. [ 149 ] Captivity usually bears little resemblance to wild habitat, and captive whales' social groups are foreign to those found in the wild.
Cetaceans are famous for their high intelligence, complex social behaviour, and the enormous size of some of the group's members. For example, the blue whale reaches a maximum confirmed length of 29.9 meters (98 feet) and a weight of 173 tonnes (190 short tons), making it the largest animal ever known to have existed.
These delightful little angelfish are highly prized as aquarium fish, with an exorbitant price tag beyond the realms of most aquarists. A single fish has sold for $30,000.
River dolphins are relatively small compared to other dolphins, having evolved to survive in warm, shallow water and strong river currents. They range in size from the 5-foot (1.5 m) long South Asian river dolphin to the 8-foot (2.4 m) and 220-pound (100 kg) Amazon river dolphin.
Between 40% and 50% of their body weight is fat, which is a higher proportion than for cetaceans that do not inhabit the Arctic, where fat only represents 30% of body weight. [ 39 ] [ 40 ] The fat forms a layer that covers all of the body except the head, and it can be up to 15 cm (5.9 in) thick.