By far the largest family of dolphins and porpoises, oceanic dolphins encompass more than two dozen species. Most oceanic dolphins spend their lives ranging over vast areas of the open sea, far from land. Many species are distributed throughout the world ocean. Others, like the porpoises, are mainly coastal. A few species occasionally swim up rivers, and some even live there permanently, side by side with true river dolphins.

Oceanic dolphins, typically larger than river dolphins or porpoises, vary a great deal in size. The tucuxi - smaller than most porpoises - is only 1.4 to 1.8 m long and weighs 36 to 45 kg. The largest is the orca, or killer whale, which measures up to 9.8 m and can weigh 5,000 kg, making it even bigger than certain whale species, such as beaked whales. the oceanic dolphins include six large dolphin species that have the word "whale" in their common name. Because of their size, they are sometimes treated as whales for management purposes.

The threats affecting oceanic dolphins vary by species. Those in coastal waters suffer many of the same problems that porpoises do: shore pollution, ship traffic and fishing nets. Open-ocean dolphins encounter less pollution, but some, such as spotted and spinner dolphins, face another hazard: because many travel with tuna, they are often ensnared in tuna nets, where they drown. Even more extensive and deadly are the dee-sea drift nets which trap and kill almost everything that swims into them. Until such nets are banned, many species of dolphins, as well as fish and other marine life, are at risk.

We do not really know the status of most oceanic dolphins. Many species are probably less endangered than river dolphins and porpoises, whose ranges are far more restricted. And even if a number of oceanic dolphin populations are threatened, groups of the same species in other areas may remain healthy.

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