Dolphin

The dolphin is a marine mammal belonging to the large order of cetaceans, which also includes whales and porpoises. Most dolphin species belong to the family Delphinidae and inhabit the ocean, though some species live in rivers such as the Amazon and Ganges.

Dolphins are air-breathing animals whose reproduction is live-bearing; they give birth to calves and nurse them with milk. They are therefore not fish, despite their fish-like form. They inhabit both cold and warm seas throughout the world.

Body and anatomy

The body is streamlined and smooth to move easily through water. They have front fins that evolved from limbs (flippers), a rear fin usually pointing upward, and a fluked tail that moves up and down. The blowhole, located on the head, is where they breathe when surfacing. Size varies: some species are less than two meters long, while orcas can reach several meters.

Echolocation and sound

Dolphins use echolocation: they emit clicking sounds and listen to the echoes returning from them to sense location, size, and movement of nearby objects. This enables them to navigate in murky water. They also use whistles and various other sounds to communicate within their pod; some species have individual whistles used for recognition.

Social behavior

Dolphins live in groups called pods, varying in size from several individuals to over a hundred. Cooperative hunting behavior directed at fish has been documented, as have learned behaviors passed between pod members. Diet consists mostly of fish and squid; orcas also hunt other marine mammals.

Threats and conservation

Major threats include incidental capture in fishing nets (bycatch), water pollution, underwater noise that disrupts echolocation, and habitat change. River-dwelling species are particularly vulnerable, since dam construction and pollution restrict their ranges. Threat levels vary by species.