Common bottlenose dolphin

Natural history

Dolphins engage with their environment through sound. An apparent cacophony of clicks, squeaks and whistles helps individuals identify and communicate with one another. Pulses of sound emanating from a dolphin’s forehead enable it to locate and perhaps stun prey animals, which includes schooling fishes, such as anchovies, or crustaceans and other ocean invertebrates. Due to peglike teeth and weak chewing muscles, dolphins devour their prey whole; one bottlenose dolphin may consume 32 pounds (14.5 kg) of fish in a day.

Bottlenose dolphin society can be as fluid as their marine environment, with relationships among individuals repeatedly forming and fissioning. Populations in the eastern Pacific and North Atlantic also occur in two physically, genetically and behaviorally distinct coastal and offshore forms. These coastal and offshore populations do not overlap or interbreed and could become—or already be—separate species.

In Monterey Bay

Around 300 individuals may comprise California’s coastal bottlenose dolphin population, staying close to shore between San Francisco Bay and Cabo San Lucas, Mexico. Coastal dolphins can be spotted from beaches, bluffs or boats. Offshore this pod is infrequently seen as its members stay seaward of the continental shelf. Bottlenose dolphins move seasonally between the Southern California Bight and Monterey Bay, but they had been relatively rare around Monterey Bay before following warmer water and extending their range northward in the early 1980s.

Conservation

This species is classified as being of "Least Concern" by the International Union for Conservation of Nature (IUCN) given its abundance and widespread distribution.

Bottlenose dolphins are the most commonly housed cetacean for sea parks and other purposes of public display. This species is caught intentionally in harpoon and drive fisheries for human consumption or for use as shark bait. But incidental bycatch in bottom-set gillnets and purse-seine nets poses a bigger conservation concern.

Coastal-dwelling dolphins are exposed to toxic pollutants such as mercury and PCB and as carnivores tend to concentrate more toxins in their bodies. Very high levels of both PCB and a by-product of the banned pesticide DDT were detected in dolphins sampled from the California coast. Such toxins have been correlated with immune system damage and failure in calving.

Cool facts

• Bottlenose dolphins in Shark Bay, Australia learned to wear sponges over their beaks while foraging among sharp coral—the only known case of cetacean tool use.
• As is true for all cetaceans, a dolphin’s nostrils have shifted to the top of its head, becoming a blowhole that permits easy breathing at the water’s surface.
• A bottlenose dolphin contains three times more blood than a human by body weight, increasing the dolphin’s oxygen-storage capacity during dives.
• When asleep, a dolphin keeps half of its brain awake in order to keep breathing.