Bottlenose dolphin

Page - September 21, 2007

Estimated population:

The exact worldwide population of the bottlenose dolphin is not known. In the eastern tropical Pacific the population is estimated to be 243,500, while in the waters of Japan the population estimates are as low as 37,000.

Ways to identify this species:

Bottlenose dolphins are gray with a soft color pattern, have a robust body with a short to medium-length beak, and a large curved dorsal fin. This species usually travels in groups of 10-25 and are often seen very close to shore. They can travel in groups of hundreds when off-shore.

Biology

  • Dolphins are considered to be some of the most intelligent species on Earth.
  • Bottlenose dolphins measure from 8-12 feet and typically weigh between 400 and 600 pounds.
  • This species feeds on a variety of organisms depending on habitat location. They eat invertebrates, pelagic and mesopelagic fish, and are often attracted to trawlers where they feed on escaped fish.
  • They use echolocation-bouncing sound off objects to determine their location-to hunt and use a series of high-pitched clicks to stun prey.
  • Dolphins have strong eye muscles that can change the shape of the eye lens in order to focus in both air and water.
  • Females usually give birth every 3 years, with gestation lasting a year.
  • The average life span of a male dolphin is between 40 and 45 years, while females tend to at least 5 years longer.
  • Bottlenose dolphins like to surf in breakers and waves from whales or storms, and are well-known for riding the bow waves of powered vessels.
  • Bottlenose dolphins often associate with other cetacean species such as pilot whales; however, they may become aggressive if other species try to occupy their bow-riding territory.

Threats

  • This species has two major natural predators; killer whales and sharks.
  • Climate change has affected certain populations of this species. The California coastal population has been pushed northward due to rising water temperatures associated with El Niño events.
  • Bottlenose dolphins often get caught in fishing nets and are adversely affected by pollution and near shore habitat destruction.
  • Bycatch in tuna nets has been a significant contribution to dolphin mortality. In 1990, a program to label tuna cans "Dolphin safe or Dolphin friendly" drastically reduced the number of tuna-related deaths. Standards have since been weakened and dolphins remain at risk.

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