Short-beaked Common Dolphin

Description

The short-beaked common dolphin is one of the most beautifully marked and abundant cetaceans in the world’s temperate oceans. Adults measure 5.5 to 8.5 feet in length and weigh between 150 and 440 pounds. Their most distinctive feature is a striking hourglass color pattern on the flanks: a yellow or tan patch on the anterior (forward) side that transitions to a gray patch on the posterior (rear) side, creating a characteristic criss-cross pattern below the dorsal fin. The back is dark gray to black, and the belly is white. A dark stripe runs from the lower jaw to the flipper, and a dark circle surrounds the eye with a dark line extending forward to the beak. The beak is moderately long and slender, and the dorsal fin is tall and triangular to slightly falcate. Common dolphins have 40 to 55 small, sharp teeth in each row of both the upper and lower jaws, giving them a total of 160 to 220 teeth, more than most other dolphin species. They are sleek and built for speed, with a streamlined body shape.

Habitat & Range

Short-beaked common dolphins are found in temperate and warm-temperate waters of the Atlantic and Pacific Oceans, as well as the Mediterranean Sea. In the eastern North Pacific, they range from British Columbia to central Mexico, with the Southern California Bight representing a core area of abundance. They are by far the most abundant cetacean species encountered in the waters off Orange County, with the California Current stock estimated at over 400,000 individuals. Common dolphins prefer waters with sea surface temperatures between 50 and 82 degrees Fahrenheit and are typically found over the continental shelf and in offshore areas where productive upwelling zones concentrate their prey. They are commonly observed from whale-watch boats departing from Dana Point, Newport Beach, and other Orange County harbors throughout the year, with peak sighting frequency often occurring during summer and fall when warm, productive waters support abundant prey. Their distribution can shift significantly in response to oceanographic conditions such as El Nino and La Nina events.

Diet

Short-beaked common dolphins feed primarily on small schooling fish and squid. In the waters off Southern California, their diet consists largely of anchovies, sardines, Pacific saury, market squid, and lanternfish. They are highly active and energetic feeders that employ cooperative hunting strategies to corral and concentrate prey. Groups of dolphins work together to herd fish into tight, dense bait balls near the surface, then take turns dashing through the aggregation to feed. This behavior often attracts seabirds, sea lions, and even larger whales to the feeding area, creating spectacular multi-species feeding events that are a highlight of whale-watch trips off Orange County. Common dolphins feed both during the day and at night, and they are known to follow the deep scattering layer (a dense layer of organisms that migrates vertically in the water column) toward the surface at dusk to exploit prey as it rises. An adult common dolphin consumes approximately 10 to 20 pounds of food per day.

Behavior

Short-beaked common dolphins are among the most gregarious of all cetaceans, frequently forming groups of hundreds or even thousands of individuals. Mega-pods or super-groups of 10,000 or more dolphins have been documented in the waters off Southern California, creating a spectacle of leaping, splashing animals stretching to the horizon. They are fast swimmers capable of sustained speeds of 25 miles per hour and bursts exceeding 30 miles per hour, and they frequently engage in aerial behaviors including porpoising (leaping clear of the water in a series of arcing jumps), bow-riding alongside boats and ships, and wake-riding. Common dolphins are highly vocal, producing a wide variety of whistles, clicks, and burst-pulse sounds for communication and echolocation. They are known for their energetic and acrobatic nature, often leaping, spinning, and belly-flopping at the surface. Females give birth to a single calf after a gestation period of approximately 10 to 11 months. Calves are weaned at about 6 months of age but may remain with the mother for up to two years. The average lifespan is estimated at 25 to 35 years.

Conservation Status

The short-beaked common dolphin is listed as Least Concern on the IUCN Red List, and the eastern North Pacific population is considered healthy and abundant. In the United States, they are protected under the Marine Mammal Protection Act. Despite their overall abundance, common dolphins face several threats. Historically, they suffered significant bycatch mortality in the eastern tropical Pacific tuna purse-seine fishery, where dolphins and yellowfin tuna often school together. Reforms to the fishery, including dolphin-safe fishing practices, have dramatically reduced this bycatch. In California waters, drift gillnet fisheries have been a source of bycatch mortality, leading to regulatory efforts to reduce interactions. Other threats include ocean pollution, particularly the bioaccumulation of persistent organic pollutants such as DDT and PCBs (which are present at elevated levels in Southern California waters due to historical dumping), marine debris ingestion, and underwater noise pollution. Climate change and its effects on oceanographic conditions may alter the distribution and abundance of prey species upon which common dolphins depend, potentially shifting their range and affecting population dynamics.