|Short-beaked Common Dolphin Profile ||Fast Facts |
Two species of common dolphin play an important role in the Southern California Bight (SCB) ecosystem: Delphinus delphis, the short-beaked common dolphin, and D. capensis, the long-beaked common dolphin (Heyning and Perrin 1994). There are external differences between the two species in body length, beak length, coloration and shape of the melon. Furthermore genetic analyses (Rosel et al. 1994) have confirmed reproductive isolation between short-beaked and long-beaked common dolphins.
Short-beaked common dolphins have a gray body with a distinct criss-cross color pattern on the sides. These markings are crisp, and the yellowish patch is more intensely colored than in Delphinus capensis. In short-beaked common dolphins, the dorsal fin may be triangular or moderately falcate (curved); the dorsal fin and flippers may be all white or have white centers.
They are the most numerous dolphins in offshore warm-temperate waters of the Pacific Ocean. They live in large groups including hundreds of animals, sometimes forming superschools of 1000 dolphins or more.
Why study them now? Together, these two species are the most abundant cetaceans and the top cetacean predators in the SCB (Barlow et al. 2008). While responses to short- and long-term changes in climatic and oceanographic conditions can be expected, a large and growing coastal urban population in Southern California impacts the SCB and potential risks are emerging as threats to these populations. The risks include exposure to a wide range of anthropogenic impacts: commercial and recreational fisheries; habitat degradation due to pollution; effects of ship operations (e.g. noise and pollution) associated with two of the busiest commercial ports in the country (Los Angeles and Long Beach); and impacts associated with the U.S. Navy’s operations on the SCB test range. Evidence of exposure to some of these risks has been observed in specimens of stranded Delphinus species, especially D. capensis, which show vulnerability to domoic acid and effects of human interactions.
Scientific name: Delphinus delphis
Diet: Mesopelagic fishes & squids; epipelagic schooling species (small scombroids, clupeoids, market squids.)
Size: Males 5.6 to 6.6 ft (1.7 to 2 m)
Females 5.4 to 6.3 ft (1.6 to 1.9 m)
(Heyning and Perrin, 1994)
Life History: Preliminary data suggest that gestation lasts ~11 months. Males reach sexual maturity at ~10.5 years; females reach it at ~8.5 years (Ferrero & Walker, 1995)
Threats: Tuna purse-seine fisheries; gill nets.
IUCN Status: Lower Risk/Least Concern
Published research on D. delphis from SWFSC scientists:
Chivers, S. J., R. G. LeDuc, and K. M. Robertson. 2003. A feasibility study to evaluate using molecular genetic data to study population structure of eastern North Pacific Delphinus delphis. NOAA, NMFS, Southwest Fisheries Science Center Administrative Report LJ-03-12. 14pp.
Heyning, J. E., and W. F. Perrin 1994. Evidence for two species of common dolphins (genus Delphinus) from the eastern North Pacific. Natural History Museum of Los Angeles County Contributions in Science 442:1-35.
Jefferson, T. A. and Van Waerebeek, K. 2002. The taxonomic status of the nominal dolphin species Delphinus tropicalis van Bree, 1971. Marine Mammal Science 18:787-818.
Rosel, P. E., A. E. Dizon, and J. E. Heyning. 1994. Genetic analysis of sympatric morphotypes of common dolphins (genus Delphinus). Marine Biology 119:159-167.