Offshore Cetacean Species
Aside from the commonly seen cetacean species that we encounter on Stellwagen Bank, Jeffrey’s Ledge and the Great South Channel, there are several other species that CORE studies during our offshore research excursions. These species include common dolphins, striped dolphins, Risso’s dolphins, bottlenose dolphins, and sperm whales. While these species are generally observed at least 60 miles or further from the coast, some individuals have been observed as close as 5 miles from land, presumably following prey that has migrated towards shore.
Common Dolphins
(Delphinus delphis)
Physical Statistics: Also called the saddleback dolphin, the common dolphin is a medium-sized dolphin species, ranging 6-8 feet in length and weighing 300-350 pounds.
Field Marks: The common dolphin has a long, pointed snout, with a black stripe that runs from the lower jaw to the flipper. The dorsal fin is large and prominent. The most distinctive field mark is a sideways hour glass pattern that can be seen on each side of the body. The side forward of the dorsal fin is tan in color while the side aft of the fin is gray.
Habitat: Common dolphins are usually found over the edge of the continental shelf, feeding on a variety of fish and squid.
Interesting Fact: Common dolphins are one of the three major dolphin species (also including spinner and spotted dolphins) that associate with yellowfin tuna and thus are occasionally caught in purse seine nets by tuna fishermen. Over two million dolphins have died since the tuna fishery began!
Striped Dolphins
(Stenella coeruleoalba)
Physical Statistics: The striped dolphin is a medium-sized dolphin species, ranging 6-8 feet in length and weighing approximately 290 pounds.
Field Marks: Like the common dolphin, the striped dolphin has a long, slender snout and a very prominent dorsal fin. A pale blaze originating from the eye can be seen sweeping up toward the dorsal fin. The most noticeable field marks are two stripes that originate from the eye. The first stripe terminates at the flipper. The second, more noticeable stripe runs along the flank, terminating at the anus.
Habitat: Striped dolphins are usually found from the continental slope waters to the Gulf Stream, feeding on a variety of fish, shrimp and squid.
Interesting Fact: Ironically, most of the biological facts about striped dolphin have been obtained from fishermen in Japan, which have hunted this species for food for centuries!
Risso’s Dolphins
(Grampus griseus)
Physical Statistics: Also called grampus, the Risso’s dolphin is a large dolphin species, ranging 9-13 feet in length and weighing 650-1100 pounds.
Field Marks: The Risso’s dolphin has a large, bulbous forehead with a blunt snout. The dorsal fin is large and prominent, often appearing darker than the rest of the body. The most noticeable markings are the white scars and scratches that cover the back and sides of the body. At times, these scars are so numerous that the head and body appear all white, while the flippers and tail are darker.
Habitat: Risso’s dolphins are commonly found along the edge of the continental shelf feeding predominantly on squid.
Interesting Fact: The body color of a Risso’s dolphin changes three times during its life. At birth, the dolphin calf is gray. During its juvenile years, it is a dark brown color. As the individual ages, the scars presumably incurred during interspecies fighting or from the beaks and suckers of the squid it consumes eventually become so numerous that the body becomes white!
Bottlenose Dolphins
(Tursiops truncatus)
Physical Statistics: The bottlenose dolphin is a large dolphin species, ranging 8-12 feet in length and weighing 450-600 pounds.
Field Marks: The bottlenose dolphin is probably the species of dolphin that the public is most familiar with, exhibited in many aquariums worldwide. It has a short, thick beak and a large, prominent dorsal fin. The coloration of the body varies, being charcoal, bluish-gray or brown above and lighter below. A light wash may be seen extending up from the flipper to the dorsal fin.
Habitat: There seem to be two populations of bottlenose dolphins. The coastal population can be found from North Carolina south and west to the Gulf of Mexico feeding on a variety of fish and invertebrate species. The offshore population can be found along the continental shelf, feeding on fish and squid.
Interesting Fact: While in captivity, a bottlenose dolphin proved that intraspecies mating between dolphins is possible, producing a calf with a captive Risso’s dolphin!
Sperm Whales
(Physeter macrocephalus)
Physical Statistics: The sperm whale is the largest of the toothed whales, reaching 35-55 feet in length and weighing up to 45 tons.
Field Marks: The 15-foot spout of a sperm whale is tipped forward and to the left at approximately 45� due to the single blowhole located on the left side of the head. The sperm whale really does not have a dorsal fin, but a dorsal hump can be seen 2/3 of the way back from the tip of the head. The flippers are small and paddle-shaped. Upon diving, the sperm whale will arch its back showing the series of bumps called crenulations that run from the dorsal hump to the tail. The tail is large and triangular with a deep central notch. The dive may last from 20 minutes to over an hour. The sperm whale can be found singly or in pods.
Habitat: Sperm whales can be found along the edge of the continental shelf and further offshore, feeding on cephalopods and a variety of fish.
Interesting Fact: Although the albino sperm whale in the story of Moby Dick was fictional, actual albino sperm whales have been observed in the wild!
