MERR Institute, Inc. 801 Pilottown Road | Lewes, DE 19958 | (302) 228-5029 | Email

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DOLPHIN SPECIES

The Delaware Coastline is home to several species of dolphins, a favorite marine mammal of beachgoers who watch them swim and play off the shoreline. Every year, MERR Institute participates in a Dolphin Count to help monitor local populations.

 
Striped
Dolphin

(Stenella coeruleoalba)

Anatomy:

  • Appearance: Black patch around each eye, thin dark streak behind eye. One or two dark bands between eye and flipper, dark beak and flippers. Pale gray finger-shaped marking below dorsal fin, bluish gray or brownish upper side. Pale gray tail stock, white or pink underside, pale gray sides. Thin, dark stripe running from underside of tail stock to eye

  • Birth size: 22lbs. 39 in.   

  • Adult size: 200-330 lbs. 6-8¼ ft.

  • Dorsal fin: Position in center, dark, strongly falcate, some fins exceptionally tall in relation to body size, trailing edge may be highly concave.

Behavior:

  • Active and highly conspicuous, frequently breaches, sometimes as high as 23 ft. Capable of amazing acrobatics, including back somersaults, tail-spins, and upside down porpoising.

  • When swimming at speed, up to one-third of all members of the pod will be above the surface at any one time.

  • Dives last 5-10 min, will bow-ride in some areas, but rarely approaches vessels in some areas.

  • Smaller groups tend to occur in the Atlantic and Mediterranean; often associates with common dolphins and yellowfin tuna.

  • When feeding, dives to at least 655ft deep.

  • Several mass strandings have occurred in recent years.

Fun Facts:

  • Stripped Dolphins have not been successfully kept in captivity

  • Striped dolphins are conscious breathers, meaning they never fall completely asleep and are always partially aware of their surrounding; even when at rest. This allows these marine mammals to come up for air when necessary and maintain awareness of potential threats.

  • It has been estimated that over 20,000 striped dolphins may have been killed during the 20th century to be used for food and/or raw materials.

Group size:

  • 10-500

Location:

  • Inshore and Offshore

Status:

  • Common

Distribution:

  • Warm temperate, subtropical, and tropical waters around the world.

Threats:

  • Entanglement in fishing nets

  • Hunting/whaling

Prey:

  • Fish, squid, and shrimp

 
 
Atlantic Bottlenose Dolphin

(Tursiops truncates)

Anatomy:

  • Appearance: Subdued gray coloring, dark bluish gray or brownish gray dorsal cape. Off-white, light gray, or pinkish underside. Paler gray or brownish gray sides, may be extensive scarring on some adults.

  • Birth size: 35-65 lbs. 34in-4 ½ ft.   

  • Adult size: 330-1,435 lbs. 6 ¼- 12 ¾ft

  • Dorsal fin: Central position, prominent, falcate.

Behavior:

  • Highly active at the surface: frequently lobtails, bow-rides, wake-rides, body-surfs, rides pressure waves of large whales, and breaches.

  • Powerful swimmers, dives rarely last longer than 3-4 minutes inshore but longer offshore. Shows forehead when surfacing, but rarely the beak, will chase fish out of the water, beaching itself and then wriggling back.

  • May be found in association with a variety of other cetaceans, sharks, and sea turtles.

  • Non-migratory

Fun Facts:

  • Wild Bottlenose Dolphins have been observed using tools! They will place marine sponge on their beaks to protect them when searching for food on the sandy sea bottom.

  • They have saved humans before! Occasionally bringing injured divers to the surface!

Group size:

  • Inshore: 1-10

  • Offshore: 1-25 though can be found in pods up to 500 in size

Location:

  • Inshore and Offshore

Status:

  • Common

Distribution:

  • Widely distributed in cold temperate to tropical seas worldwide

Threats:

  • Entanglement in fishing nets 

  • Pollution, habitat destruction, and human disturbance

  • Hunting/whaling 

Prey:

  • Fish, squid, and shrimp

Atlantic white-sided Dolphin

(Lagenorhynchus acutus)

Anatomy:

  • Appearance: Dark ring around eye, black or dark gray upper side. Yellow or tan band along each side of tail stock, white underside. White band below dorsal fin, pale gray stripe along length of body, black or dark gray dorsal fin.

  • Birth Size: 65-75lbs. 39in-4¼ ft.  

  • Adult Size: 365-440lbs. 6¼- 8¼ ft.

  • Dorsal fin: Position is slightly forward of center, tall, falcate (more erect in adult males), black or dark gray in color.

Behavior:

  • Acrobatic and fast swimmer; frequently breaches and lobtails. Surfaces to breathe every 10-15 seconds (leaping clear of water or barely breaking the surface creating a wave over its head). Will swim alongside of slower vessels and may bow-ride in front of fast vessels, sometimes rides bow waves of large whales.

  • Found in large schools offshore and smaller schools inshore.

  • Individual and mass strandings are relatively common

Fun Facts:

  • Very social animals, often hangs out with other sea animals such as humpback whales, fin whales, and white beaked dolphins.

  • Complex social groups, pods are often divided by age and sex.

Group size:

  • 5-50, though pods of up to 1,000 recorded offshore

Location:

  • Inshore and Offshore

Status:

  • Common

Distribution:

  • Cool temperate and sub-arctic waters of the North Atlantic

Threats:

  • Entanglement in fishing nets 

  • Hunting/whaling 

Prey:

  • Fish, squid, and shrimp

 
 
Common Dolphin

(Delphinus delphis)

Anatomy:

  • Appearance: Criss-cross or hourglass pattern on sides. Gray, black, purplish black, or brownish cape, with V shape under dorsal fin. Tan or yellowish patch on both sides. 1 or 2 broken yellow or gray lines interrupt white underside. Complex coloration on head, gray or black beak may be white-tipped. Pale gray tail stock, white or creamy white underside. Black or gray flippers, dark streak from flipper to middle of lower jaw

  • Birth Size: 32-35 in.  

  • Adult Size: 155-245 lbs. 5¾ - 8 ft.

  • Dorsal fin: Position in center, ranges from strongly falcate to nearly triangular. Color can range from black to mostly grayish white, gray or black border, pale gray center. Concave trailing edge.

Behavior:

  • Frequently porpoises, slaps water with chin, lobtails, flipper-slaps, bow-rides, and breaches.

  • Dives can last up to 8 min, but usually 10 seconds to 2 min.

  • Often found in large, active schools, several members of the group often surface together. School size often varies seasonally and according to time of day. Animals bunch together when frightened.

  • Highly vocal: high pitched squealing can be heard above the surface

Fun Facts:

  • The Common Dolphin can vary so much in appearance that over 20 different subspecies have been proposed over the years.

  • One of the most abundant cetaceans, with a population estimated to be in the millions!

Group size:

  • 10-500

Location:

  • Inshore and Offshore

Status:

  • Common

Distribution:

  • Warm temperate, subtropical, and tropical waters around the world

Threats:

  • Entanglement in fishing nets 

  • Pollution and human disturbance

  • Hunting/whaling 

Prey:

  • Fish and squid

 
Rissos' Dolphin

(Grampus griseus)

Anatomy:

  • Appearance: Body covered in white scars, crease down the center of the forehead. Pale underside with a blue-gray, gray-brown, or almost white body color. Gray at birth but color fades with age

  • Birth Size: 4¼-5¾ ft.   

  • Adult Size: 660-1100 lbs. 8 ½ -12 ½ ft.

  • Dorsal fin: very tall (up to 20in high), tip may be rounded or pointed with concave trailing edge. Position is central.

Behavior:

  • Young are known to breach, older animals tend to do a half breach, then slap side of head onto the surface.

  • Spyhops high in the water with flippers exposed, may lobtail and flipper-slap, and will surf in waves. Seldom bow-rides but may swim alongside a vessel or in its wake.

  • Dives for 1-2 min, then takes up to a dozen breaths at 15-20 second intervals, can stay underwater for up to 30 min. Flukes may appear above water when diving, sometimes swims by porpoising, may surface at 45 degree angle to breathe.

  • Groups spread out in a long line when hunting.

  • Sometimes seen in mixed schools with several species of dolphins and pilot whales.

Fun Facts:

  • Also known as the Monk Dolphin

  • These guys are fighters! Almost all Rissos’ Dolphins are covered in scars by the time they reach adulthood.

  • The only species of dolphin in the genus Grampus

Group size:

  • 3-50, though temporary gatherings of several hundred

Location:

  • Inshore and Offshore

Status:

  • Common

Distribution:

  • Deep tropical and warm temperature waters in the northern and southern hemispheres

Threats:

  • Entanglement in fishing nets 

  • Hunting/whaling 

Prey:

  • Fish and squid

Atlantic Spotted Dolphin

(Stenella frontalis)

Anatomy:

  • Appearance: Can be identified by spotting in older animals, dark purplish gray cape on upper side. Tall, falcate dorsal fin with pointed tip, usually unspotted. Light spots cover dark areas of body and dark spots cover light areas of body. White underside, a long, chunky beak tipped with white. Curved, pointed and unspotted flippers with a light gray band between eye and flipper

  • Birth Size: 32in- 4 ft.  

  • Adult Size: 220-310lbs. 5 ½ -7 ½ ft.

  • Dorsal fin: tall, falcate dorsal fin; centrally positioned; some curve distinctively backward with a strong concave trailing edge; usually unspotted; pointed tip

Behavior:

  • Very active at the surface, breaches, hurling itself high in the air. Most aerial behavior observed during feeding.

  • Fast and energetic swimmer

  • Long, shallow leaps, bow rider, tip of beak surfaces first followed by head, back and dorsal fin

  • Fairly complex social structure, individual recognition and bonding is common in social structure

Fun Facts:

  • These dolphins are not shy at all. They are known to swim right up to humans in the Bahamas and try to play with them!

Group size:

  • 5-15 though may gather in groups of a few hundred temporarily

Location:

  • Inshore and Offshore

Status:

  • Common

Distribution:

  • Warm temperate, subtropical, and tropical waters in both the North and South Atlantic

Threats:

  • Entanglement in fishing nets 

  • Hunting/whaling 

Prey:

  • Fish, squid, and other inverts

Rough Toothed Dolphin

(Steno bredanensis)

Anatomy:

  • Appearance: Long, narrow beak with white “lips” and throat. Conical head, smoothly sloping forehead without crease between beak and forehead. Dark gray of bluish gray cape, a robust body in front of dorsal fin. Large, pointed flippers and a white or pinkish white underside. Pinkish or yellowish white blotches or spots on lower half of body. Its body is slimmer behind dorsal fin, broad flukes, some may be heavily scarred.

  • Birth Size: 39 in. 

  • Adult Size: 220-330 lbs. 7- 8½ ft.

  • Dorsal fin: Pointed tip, trailing edge always concave, wide base. Leading edge usually at 45 degree angle to body, fin may be highly falcate.

Behavior:

  • Rarely does more than a half-hearted breach, a fast swimmer.

  • Porpoising with low arc-shaped leaps, bow-rides in front of fast-moving vessels, may be seen logging

Fun Facts:

  • The rough-toothed dolphin can be found in all three major oceans of the world (the Atlantic, Pacific and Indian).

  • While the rough-toothed dolphin is a social species, some are “lone-wolves” who tend to travel without a pod.

Group size:

  • 10-20 though sometimes in groups of several hundred

Location:

  • Offshore

Status:

  • Unknown

Distribution:

  • Warm temperate, subtropical, and deep tropical waters around the world

Threats:

  • Entanglement in fishing nets 

  • Hunting/whaling 

Prey:

  • Fish and squid

HARBOR PORPOISE
(Phocoena phocoena)

Anatomy:

  • Appearance: Black lips and chin, straight mouth line angled slightly upward. 1-3 stripes from jawline to flippers. Small, dark, rounded flippers located in white body area. A white underside with a black or dark gray back. Flukes dark on both sides, body color merges from dark to light through freckling.

  • Birth Size: 11 lbs. 26-36 in  

  • Adult Size: 125-145 lbs. 4 ¾ -6 ¼ ft.

  • Dorsal fin: Blunt tip, concave trailing edge, and a broad base. Black or dark gray in color, longer leading edge may have small bumps

Behavior:

  • Makes arc shaped leaps when chasing prey

  • Surfaces up to 8 times at 1 minute intervals when traveling, and long periods of inactivity when resting at the surface.

  • Rolls to reveal flashes of white

  • Blow not seen often, but it is heard

Fun Facts:

  • Harbor Porpoises are one of the smallest marine mammals.

  • In Medieval times, Harbor Porpoises were known as “Pig-Fish”

Group size:

  • 2-5

Location:

  • Inshore 

Status:

  • Common

Distribution:

  • Cool temperate and sub-arctic waters of the northern hemisphere

Threats:

  • Entanglement in fishing nets

  • Pollution and habitat destruction

  • Hunting/whaling

  • Human disturbance

Prey:

  • Fish, squid, and shrimp