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Pacific White sided Dolphin

Pacific White-sided dolphins are one of the more acrobatic and social of the "lags", dolphins that have a short, blunt rostrum. They are found only in the waters of the northern Pacific Ocean, their range stretching up the California coast into British Columbia and also to Japan, staying in temperate waters. These dolphins are usually seen offshore, or along the edge of the continental shelf, though they may come closer to shore in deeper waters made by underwater canyons. The tip of their rostrum is black, and a grey patch comes back to make a circle around.Resembling the Dusky dolphin, though the two species never mix, the Pacific White-sided dolphin is characterized by the white underside of the body, with light grey along the sides, and a dark grey or black coloring on the top .Their eyes. Also, the front edge of their dorsal and pectoral fins are black or dark grey, with the trailing edge more often a paler grey shade, making them a very complex looking dolphin.Pods may range in groups of one hundred, though when feeding, these split up into smaller groups. Sights of several thousand are common but mostly occur offshore. When they get together, the disturbance in the water is plain to see from all their splashing.

Look For: A dolphin with a curved back. Has a black-and-white belly. Rides the bow waves of ships

Length: Body up to 8' long.

Habitat:These dolphins, as well as the order of Cetacea, were once land creatures. Throughout million years of evolution, the animals have adapted completely to the water (Brust 1990). Land has now become a barrier. Pelagic Pacific white-sided dolphins are restricted to the temperate Northern Pacific Ocean. They seem to like ocean bottoms with ridges and slopes, which are excellent areas for prey (Leatherwood and Reeves 1987). Although these dolphins are considered to be deepwater marine mammals, occasionally they can be found 100 miles away from the shore (Kreitman and Schramm 1995). Shifting northward and southward, or inshore and offshore, depends on water temperature change. Compared with large whales, these dolphins travel relatively short distances. They can also migrate hundreds of miles seasonally for prey availabilities (Leatherwood et. al 1988, Brust 1990).

Range: Alaska to southern California.

Socialization and Reproduction:The Pacific White-Sided Dolphin lives in coastal waters off the B.C. coast in the Northern Pacific. These lively animals are generally found in large herds, sometimes as big as several thousand individual animals. These herds are generally the largest in September and October, averaging about 115 individuals, whereas in the winter months the herds are usually only 35 members large (though this is still a large group). Herd size peaks in the fall because this time of year is breeding season for these animals. Once they reach a length of 1.8m (6 ft) Pacific White Dolphins begin reproducing and have a gestation period (pregnancy) of 10-12 months. At birth, these marine mammals are about 1m (3 ft) in length.

The Pacific white-sided dolphin is one of the most abundant cetaceans in the North Pacific. In the last few years, it has been sighted more frequently and in larger numbers in the inshore waters of British Columbia. Research becomes increasingly important as fish stocks dwindle, and the dolphins become a factor in the survival of some of the west coast salmon stocks.

Feeding and Predation:Lags are carnivorous and feed primarily on squid, herring, sardines, hake, and anchovies. Their primary cause of death at present is human activity; they often become entangled in fishing nets which prevents them from coming up for air. These animals also fall victim to killer whales, and the occasional shark.

Communication:Like all dolphins, Pacific White Sides use sonar (a series of rapid clicks) for communication and to locate objects, such as prey and obstacles. Dolphins are thought to be extremely intelligent, in fact some scientists say they are as intelligent as humans. However, measuring intelligence is not an easy task so this is a difficult comparison to make. In fact we often end up measuring how similar animals are to humans, rather than their absolute intelligence. The vocabulary of these animals is incredibly diverse and includes squeaks, squawks, groans, rattles and clicks. They are also able to mimic the sounds of other animals, and they can be trained to perform according to human vocal instruction.

Appearance and Behaviour

Pacific White-Sided Dolphins are usually 2.1m to 2.4m (7-8ft) and weigh 90 to 140 kg. These robust animals are mostly black with a gray and white dazzle pattern, short thick beaks, and curved dorsal fins. However, they can usually be recognized from a distance by there playful behaviour. White-sides (or lags as they are often called) are extremely acrobatic and social animals. They love to perform somersaults and cart wheels and even swim along on their backs. They truly appear to be awaiting applause! In fact, one lag even jumped onto the deck of a ship, which was 3m (10ft) above the water. This animal was quickly thrown back into the ocean by the amused crew! Pacific White Sided dolphins have been observed swimming and/or feeding in the company of many other marine mammals, including the Northern Right Whale and Risso's dolphin, just to name a few.

 

Description :A dark grey or black back broken by white or light grey stripe along the flank characterizes this dolphins colouring. The beak, front edge of dorsal fin, flippers and flukes are dark; the belly white.


Distribution: This creature inhabits the entire Pacific range. It is considered a deepwater species but in recent years they have been seen closer to shore and in inland waters.


Biology :This fast, powerful swimmer loves to bow ride and surf; they often leap and somersault. They are nearly always found in groups of less than 50 animals. Primary foodstuff is squid and small fish. This animal is considered common and not endangered; some are harvested for food by the Japanese and several thousand are caught in drift nets and the tuna fishery each year.

Living in the deep temperate waters of the North Pacific, this dolphin has a tall, hooked dorsal fin which is half white and a white belly. It weighs about 200 lbs. and grows to about 7 ft. in length. At times, it can be found as far south as Baja California and the Sea of Japan.

The Pacific white-sided dolphin was named by Thomas Nicholas Gill, a librarian of the Smithsonian Institution, in 1865. Based on three skulls collected in San Francisco ten years earlier, he classified this species Lagenorhynchus obliquidens. The genus name Lagenorhynchus is derived from the Greek lagenos, meaning "bottle", and rhynchus, meaning "snout", while the species name obliquidens comes from the Latin words obliquus (slanting) and dens (teeth) (May 1990, Würtz 1998).

Evolution:Dolphins were regarded as fish by Greek philosophers. Until 1758, when Linnaeus rectified this mistake, he classified them as mammals (Coffey 1977). Unlike fish, dolphins use lungs to breathe. They are warm-blooded, with a steady body temperature regardless of the surrounding temperature. Their calves are nurtured in mothers’ womb and fed with milk after birth (Brust 1990).
Dolphins, whales, and porpoises belong to the order of Cetacea which is comprised of three suborders: Archaeoceti (ancient whales), Mysticeti (baleen whales), and Odontoceti (toothed whales). Tracing the evolution of cetaceans, most scientists agree that cetaceans and ungulates (hoofed mammals), such as sheep, cows, and pigs, descend from the same ancestor. Evidence of this has been found by Boyden and Gemeroy at Rutgers University, New Jersey in 1950 (Würtz 1998). Later, Sarich and Lowenstein, researchers at University of California Berkeley and U.C. San Francisco respectively, studied proteins in blood serum and found a striking relationship between cetaceans and hippopotamus (Würtz 1998); however, DNA studies have not yet confirmed this discovery (Gulf of Marine Aquarium 1999).The origin of cetaceans traces back to the early Paleocene (65 million years ago) (Würtz 1998). It used to be believed that cetaceans evolved from insectivores (Coffey 1977, Leatherwood and Reeves 1987). Now, scientists believe that the order Cetacea and Artiodactyla, the progenitor of hoofed animals, shared a common ancestor-Condylarthra. The family Mesonychidae of Condylarthra order inhabited the riverfronts of Tethys Sea, which is today’s Mediterranean Sea and Persian Gulf. Their dentition indicated that this family included herbivores and carnivores. At the beginning, these terrestrial animals preyed on mollusks and slow-moving fish. As the growing population increased resource competition, their teeth developed to be capable of catching fast-swimming fish as well. Towards the end of Paleocene, the mesonychids gave rise to archaeocetes, the true cetaceans (Gakin 1982, Evans 1987, Würtz 1998).Fossils found in Pakistan indicate a link between mesonychids and archaeocetes. About 52 million years ago, Ambulocetus natans adapted to aquatic life and was able to move on dry land as well. It swam by paddling its webbed back feet and undulating its long tail. Its movement on dry land resembled seal and sea lions (Würtz 1998).

The Protocetidae is the earliest family of archaeocetes; they were not physiologically well adapted to the ocean. Paleontologists discovered some fossil remains of Pappocetus in Nigeria and Egypt in the 1960’s. Pappocetus was comparatively small (8 ft). The nostrils were still in the front, and the inner ears had not yet developed to adapt to live in water. But, their various teeth forms suggested different levels of adaptation to food in the water. Scientists believe that until the Eocene (50 million years ago), the protocetids had completely adapted to aquatic life based on the fossils of primitive Pakicetus found in Pakistan in 1980 (Würtz 1998).

During the Oligocene (38-25 million years ago), the Archaeoceti diversified into two suborders of the modern cetaceans: Odontoceti and Mysticeti. The body became more streamlined, and a dorsal fin had developed. Unlike the previous suborders, nostrils retreated further back along the head. By the late Oligocene, the teeth of odontocetes evolved into cone shapes and became homodont (Evans 1987).The Squalodelphidae, the primitive dolphins family, appeared in the early Miocene (23 million years ago). Fossil records suggested that they inhabited in Europe, North and South America, and the freshwater of Australia. Most of them were about three meters in length with long snouts and lots of homodont teeth (Evans 1987).

The family Delphinidae came in the late Miocene (11 million years ago). According to the fossils found mostly in Europe, scientists suggest that this is the most diverse cetacean family, which includes today's common dolphins, killer whales, and Pacific white-sided dolphins (Evans 1987).

Today, after 65 million years of monophyletic evolution, cetaceans have branched off into 9 families, 38 genera, and 76 species. Pelagic dolphins are distributed all over the ocean from the tropics to the temperate regions, while freshwater dolphins can be found in Gange, Indus, or Amazon river systems.

Controversy:Between 1960 and 1990, 4,600 porpoises, dolphins, and small whales were caught for research, military, or display purposes. The Pacific white-sided dolphin was the first dolphin to be drafted into the US Navy. In 1960, researchers at the Naval Ordnance Test Center at China Lake, California, obtained a dolphin from a park in Los Angeles and named her Notty. The US Navy was interested in Notty's streamlined body, and it hoped to find out some ideas to improve the torpedo design (May 1990). Training and working with the dolphins have continued since

Arguments about captivity are extreme. Some argue that it is inhumane while others argue that it is good for educational purposes; people get a chance to see the animals in person. That certainly brings more profits to marine parks and aquariums. However, 75 percent of the captive dolphins are females and most of them are immature, this affects the population in a long run (May 1990). Besides, they lost their abilities to hunt food. If they are released back to the ocean, they will be less likely to survive.

References:

Brust, Beth. 1990. Dolphins and Porpoises. Minnesota: Creative Education.

Connor, Richard. 1994. The Lives of Whales and Dolphins. New York: Henry Holt and Company.

Coffey, D.J. 1977. Dolphins, Whales and Porpoises. New York: Macmillan Publishing Co., Inc..

Carwardine, Mark. 1995. Whales, Dolphins, and Porpoises. New York: A Dorling Kindersley Book.

Evans, Peter. 1987. The Natural History of Whales & Dolphins. New York: Facts on File Publications.

Gaskin D.E.. 1982. The Ecology of Whales & Dolphins. New Hampshire: Heinemann.

Gulf of Marine Aquarium. 1999. [Online] Available:

Klinowska, Margaret. 1991. Dolphins, Porpoises and Whales of the World: The IUCN Red Data Book. United Kingdom: Cambridge.


Kreitman, Richard C., Mary Jane Schramm. 1995. West Coast Whale Watching: The Complete Guide to Observing Marine Mammals.

San Francisco: HarperCollinsWest.


Leatherwood, Stephen., Randall R. Reeves. 1983. The Sierra Club Handbook of Whales and Dolphins. San Francisco: Sierra Club Books.


. 1987. The Sea World Book of Dolphins. San Diego: Harcourt Brace Jovanovich.


et. al 1988. Whales, Dolphins, and Porpoises of the Eastern North Pacific and Adjacent Artic Waters.

New York: Dover Publication.

May, John. 1990. The Greenpeace Book of Dolphins. New York: Sterling Publishing Company, Inc..

National Marine Mammal Laboratory. [Online] 9 Oct. 2001.


Pacific White sided gallery