INFORMATION AND CHARACTERISTICS.

The Northern right whale dolphin and its close relative the southern right whale dolphin (Lissodelphis peronii), are the only dolphin species of the family Lissodelphis that lack a dorsal fin. The naturalist Titian Peale was the first to describe this species in 1848. Its scientific name comes from word Lissos that means “soft” in Greek, and the Latin borealis which means “north.”

HOW DO THEY LOOK? PHYSICAL CHARACTERISTICS.

Morphology.
The slender, hydrodynamic body of the northern right whale dolphin allows it to reach great speed when swimming. Both species of the genus Lissodelphis are the thinnest of all the small cetaceans, and this, in particular, is endowed with a short “snout” and a tilted forehead, both separated by a fold. It has no dorsal fin but has two small, curved and pointed pectoral flippers.

Order: Cetacea
Family: Delphinidae
Genus: Lissodelphis

Weight and size.
Usually, males are larger and heavier than females. An adult male individual measures approximately 3.1 meters in length but the range of the female is 2.3-2.6 meters. The weight oscillates between 60 and 100 kilograms.

Skin Coloration.
The shining dolphin’s skin has a dark color on the dorsal area that contrasts with the white belly, however, this is little visible. Under the lower jaw, it has a white spot. Both the pectoral flippers and the caudal fin are black.

Distinctive characteristics.
It is easy to distinguish this dolphin from other species, but it can be confused with sea lions because of the lack of dorsal fin. It is necessary to observe the dorsum and the coloring pattern characterized by black and white to avoid confusion with other animals.

WHERE DO THEY LIVE? DISTRIBUTION AND HABITAT.

The Northern right whale dolphin has a limited distribution. It is found only in temperate and cold waters of the North Pacific Ocean between latitudes 30° and 50° north. They inhabit from northern Baja California in Mexico to the Gulf of Alaska, and in the west from Kamchatka in Russia to Japan. It is present in Russia, Mexico, the United States, Canada, and Japan.

It inhabits waters of the platform and the continental slope of great depth as well as (occasionally) areas near the coasts as long as they are deep. The temperature of its habitat is generally below 19° C but can tolerate those equal to or less than 24° C.

WHAT DO THEY EAT? DIET AND EATING HABITS.

Fish and cephalopods make up most of the diet of this carnivorous dolphin. It feeds on a wide variety of species. Some of its favorite prey are:

– Lanternfish (myctophids).
– Hake.
– Saury (family Scomberesocidae).
– Octopus.
– Squid.

When they inhabit around the center of the Pacific Ocean, the lanternfish make up the prey most consumed by this dolphin.

HOW DO THEY BEHAVE? BEHAVIOR.

The Northern right whale dolphin is very gregarious and creates pods quite large. They are comprised of 100-200 dolphins although the most common number is 200. However, sometimes they form superpods up to 2,000-3,000 individuals. The organization of such pods is somehow similar to some birds; they can travel forming a V.

It often associates with other dolphins and marine mammals, especially the Pacific white-sided dolphin (Lagenorhynchus obliquidens) and the Risso dolphin (Grampus griseus). It swims very fast, and its average speed is about 25 kilometers per hour, but it has speed bursts up to 40 kilometers per hour.

Sometimes the pod creates disturbance in the surface of the water due to its acrobatics, jumps, splashes with the tail and belly. It is also a little nervous and if something disturbs it, then flees immediately.

There are reports of seasonal migrations triggered by changes in water temperature. During spring and summer, the southernmost individuals travel to the north, and the northern ones migrate south.

HOW DO THEY REPRODUCE? MATING AND REPRODUCTION.

Data on the reproductive habits of this cetacean are very scarce. They reach sexual maturity between 9.7 and 9.9 years of age, being the later in males. In the winter-early spring period, there is more birth frequency, but other researchers believe that most births occur during the summer months, between July and August.

The female gives birth every 2 or more years to one offspring whose length is 0.8-1 meter.

WHAT IS THEIR CONSERVATION STATUS? THREATS AND CONSERVATION.

Conservation Status: “Least Concern.”

The conservation state of this dolphin is “Least Concern” on the Red List of the International Union for the Conservation of Nature (IUCN). A few years ago thousands of Northern right whale dolphins (Lissodelphis borealis) were killed annually in waters of Japan, Korea, and Taiwan as result of bycatch. Today, the number of deaths has reduced, but gillnets, direct harpoon hunting and contamination of its habitat still threaten the survival of this dolphin.

Efforts to preserve this dolphin involve its inclusion in Appendix II of CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) and taking the measures recommended by the Pacific Offshore Cetacean Take Reduction Team of the National Marine Fisheries Service (NMFS) to reduce incidental fishing mortality.

References

Annalisa Berta. Whales, Dolphins, and Porpoises: A Natural History and Species Guide. University of Chicago Press, 2015.

http://www.iucnredlist.org/details/12125/0

http://www.nmfs.noaa.gov/pr/species/mammals/cetaceans/northernrightwhaledolphin.htm

Lagenorhynchus cruciger

INFORMATION AND CHARACTERISTICS.

The world of toothed cetaceans is very vast. It contains large species, small species, unusual animals and beloved animals. The hourglass dolphin is one of the lesser-known dolphins, but it is an interesting one.

The hourglass dolphin is a cetacean rarely seen but described for the first time in 1824 from a drawing made in 1820. By 2010, only six complete specimens and parts of bodies from stranded dolphins had been in research labs. Some people call them by the nickname of “marine cow” because of the similarity of its coloration with the terrestrial cows.

Order: Cetacea
Family: Delphinidae
Genus: Lagenorhynchus

HOW DO THEY LOOK? PHYSICAL CHARACTERISTICS.

Morphology.
The hourglass dolphin has a small, sturdy, plump-looking body. Its dorsal fin is large and curved backward and moderately high while its pectoral fins are broad and hooked in the case of individuals who have recently reached sexual maturity.

Weight and size.
The records of the dolphin’s dimensions are still inconclusive, but they suggest that males may be larger than females. The length of adults is on average 1.8 meters and their weight 90-120 kilograms.

Skin Coloration.
The skin of the dolphin is black and white. The coloring pattern of its skin looks like an hourglass, so from this comes its colloquial name: Hourglass dolphin. The dorsal area is entirely black, but the color is interrupted on the sides of the body, which have a white patch that starts at the head, narrows near the dorsal fin, continues backward and ends near the tail. Under this white part, there is a black band that reaches the pectoral flippers and the caudal fin. The ventral area is white, and the beak is black.

Distinctive characteristics.
The hourglass dolphin is easy to identify because of its unique hourglass-shaped pattern.

WHERE DO THEY LIVE? DISTRIBUTION AND HABITAT.

This species inhabits southern waters between the latitudes 45° south to 68° south, frequently near the Antarctic convergence. In fact, it is has a circumpolar distribution in the Antarctic region between South America and the Macquarie Island and around the province of Tierra del Fuego. The furthest sighting, in the north, occurred near Chile.

Their habitats are remote to humans. They typically dwell in deep waters and temperatures between -0.3 ° and 13° Celsius. They rarely come to the coasts and occasionally visit shallow waters.

WHAT DO THEY EAT? DIET AND EATING HABITS.

Fish, crustaceans, and cephalopods make up the Lagenorhynchus cruciger diet. If it consumes fish, it prefers lanternfish (myctophids) mainly the species Krefftichtys andersonii. If they consume squid, their favorites are those of the Onychoteuthidae and Enoploteuthidae families. Observations indicate that they like to approach plankton concentrations and partner with seabirds.

It uses its sense of echolocation to detect prey. To do it, these dolphins emit acuter sounds than those of other species of dolphins, especially clicks, so that they can find prey from farther distances.

HOW DO THEY BEHAVE? BEHAVIOR

It is a social dolphin although its pods have few members: usually, they do not exceed 6 or 8 members, still sometimes they form groups of about 60 individuals. It associates with other cetaceans such as the fin whale (Balaenoptera physalus), the Minke whale (Balaenoptera acutorostrata) and the Southern bottlenose whale (Planifrons Hyperoodon).

The hourglass dolphin swims at a speed of 22 kilometers per hour and is an energetic acrobat of the seas. It is very curious and is not afraid to approach boats, that is why they usually ride the bow waves of boats and jump out of the water enthusiastically.

During the summer months, it is frequent to see hourglass dolphins in the waters of the south. Therefore it probably makes seasonal migrations following the cold currents.

HOW DO THEY REPRODUCE? MATING AND REPRODUCTION.

Based on the reproductive processes of other species closely related to the hourglass dolphin and some observations, information about their breeding habits is known.

The age at which they reach sexual maturity is still unknown. Most births occur between August and October, the months corresponding to the Antarctic winter. The gestation period is about 12-18 months, and at birth, the calf is approximately 90-125 centimeters long.
Breastfeeding can last up to 2 or 2 ½ years, as in other dolphins.

WHAT IS THEIR CONSERVATION STATUS? THREATS AND CONSERVATION.

Conservation Status: “Least Concern.”

It is one of the few species of cetaceans that is not vulnerable because of human activities, and this is thanks to the location of its habitat far from civilization. However, their biggest anthropogenic threat could be global warming.

It is likely that the populations of this dolphin are almost intact since they have never been under a systematic hunting as most cetacean species.

For some conservation organizations, this panorama does not mean that they do not need protection, therefore CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) has included it in Appendix II of species whose trade must be under supervision. Their conservation status in the Red List of the International Union for the Conservation of Nature is “Least Concern.”

References

http://www.arkive.org/hourglass-dolphin/lagenorhynchus-cruciger/

http://www.iucnredlist.org/details/11144/0

http://www.cms.int/reports/small_cetaceans/data/L_cruciger/L_cruciger.htm

https://en.wikipedia.org/wiki/Hourglass_dolphin

(Grampus griseus)

HOW DO THEY LOOK? PHYSICAL CHARACTERISTICS.

It is a very robust dolphin, devoid of a snout. If only its dorsal fin appears above the surface of the ocean, it can be confused with a bottlenose dolphin (Tursiops truncatus) or with an orca (Orcinus orca), since the shape of its fin resembles that of orcas and Tursiops truncatus.

Weight and size.
The length of its body is on average 3 meters, but some individuals reach up to 4.3 meters. It has a body mass of 300 to 500 kilograms.

Morphology.
This dolphin has a compact and almost square head, similar to that of pilot whales (Globicephala Family), and it also lacks a beak. The anterior part of the body is sturdy but narrows towards the tail. Its dorsal fin with a sickle shape is large and curved, located in the center of the back. The pectoral flippers are long and thin and bent backward in a semi-straight line. The caudal peduncle is very narrow.

Skin Coloration.
It varies according to the age of the dolphin. Young specimens have a metallic gray or brown skin in the dorsal area and whitish in the belly. The snout has an ocher color, and between the pectoral flippers, there is a light spot with an anchor shape. As they grow, the coloration fades, and the adults appear to be almost white. They have 2 to 7 pairs of teeth in the lower jaw

Distinctive characteristics.
Its superior jaw is devoid of teeth, and on the melon, there is an external vertical groove that extends from that organ to the mouth. Another distinctive sign of the species is the presence of scar marks on the back and sides due to a lack of repigmentation and a very slow healing process.

WHERE DO THEY LIVE? DISTRIBUTION AND HABITAT.

This dolphin has a wide distribution in temperate, tropical and subtropical waters of the oceans of the world between the latitudes 60° north and 55° south. In the northern hemisphere, Scotland is the limit of its distribution, and in the southern hemisphere, it does not travel beyond the Cape of Good Hope, Australia, and New Zealand. Its distribution zones include the Gulf of Alaska, the Gulf of Mexico, the Persian Gulf and the Red Sea.

The countries that host the species include: Australia, Bahamas, Barbados, United Kingdom, United Arab Emirates, Peru, Philippines, Papua New Guinea, Madagascar, Mexico, Chile, China, Canada, United States, Cook Islands, Brazil, Cayman Islands, Argentina, Costa Rica, Haiti, India, Indonesia, Japan, Jamaica, Mozambique, Denmark, Ecuador, New Zealand, Taiwan and France.

It prefers to inhabit deep waters of the continental slope and seldom ventures to visit the coastal areas. It avoids polar waters and likes those with temperatures between 15° to 20° Celsius but can thrive in waters up to 10° Celsius. It dwells on steep slopes, edges of the continental shelf, mountains and submarine canyons.

WHAT DO THEY EAT? DIET AND EATING HABITS.

The daily diet of the Risso dolphin is composed of fish, crustaceans such as krill and cephalopods such as squid, octopus, and cuttlefish. Thier favorite food is Argonauta argo, a species of pelagic octopus.

Usually, they seek their food at night when the prey travels to the surface of the ocean, but they can submerge to depths less than 1,000 meters (their usual range is 600-800 meters) for 30 minutes to get food. Occasionally they feed in cooperation with other dolphins.
Their teeth only serve to hold their prey firmly, as this dolphin swallows its victims whole.

HOW DO THEY REPRODUCE? MATING AND REPRODUCTION.

It is very likely that Risso’s dolphin reproduces throughout the year but with regional variations. In southern Africa, for example, births occur mainly during December.

The breeding practice is not known, but the hypotheses focus on polygamy and multiple mating during the same season (polyandry). The gestation period lasts between 13 and 14 months; Subsequently, only one offspring of about 20 kilograms of weight is born.

The mother cares the calf until it leaves the pod, a few time after being weaned at 12-18 months of age.

Females mature sexually at the age of 8 to ten years, but males reach maturity around 10 and 12 years of age. Mothers give birth every 2.4 years.

HOW DO THEY BEHAVE? BEHAVIOR

Thanks to research, it is known that Risso’s dolphins spend almost 4 percent of their time resting, 5 percent feeding, 13 percent socializing and 77 percent traveling. Their migration patterns are unknown, but not all populations usually migrate.

Their pods have 10-50 members and organize according to their age and gender, being the adult female-male relationships the strongest bonds, but female groups are much larger than male ones. The latter is due to a cooperative behavior characterized by the support in caring the offspring among the female mothers. They are also able to form groups with other cetaceans.

At times, they show aggression to their companions hitting with the flippers and the tail, and they have been seen chasing bottlenose dolphins (Tursiops truncatus). They communicate through clicks, whistles, grunts and squeals and use echolocation to get an image of their surroundings.

WHAT IS THEIR CONSERVATION STATUS? THREATS AND CONSERVATION.

Conservation Status: “Least Concern.”

This dolphin has a “Least Concern” conservation status in the Red List of the International Union for the Conservation of Nature (IUCN). Nevertheless, this does not mean that they lack threats to its survival, as these include:

– Intentional catch to obtain meat for the human consumption, bait for fishing and oil.
– Bycatch.
– Reduction of their prey and food availability.
– Habitat Loss.
– Climate change that modifies its distribution and populations.

The Risso’s dolphin is still unthreatened, so it is essential to maintain its populations and improve their living conditions by reducing the impact of anthropogenic factors.

References

Jefferson, Webber, Pitman. Marine Mammals of the World: A Comprehensive Guide to Their Identification. Academic Press, 2015. Page 210.

http://www.cms.int/reports/small_cetaceans/data/g_griseus/g_griseus.htm

Gerardo Ceballos. Mammals of Mexico. JHU Press, Oct 9, 2014

Hector’s Dolphin Facts

(Cephalorhynchus hectori)

INFORMATION AND CHARACTERISTICS.

Hector’s dolphin is one of the smallest toothed cetaceans in the world and is endemic to New Zealand. This dolphin got its name in honor of Sir James Hector, a Scottish scientist who described this dolphin for the first time in the decade of 1870’s.

Order: Cetacea
Family: Delphinidae
Genus: Cephalorhynchus

HOW DO THEY LOOK? PHYSICAL CHARACTERISTICS.

This dolphin varies in size depending on its geographic location. Its subspecies, the Maui Dolphin, is slightly larger.

Weight and size.
The species presents sexual dimorphism since females are bigger than males. The average length of an adult can be in the range of 1.2-1.6 meters. The weight oscillates around 40 and 60 kilograms.

Morphology.
It exhibits a short and robust torpedo-shaped body that becomes narrower towards the caudal fin. It has large flat pectoral flippers and a rounded dorsal fin. Its snout is short and does not have a long beak. There is no set number of teeth but these, conical and with a diameter of 3 millimeters, can form a set of 31 pairs in the upper and lower jaw.

Skin Coloration.
The dorsum and sides have a light gray color with a dark stripe along the upper area from the dorsal fin to the caudal fin. The former and the pectoral flippers, as well as the tail, are black and from the snout, a dark band extends passing through the eyes to the beginning of the flippers. The lower region of the snout and belly are whitish.

Distinctive characteristics.
Hector’s dolphins are easily recognized, it just takes observing if the animal has rounded and dark fins, as well as a semilunar spot between the eyes and the blowhole. And of course, you should notice a small body size.

WHERE DO THEY LIVE? DISTRIBUTION AND HABITAT.

The Hector’s dolphin only inhabits around the South Island of New Zealand and a small region of the North Island. Its distribution is the most limited of all extant cetaceans. For habitat, it prefers shallow coastal waters with depths less than 100 meters. It lives about 7 kilometers off the coasts and can reach estuaries, river mouths, and shallow bays.

WHAT DO THEY EAT? DIET AND EATING HABITS.

There is a belief that these dolphins are generalists in their diet and they select prey species based on their size. Their prey is almost always small fish and squid, including yellow-eye mullet (Aldrichetta forsteri), Kahawai (Arripis trutta), arrow squid (Nototodarus sp.), Ahuru fish (Auchenoceros punctatus), Red cod (Pseudophycis bachus) and Yellowtail horse mackerel (Trachurus novaezelandiae).

During the spring and summer months, these cetaceans remain close to the coasts, perhaps because it is the time when their prey flock there to spawn and when the eggs hatch.

To hunt, these dolphins use their sense of echolocation in murky and shallow waters. They submerge for about 90 seconds, trap the prey and consume it. In the east of the South Island, they have more variety of food, because in this area 80 percent of their diet is composed of 8 species, while in the west 80 percent is made up of only four species.

 HOW DO THEY REPRODUCE? MATING AND REPRODUCTION.

The reproduction rate of Hector’s dolphin is extremely low: barely 2 percent per year. They breed 2-4 times a year, and females can only have up to 7 offspring throughout its life. Males reach sexual maturity at 5-9 years and females at 7-9 years of age. Both are polygamous.

Their sexual behavior lacks any aggression. On the contrary, males only search for receptive females, and when they do, court them by performing jumps, executing chases, showing the belly and establishing physical contact. These demonstrations are more frequent in groups that have more members.

Mating mostly occurs in the summer. After a gestation period of ten to twelve months, the female gives birth to a calf that starts to be independent as long as it is two years old.

HOW DO THEY BEHAVE? BEHAVIOR

This little cetacean form small groups composed of 2 to 10 individuals but sometimes these “mini pods” associate with other groups to form large temporal pods. Also, both genders have the freedom to move to other groups.

This dolphin is capable of manifesting its mood through actions and postures of the body. For example, if happy or annoyed it shakes the flukes of the caudal fin if excited it jumps out of the water, and if it bites, splashes water or forms bubbles, it is showing aggression.

It is a slow swimmer compared to other species of dolphins. They usually stay close to the coast, especially during the summer. In winter it moves away from the coast, and in the spring it migrates to other regions or returns to the coasts where it was the previous summer.

WHAT IS THEIR CONSERVATION STATUS? THREATS AND CONSERVATION.

Conservation Status: Endangered.

It is a highly threatened animal. Current estimates indicate that only about 7,400 individuals remain. It has a status of “Endangered” In the Red List of the International Union for the Conservation of Nature (IUCN), that is, in danger of extinction. The main causes of this are:

– Bycatch with gillnets.
– Collisions with boats.
– Contamination of their habitat with chemicals produced by humans that accumulate in the body of the dolphin and causes health problems and decreases fertility rates.
– Loss of habitat as a result of coastal development.
– Disturbance originated by boats that transport tourists. In this case, the impact is still under review.

In 1988, New Zealand created a marine mammal sanctuary with the aim of protecting them under the Marine Mammal Protection Act. Although dolphin deaths reduced since this, it is still not enough to recover their populations. Since 2008, the Ministry of Fisheries and the Department of Conservation in New Zealand have planned to improve conservation measures, as yet unresolved.

References

http://www.cms.int/reports/small_cetaceans/data/c_hectori/c_hectori.htm

http://www.iucnredlist.org/details/4162/0

https://www.worldwildlife.org/species/hector-s-dolphin

http://www.fisheries.noaa.gov/pr/species/mammals/dolphins/hectors-dolphin.html

]]> https://www.dolphins-world.com/dusky-dolphin/ Thu, 27 Apr 2017 05:27:31 +0000 http://www.dolphins-world.com/?p=82 Dusky Dolphin Facts

(Lagenorhynchus obscurus)

INFORMATION AND CHARACTERISTICS.

The Dusky dolphin is endemic of ​​the southern hemisphere. Charles Darwin described it during the first half of the 19th century and named it “Delphinus fitzroyi.” Although this name was later modified a couple of times, in Spanish it is still called Fitzroy’s dolphin.

HOW DO THEY LOOK? PHYSICAL CHARACTERISTICS.

The Dusky dolphin is a somewhat small species that bears a great resemblance to the Pacific white-sided dolphin (Lagenorhynchus obliquidens). Even so, scientists confirmed that they are different species from each other, and it is possible to differentiate them by carefully observing the external appearance of each species.

Order: Cetacea
Family: Delphinidae
Genus: Lagenorhynchus

Weight and size.
It is a dolphin whose distribution is not continuous, so its size varies among populations. In New Zealand, the females have a length of 1.67-1.78 meters and a weight of 69-78 kilograms. The males, meanwhile, are between 1.65 and 1.75 meters and weigh between 70 and 85 kg.

Morphology.
The dusky dolphin has a sturdy body with a small head tilted down and a rather short snout, almost nonexistent. The shape of the melon is very noticeable under a bulging forehead. It has a large dorsal fin slightly hunched back with two colors, long pectoral flippers and a caudal fin with flukes split by a central notch and with curved edges.

Skin Coloration.
This species has a very distinctive color pattern with a dark bluish or black dorsal area and a light gray or whitish ventral region. But that is not all; The bicolor dorsal fin has dark edges in the front that blend into a light gray color that fades towards the back. The face is white or light gray until the forehead wich is black, and the snout and the lower jaw are also back as well as around the eyes. The pectoral flippers tend to be the same dark color in the front but less intense and blend into white or light gray in the back.

Distinctive characteristics.
The coloring pattern might not be so unique if it was not for the two whitish stripes that start from the tail and extend to the dorsal area. Also, the eyes have a dark “patch” around them. The bicolored dorsal fin is also a distinctive feature.

WHERE DO THEY LIVE? DISTRIBUTION AND HABITAT.

It is only possible to find this mammal in the southern hemisphere around some coasts. It has a circumpolar distribution in regions of Australia, New Zealand, Tasmania, Central and South America, Southwest Africa and Campbell Islands, Tristan de Acuña, Prince Edward, Amsterdam, Malvinas, and Chatham.

It is natural to find this species near the coasts, because, it is a coastal dolphin. It inhabits the continental shelves and slopes of cold waters or shallow areas with temperatures of 10° to 18° Celsius.

WHAT DO THEY EAT? DIET AND EATING HABITS.

The amount of food they consume varies according to their size and habitat but in general, is based on small fish such as anchovies and hake as well as on squid and shrimp. The most common thing is that it feeds on the surface, but they also do it on the seabed.

They perform acrobatic jumps in the air, and they submerge up to 150 meters deep.

These dolphins prefer hunting at night. This activity is carried out cooperatively in large groups of up to 300 individuals as they establish organized strategies to perform an efficient hunting.

The feeding habits of the dusky dolphin also depend on the region where they inhabit. In Argentina, the members of pods make patterns of slow movements and short dives during the night, and at dawn, they begin to look for food. In New Zealand, they perform jumps and stunts in the air and dive to depths of up to 150 meters. Then they chase and strike the prey very noisily. Every population developed different ways to feed.

HOW DO THEY BEHAVE? BEHAVIOR

The Dusky Dolphin is an expert acrobat who enjoys playing and jumping out of the water. Also, it can make high jumps and elegant leaps in the air, usually including most members of the pod. It is quite a show to see the groups jumping coordinated with each other; This happens regularly before and after feeding. This dolphin is also very curious. It is frequent to find it near the boats and following the bow waves.

The social structure of the pod of 50-500 members (although there are groups of up to 1,000 individuals) segments into young, mothers with offspring and sexually mature adults. During the day they can stay in smaller groups until the morning when they go into deeper waters and start looking for food.

Although this dolphin can travel long distances, it is not considered a migratory species.

HOW DO THEY REPRODUCE? MATING AND REPRODUCTION.

It has a polygamous mating system; this dolphin maintains transient relationships with multiple partners throughout its life. The age for reaching sexual maturity is variable; In New Zealand, this happens when the dolphin is between seven and eight years old, and from that age, the dolphin joins groups of mature males to begin mating near the coasts. In Peru, sexual maturity is between 3.8-5 years old, and in Argentina, a female is mature at 6.3 years.

After a competition for a particular partner, the successful male may breed during the spring. After a gestation period of approximately 11-13 months, a single offspring is born during the summer in New Zealand and Argentina and winter if the dolphins inhabit the coasts of Peru. Three years later the calf is weaned.

WHAT IS THEIR CONSERVATION STATUS? THREATS AND CONSERVATION.

Conservation Status: “Data deficient.”

Historically, the dusky dolphin has been a cetacean subject to both incidental and intentional catches which have contributed to the decline of their populations. In Peru, the problem is worrying since thousands of these dolphins are killed each year for human consumption. For example, they killed 7,000 dolphins in the period from 1991 to 1993! A very high number that does not meets the standards of sustainable fishing.

On the other hand, bycatch due to gillnets and other fishing gear, reduces the populations dramatically, especially in Argentina and New Zealand. The contamination of waters near the coasts, where these dolphins dwell, and their low reproduction rate also contribute to having a negative forecast.

In 1990 the government of Peru banned the direct hunting of any cetacean, but the law is apparently not respected. For its part, CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) included the species in the group of animals whose trade needs regulation. The Red List of the International Union for the Conservation of Nature (IUCN) does not have sufficient data to make an assessment of its conservation status.

References

William F. Perrin, Bernd Würsig, J.G.M. ‘Hans’ Thewissen. Encyclopedia of Marine Mammals. Academic Press, 2009. Page 335.

Jefferson, Webber, Pitman. Marine Mammals of the World: A Comprehensive Guide to Their Identification. Academic Press, 2015. Page. 293.

http://www.iucnredlist.org/details/11146/0

http://www.doc.govt.nz/documents/science-and-technical/drds270.pdf

Dolphins are mammals fully adapted to live in the water. For this, they developed several adaptations during their evolution.

The migration of dolphins to the aquatic environment was a process that lasted millions of years. Moving from the terrestrial to the aquatic habitat entailed a series of adaptations without which this would not have been possible.

Physiology is the science that studies the functions of living beings. In the case of dolphins, it is interesting to know how they perform their physical and chemical functions in their changing environments.

HOW DO DOLPHINS REGULATE THEIR TEMPERATURE?

Dolphins should maintain a constant body temperature of about 36°-37° Celsius degrees.

Dolphins need to keep a body temperature of about 36°-37° Celsius degrees. As they do not have a coat to protect from the cold temperatures of the water, they must regulate their internal temperature in other ways; this process known as thermoregulation is vital for their survival.

Dolphins perform body thermoregulation through a set of internal resources that evolution provided them. Initially, the fat in their body is a thick layer that insulates the inside from the cold water. This layer allows dolphins to retain their body heat. Secondly, their flippers do not contain fat, but instead, they have a lot of veins so that the heat of the blood that runs through the arteries transfers to the blood of the veins. This process is a heat exchange system.

In hot environments, dolphins increase blood flow to their limbs. The veins and capillaries expand, and this way excess heat can be released.

HOW DO THEY SWIM?

The fusiform and hydrodynamic body of dolphins is perfect for reducing water resistance when swimming, which allows them to save energy. Contrary to fish, these cetaceans swim by moving the tail from top to bottom and not from side to side. Their tail has a strong propulsive force, and the flippers are useful to direct their movements.

Typically they do not need to dive very deep, but they can do it for a few minutes to obtain food if needed. Dolphins that inhabit the cooler waters are better suited to dive deeper, as they have more body fat. Besides the time their need to resist down without breathing, the water temperature dramatically drops in places where the sunlight does not reach.

When dolphins dive, their heart rate slows down, and protein molecules take care of providing oxygen to the body tissues.

One of the most evident differences between cetaceans and fish is their swimming method. Fish swim by wiggling left and right, and if you watch crocodiles and snakes, you’ll see the same motion. However, as dolphins are mammals with a different skeletal structure, they make up and down strokes to swim.

Today you can still see some of the remnants of their terrestrial ancestors in the dolphin’s skeletal structure. For instance, they have forelimbs, which became flippers with shortened arm bones and no fingers. Hind limbs exist as vestigial skeletal remains. Most cetaceans, including dolphins, still have a pelvis typical of land animals.

HOW DO DOLPHINS BREATHE?

Dolphins, like other mammals, get the oxygen from the air instead of the water and thus use lungs instead of gills. A dolphin that cannot surface and breathe will drown; this is why dolphins caught in fishing nets die.

Like all mammals, dolphins have a pair of lungs that process the air that they breathe in through their blowhole. That’s why most Dolphins stay close to the surface of the ocean.

Unlike humans that do it instinctively, dolphins have to reach the surface to breathe consciously. When they do this, the blowhole opens to allow the air in and closes when they get back into the water.

The lungs process the air and take the oxygen from it releasing it into the bloodstream and when exhaling the lungs release the carbon dioxide from the blood into the environment.

How do dolphins breathe?
Blowhole.

HOW DO DOLPHINS SLEEP?

As mentioned above, dolphins breathe consciously. Therefore, their brain needs to give the order to reach the surface to get air continuously. As a consequence, they could not sleep until unconsciousness as humans do. Otherwise, they would drown and would be vulnerable to predators.

Dolphin blowhole does not expel a stream of water, it looks this way, but it is only water vapor that condenses in the air when they exhale.

The solution that evolution found for dolphins is that while resting, they have to keep a cerebral hemisphere active to consciously breathe and to stay alerted from dangers. However, the versatile adaptations of dolphins to changing environments is fantastic, because researchers found that captive dolphins apparently have a deeper sleep than dolphins in the wild since they do not react to minor external stimuli while sleeping.

Incidentally, there is a wrong belief that dolphins and other cetaceans expel a stream of water from their blowhole, but this is not the case. It is only water steam that condenses in the air when they exhale.

Blowhole.

HOW DO DOLPHINS REPRODUCE?

The reproduction of dolphins is sexual, and the fertilization is internal. Both males and females have the reproductive organs concealed inside slits in their body. Mothers have the mammary glands also hidden inside slits.

The gestation period has a similar duration to that of humans and females give birth to live and developed offspring, which are fed with breast milk and cared for over a relatively extended period. The relationship between a mother and its offspring lasts forever.

WHAT SENSES DO DOLPHINS HAVE?

They have some of the traditional senses that we have: hearing, sight, taste, and touch, but evolution provided dolphins with an additional sense that only a few animals have: echolocation or biosonar.

Dolphins produce sounds that emit forward and interpret the echo that returns to them with the aim of discovering prey, navigating, communicating or detecting dangers.

Probably one of the most relevant differences between land mammals and dolphins is the way they vocalize. While most terrestrial animals have a larynx or a similar structure to vocalize using throat vibrations and exhaled air. Dolphins and other cetaceans use other organs to make high-pitched sounds either for echolocation or regular communication with others members of the pod.

Regarding the other senses, dolphins do not have external ears, but they have a good hearing capacity with an internal ear that receives sounds through the throat.

Also, Dolphins have a vision much better than one might expect of an animal that uses echolocation as its primary way of sensing the world. Despite this, dolphins can see little or no colors and have limited binocular vision like primates. Their eyes are small but even though they have a good sight with a reduced capability to distinguish colors.

They have an excellent sense of touch improved in some species with sensible hairs and frequently used for social purposes.

Dolphins do not have olfactory lobes. Therefore they lack the sense of smell.

Finally, their sense of taste is not especially good because they do not have a very developed taste buds, but they show some preferences to certain fish species which could be an indicator of taste, although this could be an intuitive behavior because some types of fish have better nutrients for them than others.

These organs and senses are the structures that help these cetaceans to keep in perfect harmony with its context.

References

https://dolphins.org/physiology

Coates, Linda. How to Make a Dolphin: Anatomy, Physiology and Taxonomy (English Edition).

Knut Schmidt-Nielsen. Animal Physiology: Adaptation and Environment. Cambridge University Press, 1997.

The overall anatomy of the dolphin is designed to survive in the water. All dolphins have similar anatomical and morphological characteristics; this means that all species have some features that do not differ widely between species.

Obviously, there are differences in skin color, shape, size and weight but it is relatively easy to recognize that a particular animal observed is a dolphin. However, it is common to confuse porpoises with dolphins, and this is because their external appearance is very similar and both are cetaceans closely related. The difference is that porpoises are smaller animals and have rounder snouts than dolphins.

Their size can range from one extreme to the next. Some of the smaller ones are about 4 feet in length, and others measure as long as 30 feet. Some of them weigh about 90 pounds while others tip the scale around 11 tons.

The coloring of dolphins is mainly grayish blue, brownish or black and white. They have a very sensitive skin, which can get easily harmed if hit by rough surfaces. However, they can recover pretty fast from severe injuries, including shark bites because they have a rapid healing process even for deep wounds.

Their skin feels like rubber, and they don’t have any sweat glands. Part of this though could be due to the thickness of the skin of a dolphin. The epidermis, which is the outer layer of skin, is from 10 to 20 times thicker than that of other terrestrial mammals. The skin will peel and flake off for new skin cells to replace the older ones.

The bone structure of a dolphin.

Dolphins have a streamlined body designed to swim very fast, even for extended periods of time. The tail of a dolphin has two parts called flukes, and they use them to propel their body through the water, using their pectoral flippers to swim in a given direction.

Dolphins have a blowhole at the top of their head, and they must come to the surface for air. Some of them need to breathe several times a minute, and some species only have to get air twice per hour. They also have a large brain, the second largest for mammals in comparison to their body size, only after humans. Their brain is very complex, and research shows it to be more advanced than that of other animals.

What anatomical features characterize a dolphin? Let’s see:

GENERAL FEATURES

– Weight and size.

Dolphins vary in weight and size. There are small species as the Maui dolphin, which measures on average 1.7 meters in length and weighs about 50 kilograms, and there are large species that reach 5 to 8 meters in length like the Orca (Orcinus orca) which, by the way, is the largest and heaviest extant dolphin.

– Skin color.

The skin of dolphins feels soft to the touch although it has a thick epidermis covered with a thin layer of cornified cells. Despite this, it is extremely sensitive due to a large number of nerve endings it has on the exterior. Given this fragility, it damages very easy with any contact of a rough surface and even human fingernails, but if this happens, the healing process is fast and develops a dark scar in the tissue, which later turns white.

Beneath the skin, there is a thick layer of fat that dolphins use as an energy reserve in periods of food shortage, as an insulation to prevent heat loss in cold environments and as a resource that helps maintain the hydrodynamic shape of their body.

Most species have a gray or bluish color on the dorsal area and white or light gray in the ventral area. This coloration is particularly useful for camouflage because if you see a dolphin from above, its dark skin is confused with the ocean floor while when seeing it from below, the color of its belly is similar to the ocean surface, brightened by the sunlight.

However, not all species have the same color pattern described above. The Amazon river dolphin (Inia geoffrensis) has a pink color on its skin, therefore is known as the “pink dolphin.” Also, some species have stripes or spots of different sizes, colors, and shapes.

Skeleton.

The bone structure of dolphins is lighter than that of terrestrial mammals as it has to withstand less weight in the water. Dolphins have an adjustable rib cage, thanks to which they can swim in low-pressure environments without suffering damage. The neck is rather short because the seven cervical vertebrae are fused together.

The skeleton still retains vestiges of a terrestrial life, like a pair of floating bones under the backbone that should have been a pelvis.

On the other hand, the body of the dolphins is fusiform and hydrodynamic, perfectly adapted to life in the water. It has three main parts, head, trunk and tail, which include other elements.

External anatomy of a common dolphin.

Head

Brain.
The brain of these cetaceans is large, and its mass is slightly greater than that of humans. It is 15-60 times bigger than the brain of a shark of similar size.

Eyes.
Located on each side of the head, they provide a broad field of view and are very sensitive despite the inability to identify colors. They can move independently of one another, but they are not able to look directly up or down.

Ears.
Dolphins do not have external ears, but they have small openings behind the eyes, which lead to an ear canal.

Blowhole.
It is the orifice located at the top of the head that serves to breathe and to make sounds. It has a kind of muscular membrane that prevents water from entering the body when the dolphin is submerged.

Melon.
It is a spherical organ located in front of the skull, used for echolocation. The rounded shape of this mass of adipose tissue is what gives dolphins the shape of their forehead.

Mouth.
Located in the front area of ​​the head, it has several teeth whose number varies according to the species, but they are around 80-100. The jaws are elongated and play a significant role in the sensory system of the dolphin.

Trunk

Dorsal fin.
It is on the top of the dolphin; they only have one dorsal fin that gives them stability when swimming, preventing them from spinning involuntarily in the water. There are a couple of species that lack this dorsal fin.

Flippers.
In the lower part of their body, dolphins have two pectoral flippers which are curved, useful for directing and controlling movements and speed when swimming.

Lungs.
Like all mammals, dolphins have lungs and breathe air. They are the organ of the respiratory system which process the air inhaled through the spiracle. Unlike humans that do it instinctively, dolphins breathe conscientiously.

The orca is the largest and heaviest dolphin.

Stomach.
It is just in the middle part of the body, and it has several sections.

Intestines.
Just as in other mammals, they serve to absorb nutrients from the food and remove the unused material from it.

Bladder.
It is nearly at the end of the trunk, and it is tiny.

Post-anal hump.
It is a protuberance in the lower part of the body only found in adult males.

Genitals.
Also in the inferior part of the body, the genitals of dolphins are hidden in slits. Males have two slits that conceal the penis and anus, while the females have only one that contains the vagina and anus, and two mammary slits on both sides of this one.

Tail

Peduncle.
It is the narrow section that connects the flukes with the rest of the body.

Caudal fin.
They function as a propellant when swimming. It moves from top to bottom and not from side to side as in the case of fish.

Flukes.
They are the two sections of the caudal fin.

OTHER ANATOMICAL ADAPTATIONS.

Sleeping.
Dolphins do sleep, but it may not appear that way when you observe them; This is because only one hemisphere of the brain will rest at a time. The other allows them to be alert for dangers and to reach the surface for breathing at regular intervals.

Another unique characteristic of the dolphin anatomy is that they don’t have hair covering their body; They may be born with a few hairs, but they lose them soon after being born.

References

https://dolphins.org/anatomy

http://www.sciencedirect.com/science/article/pii/0361923080902725

Cozzi, Huggenberger, Oelschläger. Anatomy of Dolphins: Insights into Body Structure and Function. Academic Press, 2016.

http://oceantoday.noaa.gov/dolphinanatomy/