Bottlenose dolphin
Since antiquity the dolphin has been a friend of the human. A word “dolphin” is ancient and derives originally from Greek “delphis” that means “womb” – a well of life. Greek god Apollo could change himself into a dolphin and heading a pod of real dolphins he saved people shipwrecked near Delphi. Another Greek god Poseidon, Master of the Seas, was always pictured beside a dolphin. Dolphins were involved in life of human, too. This is a legend about it.
In Corinth lived a musician named Orion. One day he won a gold prize on the competition in Sicily and returned home on shipboard. But the ship was attacked by pirates who took the prize from Orion and told him to throw himself into the sea. The Orion asked them to let him sing his last song. His song was so beautiful that attracted dolphins and they followed the ship. When Orion threw himself into the sea, dolphins saved him and on their backs carried him ashore.
This story is only a myth. But dolphins indeed followed ships playing on the bow waves of ships as if they were dancing to the strains of lyre. So why do dolphins always attract our attention? Maybe because we consider them the smartest animals. As well as people, dolphins are mammals. They are warm blooded, live bearing, have lungs and nurture their babies with milk.
Origin
Who was an ancestor of dolphins?
Dolphin skeleton has rudimentary pelvic bone and scapulas, one of the main features of gastro-intestinal tract of cetaceans is a multichamber stomach, the same as ruminant animals have. This fact and many other features bring us to the conclusion that ancestors of dolphins lived onshore.
Some scientists consider hoofed mammals as ancestors of dolphins, as both have bicornuate uterus, multichamber stomach, multilobar kidneys, much in common with genital system structure and blood chemical composition. According to remains, remote ancestors of marine mammals lived onshore about 70 million years ago, but about 50 million years ago they moved in water.
They had to overcome a lot of obstacles: water is less suitable for air breathing, warm blooded animals nursing babied with milk. Water density is much higher than air density, thermal conductivity is very high. When you go down, pressure rises, lightness decreases. And they need to hunt, catch prey, breath while rising on the surface and protect respiratory organs from water.
As a result of millions years of evolution dolphin’s ancestors lost their hair-covering, their bodies got streamlined shape as they needed to overcome water resistance 800 times higher than onshore, their hind limbs being of no use disappeared, instead of them fluke (propulsion) had formed, and fore limbs became flippers (elevation and turn rudders), organs of sense and physiology changed.
In spite of inner and outer change cetaceans retained all features that mammals have. They just became mammals that returned into water, and were called secondary aquatic animals. The modern shapes of dolphins are traced in remain of about 5 million years ago.
Scientific classification
All animals nursing their babies with milk are combined in the class of MAMMALS (Mammalia). Mammals adapted to aquatic life are combined in the order of CETACEANS (Cetacea).
The order is divided into 3 suborders:
1. Primitive whales (Archeoceti)
A suborder disappeared almost 30 million years ago and known only by fossils. Some species reached large sizes.
2. Baleen whales (Mysticeti)
A suborder of cetaceans which is characterized by large triangle baleen plates for water filtering instead of teeth. Purl edge of plates forms a sieve cover for plankton filtering. There are main species: blue whale, gray whale, great polar whale, fin whale, etc.
3. Toothed whales (Odontoceti)
These are cetaceans which have teeth. They eat fish and squid. The main species are cachalot, killer whale, pilot whales, white whales, etc.
Toothed whales are divided into several families. All dolphins are combined into the largest family of DOLPHINS (Delphinidae).The family numbers more than 30 animal species.
Different dolphins differ from each other not only by size and colors, but also by habits of life. Some of them live only in particular places and some - nearly all over the world. In the Black Sea 3 species live – bottlenose, white-bellied porpoise and Azov dolphin.
The biggest Black Sea dolphin belongs to Turpsios truncatus species, which is also called bottlenose dolphin. These dolphins are the most popular in oceanariums.
Bottlenose dolphins in general are not Red-book species, but the Black sea bottlenose dolphins’ population in particular is included in endangered-species list of Russia.
It’s unknown how many bottlenose dolphins all over the earth. Populations of only several areas are estimated now.
In the Mexican shelf their number is about 67000, in the western Pacific Ocean and in Japan – about 35000, in USA water area and in the western Atlantic Ocean – 11700, in the Mediterranean Sea are about 10000 dolphins. Estimation of the Black Sea dolphins is very incorrect.
Habitat
Bottlenose dolphins may be divided into two ecotypes (forms):
1. Coastal ecotype is adapted to warm, coastal waters. They have smaller bodies and long flippers suggesting maneuverability and heat dissipation. These dolphins love in marine havens, gulfs, bays and river deltas.
2. Offshore ecotype is adapted to cold and black waters. Their large bodies retain heat and help to protect against predators.
Migration
Seasonal changes in water temperature, migration of fish another prey may account for the seasonal movements of dolphins. Some species migrate regularly within either Northern or Southern hemisphere, other migrate on longer distances but less regularly and without regard to seasons (false killer whale, pilot whale), and some lead sedentary life staying in “home” region (area of daily life).
Physiology and anatomy
Size
Usually males of the Black Sea bottlenose dolphins are larger, heavier, with longer bodies comparing to the females. But females grow faster in the first decade of life. The longest registered body length is 310 cm. Adult animals attain weight of 150-250 kg.
Sizes and body shape of the animals vary by geographic location. For instance, coastal dolphins are smaller than offshore ones with their large bodies. Dolphins of the Pacific Ocean may be larger than the Mediterranean ones.
Coloration
Bottlenose dolphins are generally slate grey to charcoal color on the back melting into white on belly and lower jaw. Belly may be even pinky. Sometimes the aged animals have brush markings on sides and around belly. Coloration of dolphin is a camouflage that helps conceal dolphins from predators and prey. When viewed from above, a dolphin’s dark back blends with the dark depth water, and when seen from below, a dolphin’s lighter belly blends with the bright ocean surface.
Body shape
Dolphins have sleek, flexible, fusiform, streamlined bodies ending with horizontal tail fin (fluke) in form of wide isoscales triangle divided into two blades. This is the main propulsion source of dolphin. Pectoral fins provide directional control during turns and slowing. Dorsal fin, possessed by many species, provides stability while swimming.
Pectoral fins
Fore limbs of dolphin’s remote ancestors transformed into pectoral fins or foreflippers which are paddled, streamlined and drop-shaped providing maneuvering in water. Pectoral fins retained a skeletal structure of typical five-toed mammals’ limb. Pectoral fins are used for motion control and slowing. They also are very important for thermoregulation.
Fluke
Hind limbs of dolphins’ ancestors grew less, became useless and finally disappeared during the evolution. Propulsion function was imposed on two horizontal tail outgrowths called fluke. Tough and hard fluke consists of fibrotic connective tissue, with no muscles and bones. Tail swing is about 20% of body length.
Tail stem moves up and down. Blades angled to steam axis: when the stem moves down, blades move up and vice versa. Tail does not rotate while swimming. As well as pectoral fins fluke is very important for thermoregulation
Dorals fin
As well as fluke, dorsal fin consists of fibrotic connective tissue with no bones and cartilage. It may serve as a keel, bur obviously is not obligatory structure as some species of dolphins (white whale) lost dorsal fin. Bottlenose dolphins’ dorsal fin is slightly back recurved, diversiform. The same as pectoral fins and fluke, dorsal fin is very important for thermoregulation.
Head
Head is positioned on short and rigid neck. Dolphin’s neck is much shorter comparing with land mammals (about 4% of body length). The cervical vertebrae of the Black Sea bottlenose dolphins are fused together that is typical for the most part of toothed cetaceans. The cervical vertebrae of some species are combined in cervical block, and the head, consequently, becomes almost moveless. 7 cervical vertebrae of river dolphins and white whales are free, and the head can turn at the angle of up to 45 degrees with respect to the body.
The fore part of dolphin’s face formed by jaws is called rostrum, or snout, or beak. Usually its length is about 7-8 cm. Due to protrusive rostrum dolphin’s head is conical and sharp-formed, that may be compared with bottle neck. For that reason the dolphins are called bottlenose.
Dolphin has sharp conic teeth up to 10 mm in diameter. They are not supposed for chewing, but for catching and holding of the prey. All teeth of bottlenose dolphins, as well as most toothed whales, are similar and differ only in size – front teeth are smaller. The most of species have 20-25 teeth on each side of upper jaw and 18-24 on each side of the lower. A total number of teeth are from 76 to 98.
Eyes are located at the sides of the head. There are glands at the inner corners of the eye socket which secrete a jelly mucus that lubricates eyes, washes away debris and renders eyes safe from infection.
Dolphins have unpaired spout-hole (blowhole) located on the top of the head. It’s closed by skin-muscular flap and opens only for short breathing – simultaneous air exhale and intake. When blowhole is closed, its muscles are relaxed, and in order to open it, dolphin tenses valve muscles.
It seems that cetacean including dolphins do not perceive smells.
Dolphins’ ears, as well as all cetaceans, are located behind eyes with no external ear flaps. External ear canal is a small hole of S-tube form (bottlenose dolphins have imperforated hole). Diameter and form of hole change throughout its duration. The length of the whole acoustic channel is about 5,7-6,0 cm.
External world perception
Hearing and sound perception
Dolphins have well-developed hearing, they easily perceive and produce sounds. Volume of their brain divisions responsible for hearing is 10 times larger than human’s (with equal brain volumes).
The same as all mammals, dolphins perceive sound waves by cochlea located in bony labyrinth of middle ear. Middle and internal ears of dolphins are not integrated into osteocranum compared to land animals. Sound perceiving parts of the middle ears are independent units, called bulla - "bullа tympani", located in a special bone stock and connected to skull by means of short and thick tendinous connection. As a result both ears are independent receivers adapted for directional reception of sound source. Bottlenose dolphins perfectly determine place where fish jumped by splash of water. Between bulla and skull is a special cavity filled with air or fat emulsion foam located for better protection. The foam consists of micro air bulbs which perfectly isolate sound. As a result all sound vibrations coming from bones of skull do not reach inner ear. The only way to reach cochlea lies through external ear and auditory ossicles.
There are several ideas now explaining acoustic signals flow into the inner ear. A number of scientists consider that sound vibrations pass through soft tissue of animal’s head and then come through acoustic channel, eardrum and auditory ossicles into cochlea.
Other scientists believe that sound perception is realized through fat filled cavity of lower jaw bone. Sound pass through jaw to middle ear ossicles, then to inner ear, and finally acoustical nerves send nerve pulses to auditory center. Bottlenose dolphins’ acoustical nerve has more than 7000 fibers that is twice as much as human has.
Middle ear cavity of dolphins is filled with connective tissue with a large amount of blood capillaries that regulated pressure in the middle ear while swimming.
The hearing range of bottlenose dolphins is 1 to 150 kHz (middle hearing range of a human is only 0,02 to 17 kHz). Dolphin hears best within a range 40 to 80 kHz.
Sound production
In water dolphins emit different sounds at different times and depths: click, trill, grunt, squeak, whistle and screak. They use sound for communication, navigation, hunting in dark and muddy water with poor visibility. The sound produced are different in loudness, frequency and character. The last researches show that the most sounds are generated in supracranial part of nasal passage where a system of paired air sacs is formed. When the air passes through the channels between the sacs, intersections vibrate and generate different sounds.
Bottlenose dolphins produce sounds within the range 0,25 to 150 kHz. Lower frequencies (0,25-50kHz) in form of whistles are obviously used for communication. Dolphins identify each other by whistles. Mother can whistle to her baby-dolphin for a continuous period of several days after birth, and baby memorizes this sound to recognize his mother later. High frequency cracks (40-130 kHz) are obviously used for echolocation. Echolocation cracks peak is within 100 kHz range, but depending on echolocation aims frequency may change.
Echolocation
Some animals (cetacean and most part of bats) have an amazing for human ability to “see” objects in complete darkness sending high-frequency sound waves and “listening” to the echo returning. This ability is called echolocation, and this is a very important for animals way to orientate in space and receive information of the world around. Dolphins often use echolocation ability in the wild.
Echo gives them exact information about objects’ location, size, form and material. Dolphins use for echolocation short broad band pulse which differs in duration from echolocation signals of land animals. Duration of dolphins’ pulses is 7-100 mcs. Pulses pass through the frontal part of dolphin’s head called “melon”. Melon consists of connecting tissue and fat and works as an acoustic lens for sound focusing.
Sound waves propagate in water at a speed about 1,5 km/s (4,5 times faster than in the air). They reflect from an object and return back to animal in form of echo.
A time period between a click and echo returned indicates a distance to any object on the way. The most effective echolocation is in the range 5 to 200 meters for objects of 5 to 15 cm in diameter. Dolphin can identify size and form of the object. It helps them to recognize a prey they prefer. But researches show that sightless dolphin spends more time for echolocation.
For echo signals processing a highly-developed brain is required. That’s why dolphin’s brain divisions managing hearing are 10 times larger than human ones. But there are still many details unknown and scientists continue their investigations.
Vision
It may be said that dolphins see the world around mostly by one eye – they are monocular. They can see by two eyes only in a very narrow range of vision – about 12 degrees forward and down from head.
Dolphins have acute vision both under water and in the air. Retina of cetacean has two areas of good visibility (human eye has only one), one – for clear vision in water and another – in the air.
Dolphin’s pupil has very unusual structure: when it’s constricted, an arc-shaped fissure is formed which then turns into two narrow holes working as a camera lens diaphragm and, thus, increasing focusing depth and correcting defects of the eye reflecting system .
Dolphin’s retina contains two types of cells: rod cells and cone cells, indicating that they can see both in darkness and in bright light. Their eyes have a well-developed cell layer which reflects light though the retina a second time, improving vision in low light.
Tacktile
Anatomic and behavioral researches suggest that bottlenose dolphins have a well-developed touch sensibility. Their skin is very sensitive in a broad range and contains much more nerve-endings comparing to human.
Taste
Little is known about dolphin’s sense of taste. Brain and skull nerves features suggest that dolphins may have some taste sensation. Dolphins also have strong preferences for specific species of fish that convinces of dolphins’ taste.
Researchers have found that dolphins have taste buds at tongue. According to experiments dolphins perceive weak concentration of some matters in water which proves chemoreception of toothed whales.
Smell
Olfactory lobes of the brain and olfactory nerves absence of all toothed whales indicates that they do not have a sense of smell.
Adaptation to water environment
Breathing
For life in water and air breathing ancestors of modern dolphins had to change the entire respiratory system. Respiratory system and digestive system of toothed whales are completely isolated.
Outer breathing spout – blowhole is on the highest point of dolphin’s head and is covered by skin-muscular fold.
Unlike land mammals, dolphins start breathing cycle from exhaling. They open the blowhole and begin to exhale when the head is shown above water. Signal for this is change of environment from water to the air (reflex respiration control). Then dolphin quickly inhales and relaxes blowhole muscles to close it.
Blowhole muscles are relaxed in the closed position. Exhaling and inhaling together take less than 1 second. Rapid air change in lungs is also an adaptation for water environment. Average respiratory rate is 2-3 respirations (exhaling-inhaling) per minute. When dolphin exhales, marine water around the blowhole is removed by air stream. But even if water gets into air passages, it is thrown out by way of blows of water and condensed vapor.
Upper air passages of toothed whales have two barriers for air passages isolation from the outer environment. The first one is a skin-muscular folded flap located in supracranial respiratory passage to which the blowhole opens. Prominences of one fold get into pits of other. The second barrier is a nasopalatine sphincter located in the area of inlet to larynx.
Trachea and bronchi were short that accelerates respiration. Dolphins have more and larger alveoli than land mammals.
During respiration a dolphin exchanges about 89% of air in lungs. This is much more efficient than humans, who exchange only 17%of air in their lungs with each breath.
Diving
Dolphins hunt in water layer or near bottom area. Depending on habitat, dolphins regularly dive at the depth 3 to 45 meters. But they are able to dive at much greater depths. During experiments dolphin dove to 547 meters. And according to studies bottlenose dolphins can stay underwater for 6-7 minutes. As a result of evolution dolphins have special physiological adaptation for diving. Dolphins can’t renew air stock underwater. Dolphins are specially adapted to save air underwater:
• Large lung volume. Dolphins’ lung mass is 2,2-2,9% with respect to the body mass (human’s relation – 0,7%), air capacity factor of dolphin’s lungs is 2,5 times higher than human’s.
• Higher blood volume. High concentration of hemoglobin* in blood (according to S. Ridgway oxygen capacity of blood is 1/4 - 1/3 higher than human has). Mioglobin** concentration in tissues is 4-9 times higher than of land mammals. Dolphins use little oxygen while diving, they have slower heart rate, blood is shunted away from tissues tolerant to low oxygen level and supplied toward heart, lungs and brain which require constant oxygen. Metabolic rate becomes lower.
• High volume of fat tissue which dissolves more oxygen than tissue fluids do.
Dolphins also have a protection against barotraumas. They have flexible ribcage which can collapse with the water pressure, very elastic lungs tissue which is adapted to fast collapse and expansion.
* Hemoglobin – blood protein transporting oxygen and carbon dioxide.
** Mioglobin - oxygen-binding protein storing oxygen in order to prevent oxygen deficiency in muscles.
Swimming
Dolphins are one of the fastest ocean inhabitants. It’s obvious, because they must outrange fish they eat. Usually dolphins swim at speed 5-11 km/h. But they can reach much faster speed while hunting. Ergometric researches showed that maximum (burst) speed of bottlenose dolphins is 29 to 35 km/h. But high-speed swimming continues in just seconds.
Thermoregulation
Water thermal conductivity is 25 times higher than the air. High thermal conductivity of water influenced on formation of characteristics providing efficient thermo regulation. Dolphins have thick layer of blubber under their skin which serves for isolation and as an energetic reserve. Blubber is usually 18-20% of body mass. Breathing habits of cetacean have meaning for inner heat storage. Infrequent respiration and breath holding while diving reduce heat dissipation.
Fusiform of body and reduced size of limbs decrease area of surface exposed to the external environment. Dolphins which live in cooler, deeper water have usually larger bodies and smaller limbs than coastal dolphins living in warm water.
Dolphin’s core body temperature is about 36-37 ̊ C and blood circulatory system is adapted to conserve or dissipate heat and regulate body temperature.
The main organs of thermoregulation of bottlenose dolphins are dorsal, pectoral fins and fluke which supplied with blood vessels. Arteries in the flippers, flukes, and dorsal fin are surrounded by veins which form complex vessels. Complex vessel consists of thickwalled muscular artery and venous coil of thinwalled veins around the artery. This vasculature is called a countercurrent heat exchange. Thus, the most heat brought to fins through arteries is transferred to the venous blood and then to internal organs rather than the environment. This system provides minimum heat loss and aids in conserving body heat. In case of overheating blood circulation through near-surface vessels increases and, thus, the organism is cooling. If it’s a need to save heat, arterial blood stream to fins decreases.
Bottlenose dolphins have a higher metabolic rate than land mammals of similar size. This metabolism generates a great deal of body heat.
Sleep
When studying sleep in bottlenose dolphins, researchers found that dolphins spent about 33% of a day sleeping. Dolphins are not moveless while sleeping compared to land mammals, they can sleep and swim. Native researches have shown that deep sleep of bottlenose dolphins may occur in only one brain hemisphere at a time. There is no one land animal which have unihemispheric sleep.
Social organization
Bottlenose dolphins live in groups called “pod”. A pod is a stable, long-standing, independent community. Pod composition may change. It is composed of groups – elementary units. Pod size and structure depend on members’ age, sex and reproductive conditions. Family groups are formed by females and their brood of different ages. Juveniles of both sexes and different ages join in with females and calves.
Juveniles are observed generally both in same-sex and different-sex groups. Adult males rarely make community with male-juveniles, usually they live alone or in pairs. They move around female groups and may make short-lasting pairs with females.
The deeper and opener the space of living, the larger pod’s size is. Big pod affords better protection and hunting. Pods may join together for a short time (for several minutes or hours) forming large groups called “flocks”. Sometimes such flock numbers in hundreds.
Pod is a stable social unit providing optimal conditions for protection and hunt. It appears that pod’s stability is based mostly on family relations.
Relationship
Social hierarchy exists more or less within bottlenose groups. During breeding season, when males groups join together with females groups, hierarchy within such communities is established. Adult males hit on young ones which try to pay attention to adult females. Scars on dolphins’ skin prove hierarchal relations within groups.
Adult males in captivity establish hierarchy by threads and fighting. Aggression degree depends on age and sex of group members. Sometimes adult males demonstrate aggression not only toward young males, but sometimes and toward females with calves. Usually there are no violent fights within groups of one male and several females. Males lives together rather peacefully. But keeping males and females of different ages in the same pool may provoke fights and strives. The strongest male dominates in mixed groups. And sometimes leading position belongs to old females.
Hierarchal order is essential for conflict prevention.
Behavior
Daily behavior of dolphins is diverse. Duties of adult males include pod’s periphery control and protection. There are also dolphins which explore new objects and territories and “report” to the pod. Bottlenose dolphins are active hunters, but they hunt mostly in the morning or night.
Play behavior of dolphins is also diverse. They play and ride on the bow waves or the stern waves of boats, leap above water, sometimes vertically, twirling and plapping alone and in groups.
Frequently it may be observed that dolphins play by jellyfish and fish, throwing and catching them. Both young and old dolphins chase each other and play “tag”.
Interraction with other species
Bottlenose dolphins have been seen with groups of other dolphins, such as pilot whales, spinning dolphins, spotted and rough-toothed dolphins.
They ride the waves of large whales, chase white-bellied dolphins from prime spots on bow-waves.
Dolphins respond to sharks sometimes with aggression, sometimes avoidance. Tiger sharks elicit the strongest responses. Researchers have observed dolphins attacking, and sometimes killing sharks.
Some dolphins in the wild like to attract frequent attention of people on the beaches.
Diet and eating habits
Dolphins are active predators and eat a wide variety of fishes and crustaceans. The foods of dolphin vary with its geographic location. Adult bottlenose dolphins eat approximately 4% to 6% of their body weight. A nursing mother's intake is considerably higher: about 8%.
Dolphins do not chew their food. Usually they swallow the fish in whole, head first to reduce a possibility of throat injures from sharp spines. They also pull to pieces large fish.
Hunting
Hunting strategies are diverse. Pray is chased as well as by the whole pod, and also by separate group or scouting dolphins. In open waters dolphins encircle a large school of fish and herd it into a small, dense mass. Fish starts moving in a circle. The dolphins take turns charging through the school to feed.
When hunting close to the shore, dolphins herd schools of fish to the coast, block them and easily trap in shallow water.
Bottlenose dolphins may also hunt alone, especially on large fish. A dolphin stuns the fish by its fluke or throws it above the water, and then retrieves back.
Reproduction
Bottlenose dolphins become sexually mature at various ages. Usually females became mature between 5 and 12 years with body length about 2,3 m. Males become sexually mature at age 10 to 12 years with body length 2,4-2,6 m.
Females are fertile for most of the year. Bottlenose dolphins in the Black Sea may breed throughout the year, but usually calving falls on summer.
Courtship of dolphins is typically consists of certain phases: chasing of each other at high speed, cross-swimming, demonstration of bellies to each other, stroking of each other by rostrums and fins, leaping out of water, head-butting, copulation.
Usually a male chooses a female and shows affection during several days or even weeks. Males chafe against female, cuddle, slightly bite, demonstrate S-pose lifting the head and turning tail down. The dolphins copulate in motion.
Gestation period is about a year. Female dolphins can potentially bear a calf every two years, but calving intervals generally average three years. The most intensive fetal growth is at the last two months of gestation. Deliveries duration is usually from 15 minutes to 2 hours. Baby-dolphin is usually born tail-first. The umbilical cord snaps during delivery.
Very often an assisting dolphin presents at birth. Although these assisting dolphins are called an "auntie" dolphin, it may be male or female. They surround mother and protect her baby. Calves are 100-105 sm long and weight abour13-15 kg. A new-born slowly swims to the water surface to inhale for the first time.
The absence of pelvis and hind limbs allows big calves to be born. Usually calf’s mass is 10-15% of mother’s body mass.
In the first few days after birth, the calf's dorsal fin and tail flukes are flexible and soft. Dorsal fin lays on the back, fluke is in a roll. But gradually fins uncurl and stiffen.
Calves are darker than adults. As a result of fetal folding they have light lines on their sides. The lines disappear within six months.
Care of offspring
Nursing usually begins within 6 hours of birth. Calves nurse under water, at shallow depths. Nipples are hidden inside of slits on mother’s belly. A calf grasps mammary gland with its beak. He can’t suckle as has no lips, thus, mother squirts milk into calf’s mouth.
As each nursing usually takes about 5 to 10 seconds, a calf nurses 3 to 8 times per hour throughout the day. Later intervals increase.
Milk is composed of 33% fat, 6.8% protein, and 58% water, with traces of lactose. The rich milk helps the baby rapidly develop a thick blubber layer.
A mother dolphin stays close to a calf and looks after him. The calf follows mother in her stern-wave. Two-week-old calf attempts to swim away from mother for a short time, but in case of any danger, he rushes to mother and calls her. During the first month mother keeps a calf in sight and if an adult dolphin approaches, always stays close to baby. But at 12-month age a baby-dolphins frequently swim alone joining to other dolphins.
Calves grow very fast and achieve 1,8 m length by 6-month age. They begin to take fish at age about 6 months (hen the teeth begin to erupt). At the age of 9 months 50% of calf’s feed is mother’s milk and 50% is fish. A calf may nurse up 18-month age.
A mother actively teaches baby-dolphin and prepare for adult life.
Longevity
According to the studies in the Black Sea dolphins live 30 years or less. Observations in oceanariums show an average age up to 48 years. The most exact age can by esteemed by examining annual growth of tooth layers. Annually a new layer of dental material covers dolphins’ teeth. Number of such layers allows esteeming animal’s age.
Age can be estimated by examining a sliced section of a tooth and counting these layers.
Predators
Dolphins’ remains are frequently found in large sharks’ stomachs. Killer whales may occasionally prey on bottlenose dolphins.
Human impact
In the past dolphins have been taken directly for meat, leather, oil, and meal for farms. Dolphins are affected by environment pollution and habitat destruction.
The population of the Black Sea bottlenose dolphins is obviously reduces by a number of adverse factors: reduction of nutritive base, navigation traffic increase, water pollutions, fisher activity. Dolphins entangle in fishing nets and injure or even die.
Conservation
The Black Sea bottlenose dolphins are threatened species Red-listed both in Russia and in Ukraine.
Due to reduction of the Black Sea dolphins their fishery has been forbidden in USSR, Bulgaria, Rumania since 1966, in Turkey since 1983.
Copyright belongs to N.D. Grechishkina. Any use of the text is only with consent of the author.
