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Sea Mammals

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Bottle-Nosed Dolphin

Bottle-Nosed Dolphin

ORDER: Cetecea, SUBORDER: Odontoceti (toothed whales),
FAMILY: Delphinidae
They live in cold temperate to tropical seas.
They have streamlined body, ideally adapted to fast movement through water due to its externally smooth and hairless skin.
They are 2.3 - 3.8m in length and weight about 150 - 300kgr. Unlike other mammals, they have only one nostril, the blowhole, which is located on the top of their head and from which they breathe.
They spend almost all their lives under water, but they have to surface to breathe (they can't get oxygen from the water).

 

Like all mammals, dolphins are warm blooded. In order to maintain their temperature at 36 - 37°C in the aquatic environment they have a layer of fat known as blubber. They also have a controlled blood flow from body core to the skin, which minimizes heat loss and furthermore they reduce their heartbeat at 12 beats per min. The fin, flippers and flukes help dissipate body heat when needed.
Unlike fish they propel themselves by vertical strokes of their tail and they use their fin for stabilization and their forelimbs for steering.
Life span is 25 - 50 years.

 

STATUS
Abundant and widely distributed but some regional and local populations are at risk of disappearing because of:  Habitat degradation, fishery conflicts, pollution, killing (for food or bait in some areas), viral outbreaks, acute exposure to toxins, accidental capture in fishing nets and collisions with boats.
Their natural enemies are sharks.
In Greece a 1972 decree put a “bounty” on dolphins. This decree was repealed in 1982. Today most dolphin species are protected and  their  killing is forbidden in all EU countries, as well as in many other countries of the world. The subspecies ponticus is endangered.


Senses:
Their eyes are perfectly adapted for seeing well in and out of the water. They have a highly developed sense of hearing and they communicate with each other with a wide variety of sounds.
Dolphin's strongest sense is echolocation. They produce echolocatory clicks which bounce off objects in their path, producing echoes from which the animal can build up a complete sound “picture” of its surroundings. Echolocation helps dolphins to locate their prey, their predators and to navigate. Their sounds range from 0,2kHz to ultrasonic range around 80 - 160kHz. The echolocatory clicks are produced in the nasal sac region and not by the larynx.
They have no sense of smell. They have very sensitive sense of taste, higher than humans.

 

Social behaviour:
Very social animals. Depending on the habitat they are found in groups of 2 - 15 individuals although groups of more than 1000 have been reported, as well as lonely male individuals.
The basic structure of the groups is:
- mothers with their calves and possibly males
- juveniles in mixed-gender groups forming temporary relationships,
- adult males, as individuals or in pairs or trios with strong bonds.
Dolphins can be aggressive in order to maintain hierarchy.

 

Reproduction:
Dolphins mate, give birth, suckle and nurture their calves in water. 
They breed throughout the year but mostly in warmer months.
They are polygamous.
Females are sexually mature at the age of 7 - 12, males at 10 - 13.
Gestation period lasts about 12 months.
The calf is usually born with his fluke first.
Newborn calves are about 1m in length and weight 11 - 12kg. 
The lactation period lasts up to 2 years. At the age of 4 months, the calf might also eat fish along with milk.
They stay with their mother for 3 - 6 years, after which the mother is ready to mate again.

 

Amazing facts!
Dolphins are highly intelligent and have mimetical skills. Compared to humans, their brain has double and more complicated coils and more neurons. They never sleep! During the night, left and right side of their brain rest in turns, allowing the animal to remain 'conscious' in order to surface to breathe and carry on basic survival behaviors. They leap up to 5m high in order to herd fish, for sexual display or just for fun. They reach up to 45km/h in swimming speed. They can dive up to 300m deep and can remain under water for about 15min. When one member of the group is sick or injured, two other dolphins uphold it to the surface until it recovers. Dolphins help with great success in the therapy of people with psychological problems and development disorders.
The largest member of the delphinidaie family is the Orca.

 

Dolphins in mythology
Dolphins were known from the ancient times and are often referenced in Greek mythology.
God Apollo, after fighting with the dragon Python, created the temple of Delphi. Then he transformed himself into a pod of dolphins and helped a lost ship. The astonished sailors sworn to serve the temple of Apollo and later renamed it to Delphi in honor of the form he had taken.
The ship of Ulysses had a dolphin as an emblem, out of gratitude for the rescue of his son Tilemachos by a dolphin. 

Dolphins adorned many ancient coins and pots and the Knossos palace was decorated with dolphin images.
In the story of Arionas the Lyrodos, Herodotos writes that one day, when Arionas was returning from a trip, the crew threatened to drop him in the sea to take his money. He asked to play his harp as a last wish. A pod of dolphins enchanted by his music, saved him and carried him to land on their back.
God Dionyssos transformed the pirates that attacked him into dolphins and assigned them to save sailors in danger.
Dolphins were carrying Dionyssos to and from the underworld.
They always accompanied Poseidon, the god of sea, when travelling with his golden chariot over the waves.




Harbor seal

Harbor seal

They live in coastal waters but also found in bays, rivers and estuaries. They go ashore to breed, rest and moult. They are solitary in water, but on land they form large colonies.

 

Unlike dolphins, seals exhale before diving. They can stay underwater for approx.10min and reach depths of 150m or more.

 

Adult males can reach up to 1.9m long and ~150kg, females 1.7m and ~110kg. Males mate with one or a few females during a season. Gestation lasts ~11 months. Females nurse their pup for only 3 - 4 weeks. Pups are able to swim and dive within minutes from birth and often ride on their mother's back while in water. Lifespan is typically 35 years for females and 25 years for males.

 

• Good vision in and out of the water, probably colourblind.
• Ηighly developed sense of smell only outside water. Females use smell for pup recognition, and males to locate females in oestrus.
• Seals have no external ears. Instead they have a meatus behind their eyes, with a keen sense of hearing. Τhey locate the origin of sounds very precisely by making scanning movements with their head.
• Multiple layers of blubber provide insulation, buoyancy and energy reserves.
• Short and thick fur with patterns unique to each individual, like the human fingerprints. Glands in the skin secrete oils that protect the coat.
• For hydrodynamic reasons no part of their body protrudes, not even their genitals which are hidden in a skin fold!
• Their flippers are very short, covered with hair and have claws as long as 5cm. They are adjusted for swimming, but not walking.

 

Status in the wild: Stable population in the wild estimated at ~500,000. Main threats are entanglement in fishing nets, overfishing, illegal hunting and licensed killing to protect fisheries (allowed in the UK, Canada and USA), viral outbreaks, oil spills and chemical pollution. Their natural enemies are large sharks, killer whales, walrus, gulls and ravens, feral dogs and eagles.