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Sea Mammals

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Bottle-Nosed Dolphin

Bottle-Nosed Dolphin

Habitat: primarily coastal, but they can also be found in pelagic waters

 

Gestation: Dolphins mate, give birth, suckle and nurture their calves in water.  Gestation lasts ~12 months.  The calf is usually born with his fluke first.  Newborn calves are about 1m in length and weigh 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.

 

Social structure: typically groups of 2-25 individuals, although groups >1000 individuals have been reported, as well as lonely male individuals. They maintain hierarchies.  Polygamous.

 

Weight: 650 kg max

 

Dimensions: 4.1m max

 

Lifespan: 25-35 years

 

IUCN Status: Least concern

 

Estimated population in the wild: ~600,000

 

Threats: 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.

 

Did you know that:

  1. They have streamlined body, ideally adapted to fast movement through water due to its externally smooth and hairless skin.
  2. Unlike other mammals, they have only one nostril, the blowhole, located on top of their head and from which they breathe.  They spend almost all their lives under water, but they have to surface to breathe.
  3. Like all mammals, dolphins are warm blooded. In order to maintain their temperature at 36 - 37°C 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. 
  4. Unlike fish they propel themselves by vertical strokes of their tail and use their fin for stabilization and their forelimbs for steering.
  5. 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.
  6. 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.
  7. They have no sense of smell.  They have very sensitive sense of taste, higher than humans.
  8. They never sleep! During the night, the 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 behaviours.
  9. They leap up to 5m high in order to herd fish, for sexual display or just for fun. They reach up to 30km/h in swimming speed.  They can dive up to 250m deep and can remain underwater for 8- 15min.
  10. When one member of the group is sick or injured, two other dolphins uphold it to the surface until it recovers.
  11. The largest member of the Delphinidae 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

Habitat: Coastal waters, bays, rivers, estuaries. They go ashore to breed, rest and molt.

 

Gestation: ~11 months. Mothers nurse their young for only about 3-4 weeks, 1 pup

 

Social structure: Solitary in water but form large groups when ashore. Polygynous (males mate with one or a few females)

 

Weight: Males reach 150 kg, Females reach 110 kg

 

Dimensions: Males reach 1.9m, Females reach 1.7m

 

Lifespan: 30  - 35 years. Females typically live mone than males.

 

IUCN Status: Least concern

 

Estimated population in the wild: 610,000 - 640,000

 

Threats: 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.

 

Did you know that:

  1. Unlike dolphins, seals exhale before diving. They can stay underwater for ~ 10min and reach depths of 150m or more.
  2. Pups are able to swim and dive within minutes from birth and often ride on their mother's back while in water.
  3. Good vision in and out of the water, probably colorblind.
  4. They have a highly developed sense of smell only outside water. Females use smell for pup recognition and males to locate females in oestrus.
  5. 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.
  6. Multiple layers of blubber provide insulation, buoyancy and energy reserves.
  7. Short and thick fur with patterns unique to each individual, like the human fingerprints. Glands in the skin secrete oils that protect the coat.
  8. For hydrodynamic reasons no part of their body protrudes, not even their genitals which are hidden in a skin fold!
  9. Their flippers are very short, covered with hair and have claws as long as 5cm. They are adjusted for swimming, but not walking.
  10.