? 發問於 科學及數學生物學 · 1 十年 前

all about dophin...........

Please help me to answer the questions below:(about 20~40words each questions)

1)Describe its external features.

2)What does it eat .How does it eat?

3)How dies it move?or How dies it respond ti stimuli?

Thanks a lot!!!

1 個解答

評分
  • Gemini
    Lv 4
    1 十年 前
    最佳解答

    Both Dolphins and Porpoises belong to the suborder Odontoceti. Members of this order possess teeth, a single blowhole, and sometimes exhibit sexual dimorphism. Odontocetes also possess bilaterally asymmetrical skulls that often support a well developed bulbous forehead.

    Most odontocetes are more social than other groups of cetaceans and use echolocation for navigation. Echolocation is the use of sound waves bounced off on objects. It is also used to locate shoals of fish for food.

    These similarities often lead to a misconception about the dolphins and the porpoises. Although the terms 'dolphin' and 'porpoise' are often used interchangeably, they describe two different groups of cetaceans.

    Dolphins belong to the Family Delphinidae, while porpoises belong to the Family Phocoenidae. Many external characteristics that are useful in distinguishing these two families exist. For example, the extended beak present in most dolphins is absent in most porpoises.

    All dolphins and porpoises have a melon.

    Some members of both families lack dorsal fins altogether. The teeth of dolphins and porpoises are distinct from one another. Dolphins possess homodont conical teeth in their jaws.

    Some dolphins have teeth in only one jaw whilst others have teeth in both jaws. Porpoises posses spatulate, or spade-shaped, teeth in both jaws. Homodont is where the species has one type of teeth. Humans have four types of teeth and are hetrodont.

    Large schools of finless porpoises have been observed but they are porpoises which are seen in groups of one or two individuals. Dolphins move about in sizeable groups. Dolphins can often be seen performing acrobatics, such as breaching, or leaping out of the water and returning with a splash.

    Similarly, many dolphins can be observed bow-riding, riding on the pressure wave of a large ship or whale. Unlike dolphins, porpoises are rarely seen bow-riding.

    Dolphins can live to about 40 years. The skin of the dolphins looks smooth but they have tiny ridges to allow the water to flow off and allow them to swim swiftly through the water. They have strong tail muscles that assist in their movements in water. They are graceful social animals.

    Many dolphins rely on speed, agility and cooperation within well- organized hunting packs to catch their prey.

    Observation of spinner dolphins off Muscat island feeding on tight balls of schooling sardines, showed the dolphins to be swimming through the school in sequential droves of three to four individuals, each seizing a mouthful of fish. Other dolphins circled around, herding the fish together, and awaiting their turn to feed.

    Fishermen now, due to an increasing market for their flesh, catch dolphins and porpoises. Anouk Ilangakoon, says "Basically the dolphin harpoon fishery has come about in the last 20 years. With dolphins getting caught in the gillnets, people started consuming dolphins-therefore the market grew".

    Now that there is a market andfishermen in certain areas have resorted to this direct harpooning technique of taking dolphins. It happens only in some areas in the country, mainly on the south coast but has spread to areas on the west coast as well.

    However, within the past ten years or so, this practice has spread further. Dolphin flesh is cheaper than the more popular kinds of fish.

    It is necessary that an awareness is created amongst the people, especially those consuming their meat, and the threats to their populations highlighted.

    This awareness will enable them to have a better understanding of the species. This would create public concern within the country and this concern would go a long way towards the conservation of these marine mammals.

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