STING RAY’S LIFE
Stingray came into being during the same age as dinosaur (approximately more
than 150 million years ago). They are younger brothers of shark, which has
come to being for more than 200 million years ago.
It is believed that evolution chain has started from shark to shovelnose ray
to skate (rays that still has tail like shark) to sting-rays to eagle rays
and to manta.
At present there are more than 450 types of rays from the palm size to several
meters size like manta.
Ray’s tail has reduced in shape and does not assist swimming. Ray’s gill is
under the body.
Ray’s eyes are on top or at the side of the body (for manta). They cannot
see underneath. Rays use nostril to smell, lateral line and sensing electrical
waves from other animals.
Ray’s mouth is mainly underneath, including eagle rays. For manta and devil
ray, mouth is in front.
Movement of manta
Manta moves forward
with wings like birds flying. When flapping the wings up and down, there will
be propelling force. But manta does not have tail feathers like birds. So,
uneven flapping of each wing is used to steer left or right. Birds cannot
do this. However, manta cannot swim backward.
Food of most rays, including eagle rays, is small seabed crustaceans. Teeth
are votaline type. But manta eats plankton. So, the teeth have reduced to
almost vanish.
Mainly manta search for food in the middle of the water. Some time they might
search for food near the seabed, flapping the wings to disperse sediment and
open their mouth to eat. (I witnessed this.)
Manta might search for food at night. They would go near the boat with lamps
to lure squids or small fish, eating plankton and small fish lured in by the
lamp. (I witnessed this as well.) Diving spot famous for spotting manta at
night is the Hawaiian Islands. A special trip can be arranged.
Rays’ defense mechanism is venomous spine. There are two venomous glands in
the tail. When skin is torn, the poison will be injected to the wound. The
poison has a composition of protein. When poisoned, use warm water bathe or
hot water bottle to treat the wounds.
Most type of rays including several types of eagle ray has spine Manta and
devil ray do not.
electric rays can emit more than 200 volts current. There is a report that
this group of rays has been found in Thailand. But there has not been any
news about people being harmed.
Ray is the cleverest animal among cartilaginous fish group (including sharks).
The brain to body weight ratio is similar to birds and marsupials. Among these,
manta is considered the cleverest.
Rays mate internally. The male has special organ called clasper that has been
developed from pelvic fins, used to clutch and inject sperm to the female.
Some types of rays mate in front to back position. Some types mate in front
to front position.
For manta, there is a report that divers (in other country) met manta mating
near the islands. There was a female and several males taking turn mating.
The female was swimming with her front upward, whereas the males swam down
in a front to front position. Other males were floating near the water level.
This data are still not confirmed.
Only skate group spawns. Most rays including manta deliver cubs. (The ovum
is hatched in the ovary.)
Rays’ roe and cubs a little comparing with other fish, some time only two
or three. If we caught too many of them, the probability of extinction is
very high.
Rays’ embryo is not in plankton form like other fish. It grows in the ovum
or in mother’s ovary before hatched, in order to gain a better surviving chance.
Dissemination of rays depends on habitat of the mothers, since young rays
are not in plankton form which can float along the water like other fish.
Nowadays, the study about rays in Thailand hardly exists. At the same time
we make use of rays like grilling, making fish dumpling, making animal fodder,
making imitated shark fin etc. until extinction is concerned.
In some countries, especially in the middle and south pacific islands, natives
may catch manta by harpoon or special tool.
In Thailand no one specially kills manta for food. But many times manta ray
was unlucky enough to be caught to death in drift net or rounded net.
Overseas, there is not so much study about manta because of expense involved.
If further information is required, look in the web site called www.on-the-edge.com.
There is an information about world spreading as well as other information.
Study about rays, especially their behavior in order to find the way for them
to exist...This is what Thai people need, if we want our sea to accommodate
them for our future generation to use.
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