biology of Manta Ray Final

This topic submitted by Ben Schooler ( Schoolbo@muohio.edu) at 10:19 PM on 8/12/08.

The Alien Song--Interesting! (Quicktime movie)

Tropical Field Courses -Western Program-Miami University

Ben Schooler
06/07/08
Professor Cummins

Biology of Manta Rays

Large, majestic creatures gracefully floating through the warm temperate waters like angels of the ocean. Manta Rays are some of the largest creatures in the ocean these ÒflyingÓ animals are known for their docile behavior and eerie presence. In earlier years people believed the Manta Ray to be a sea creature related to the devil because the body of the Manta Ray appears with two wings and a frontal mouth piece which looks like two horns protruding from the body of the ray. The creatures are actually very tame and beautiful, but are starting to disappear from their natural habitats.
The Manta RayÕs scientific name is Manta birostris. The Manta Ray is the largest known species of ray in the ocean, and are believed to possess a lifecycle of around 22 years. Its wing span has been accurately measured up to 6.7 meters, but they have been known to have a wingspan of 9.1 meters! Even though they can grow to be great widths, it is very common to have a wing width of 4 meters. As one looks at the particulars of the ray, you can see how there are different patch and spot patterns on the rays. Each pattern is unique on all rays. This makes it easier for researchers to identify the different rays which they come across especially if they are trying to find a different ray each time. Another particular about the patterns and colors on the rays is that they are different from region to region in which they are found. For example, Manta Rays which are found in the eastern pacific region are known to have a ÒduskyÓ to a almost black pattern on their undersides, while rays in the western pacific region are known to have an almost completely white underbelly. I have known come across any information as to why they are colored differently in the different regions.
Mantas are not considered hunters because their diet pretty much contains just plankton, which require the mantas to be filter feeders like the whale shark. What the ray will do is use its head fins (cephalic fins) to funnel the plankton into the mouth (when people look at these fins on the ray, they tend to look like horns protruding from the head of the manta ray which is how it got its nickname the ÒdevilÓ ray) and these Ògill rakersÓ filter the plankton into the mouth so that the ray can digest its incoming food (marinebio.org).
Another misconception which people may look at and assume about the manta ray is that these types of rays do not contain stingers or venom of any kind on its body. Even though these giant creatures seem to share the same features as there look-a-like cousins the sting ray, the manta rayÕs only means of defense is its giant wings which they could use to ÒbeatÓ an unfriendly creature over the head with. Although according to Yapese myth, the manta rays have the ability to grab a person with its wings and squeeze them to death (marinebio.org), this of course is untrue, but you can see why people might have been afraid of these creatures. Since the Manta ray really does not have any real predators except warm water sharks such as the tiger shark (elasmo-research.org), there really is no mean for them to have a venomous defense mechanism.
An interesting fact about the Manta Ray which some people do not realize is even though they are related to the sting ray family, Manta Rays do not possess a stinger at the end of their tail ÒwhipÓ, but they do have a small dorsal fin at the end of their bodies which connects to the whip of the ray. When looking at the Manta Ray some people think that these rays do not possess teeth, this is entirely untrue. Manta Rays have about 300 rows of little peg-like teeth. These teeth are about the size of a pin head. The ray also has very similar scales inside the mouth called denticles (Shark Research Institute, www.elasmo-research.org). These scales are not meant for feeding even though they are almost undistinguishable from the regular feeding teeth. One theory about the use of the denticles is that they are used for mating purposes in the rayÕs courtship/reproduction since to ÒgrabÓ a mate, the male must use his teeth/denticles to grab onto her before he can fertilize the female.
Since we are now on the topic of reproduction for the manta rayÕs, we will look into the courtship and conceiving of a ray. As I had mentioned before, the male ray must use his teeth to attach himself to the female before he can fertilize her eggs. The rays reproduce internally so when the male has ÒcaughtÓ a female (after much chasing after I might add) the male uses a penis like organ called a clasper (which each male has two of) and inserts it into the vent of the female. This entire process lasts about 90 seconds. The amount of time it takes for a new born ray to be born (called ÒpupsÓ) is not accurately known, but is speculated to be around 9 to 12 months and possibly more. Usually when a female produces a litter of pups, there are no more than two of them for that particular litter. After a female gives birth, she usually waits at least a year before she tries to mother another litter. Even though we know some about the courtship and mating of Manta Rays, little is know about there birthing takes place (whether they return to a special area or if there selection is based on appropriate habitat), also newborn manta rays are rarely reported since it is quite difficult to find a ray as it is given birth. Typically the newborn pups are about four feet across (1.2 meters) (elasmo-research.org).
The manta rayÕs habitat is somewhat scattered throughout the globe. Usually rays like to settle in the nearshore waters (like continental and insular shelves) (Reproduction and Life history, www.elasmo-research.org). They also like to be near coral reefs and rock reefs and donÕt mind going out into the deeper waters (mantas have been seen diving at 100ft deep, but there actual range is unknown). If you see a ray you are more likely to encounter it swimming near the surface and some rays have even been seen flying out of the water like jumping dolphins through the air. The juveniles are the ones who tend to fly out of the air the highest since they can gain the most speed and are the lightest. Most of the time these rays will do two or three successive jumps in the air for no particular reason. Scientists are not particularly sure why the rays fly out of the waters, but some speculate it could be a form of body language to communicate with other rays.
Overall these mysterious creatures are probably some of the most beautiful animals in the sea. People who are hunting them for there meat are only wasting away a beautiful animal because a manta rayÕs meat only goes for around .40 cents per pound on the Asian market while the sharkÕs dorsal fin can go for 30$. It is a waste of both species to be exploiting such a graceful creature. Even though manta rays are not on the endangered species list, it doesnÕt mean we have to hunt them until we put them there. These rays have so much to offer since we really donÕt know a whole lot about their lifestyles and we could learn so much more from them. Their past was cloaked by myths and fear and we are finally getting the chance to understand and see these beautiful creatures better!

Sources:

marinebio.org

http://www.elasmo-research.org/education/topics/lh_manta_faq.htm

http://www.elasmo-research.org/education/topics/lh_manta.htm

www.mantapacific.org

www.freedive.net

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