The Manta Ray
in Puerto Vallarta
By Griffin Page
Naturalist ~ Eco-guide
For many divers and snorkelers, Manta rays (Manta birostris),
also commonly called devilfish, giant mantas and in Spanish
manta rayas, are a most sought out species. Their angel like
flight under water is a most spectacular sight. So graceful
and agile are these creatures that they often offer us a show
resembling a classical ballet performance almost equal to
those I’ve seen on big production stages. Their leaps
out of the water are also quite impressive….up to 7
feet! Why they do this? Many hypotheses have been brought
forth but very little is actually know about why they jump
clear out of the water the way they do. Some say it’s
perhaps to clean themselves of parasites and shed some dead
skin, or to play, perhaps some kind of fishing technique and
I even heard someone say they do it to help push a newborn
out of their womb. Wow! I think I’ll wait for a more
complete scientific study to form my own opinion.
Until recently, manta rays were divided
into different species (Manta alfredi, M. ehrenbergi, M. hamiltoni,
M. birostris) based on coloration differences, size variation,
and geographical location. However, investigations by scientists
such as Tim Clark from the University of Hawaii show that
manta rays are all one species, Manta birostris. Tim plans
to publish a comparison of genetic samples from several worldwide
populations to establish this hypothesis.
rays have a generally triangular body plan. The pectoral fins
have evolved into wide triangular wings with which the head
has fused and giving the manta a broad blanket-like body,
thus earning them the name 'manta', the Spanish name for cloak.
This wonderful species is related to the shark family. Sharks,
unlike fish (which have a bony skeleton), have a body structure
made completely of cartilage, allowing them more flexibility
of motion. Their coloring may vary from black, blue grey or
dark brown dorsally and generally have a white underside,
sometimes with varying darker patterns.
Each Manta ray has a unique color pattern. Both the dorsal
and ventral color characteristics are used to identify individuals.
They may attain a disk width of 29 feet (9 meters) maximum
but will usually average more like 22 feet (6.7 meters) at
full growth. They can attain a weight of 3000 pounds (1350
kilograms) and their life expectancy is estimated at around
20 years although not yet confirmed. They can also dive to
depths over 720 ft, sail several yards out of the water, and
reach speeds of over 14 miles/hour.
underwater giants inhabit temperate and sub-tropical waters
around the globe (between latitudes 35° N and 35°
S). They tend to travel a lot, mainly in the search of plankton
rich areas. They are filter eaters, as are most Mobulids (which
means it belongs to the family of Mobulidae). They feed on
microscopic organisms such as copepods, mysids (minuscule
shrimp-like animals) along with larvae of fish, lobster, and
octopus that float and swim in the open water. Some have been
seen looping vertically for extended periods while feeding.
They will eat about 2% of their body weight daily. This represents
56 pounds for an adult weighing 2800 lbs!
is little sexual dimorphism between males and females. Males
are distinguished from females by the presence of two claspers
(male sex organs) located adjacent to the inside edge of each
pelvic fin. Females will reach sexual maturity when their
wingspan has reached 11 feet and it is estimated that it will
take them approximately 5 years to reach it. Reproduction
will usually take place near rocky reefs and many males can
be seen courting one female. In order to mate, the male will
bite the pectoral fin of the female before placing himself
in a belly to belly position. He will then insert one clasper
into the cloaca (cavity where intestinal, urinal, and reproductive
canals come together) of the female. Gestation is believed
to take 13 months Manta with Remoras. Photo by: Steve Jones
but the exact time is unknown. Mantas reproduce via aplacental
(without a placenta) viviparity (give live birth). A pup hatches
from its thin-shelled egg inside the mother. After hatching
the pups are fed by uterine milk until they are ready to be
expelled. Females give live birth to one or perhaps up to
two pups that are about 3-4 feet (1-1.5 meters) wide and weigh
approximately 20 pounds. The pectoral fins are curled around
the pup in an S-shape when inside the mother. When the pups
are expelled they unfold their wings and start to swim. Young
mantas grow very rapidly and are thought to double their size
in the first year!
rays were once commercially harvested from Australian and
Californian waters for their liver oil and their skin which
was used as an abrasive and durable leather goods such as
wallets. Although it is now rarely hunted, Manta meat is still
a delicacy in the Philippines and I have seen it served here
in our bay on a few occasions, mostly, at beach side restaurants
of very small towns. It is still actually fished in certain
areas of the world including La Paz in Baja Califirnia Sur.
As a matter of fact, the IUCN classifies this species as DD
(Data Deficient) and their report is as quoted here: “This
common and widespread large coastal plankton-feeding ray is
very widely distributed in tropical shelf waters and around
oceanic islands. The species is highly Manta ray fishery.
Photo by Jonathan Roldan vulnerable due to its life history,
giving birth to just one very large pup every two or three
years. There are no target fisheries in most parts of its
range, and by-catch is rare under the present fishing methods
in use world-wide. Unfished subpopulations are not considered
threatened. However, wherever there are fisheries the species
quickly becomes vulnerable, population declines have been
observed where target fishing has taken place, and there is
a commercial market for them in various places of the world.
Reportedly, they are now very scarce in the Gulf of California.
Populations will rapidly decline unless the fisheries are
carefully managed. More data on population status is required
to assess the species' conservation status.”
Dive tourism has benefited greatly from the
manta in locations where they are reliably encountered and
sometimes approach divers. In these areas, where divers often
touch and interact with mantas, the rays can develop skin
lesions in response to the removal of the thin protective
mucous layer. Let’s dive consciously!
could be such a wonderful teacher if only we saw it for what
it really is” ~ Monachí