Manta Ray Threats
In the past
mainly fished by local fishers of small communities, for the purpose of:
- using the oil from their livers for water proofing
their skin for making small percussion instruments
their meat for food, where food sources were scarce
as they are not considered to taste good.
that time they
used artisanal techniques, fishing with harpoons in small wooden boats
by paddles and sails made form palm fronts. However,
days manta ray fisheries are overfished worldwide using big motor boats
efficient catching techniques such as trawling, nets and radars. The
reason for this is that the cartilagenous structure protecting their
in high demand in China as traditional Chinese medicine - which is said
everything ranging from diabetes to a common cold however their is no
to proof this. The consequence of this is that fisheries that in the
not target manta rays and only caught them in the by-catch, are now
them for their gills which have a high value on chinese
markets. While initailly a few hundred mantas were caught by artisanal
fisheries, now thousands (primarily M.
birostris) are caught each year. The main countries that take
part are the Philippines,
Indonesia, Tonga, India,
Lanka, Brazil, Peru, Madagascar,
Mozambique, Somalia, Ghana and Tanzania but also
American and European
countries used to join the hunt for the “Giant Devil Rays”.
traditional to comercial fishing generally results in a collapse of the
In Mexico (Sea of
Cortez), the manta ray
fishery became commercial in the 1980s and in 2007 the fishery
similar story occured in the Phillipines and now that population is
fisheries, by-catch is another big problem causing the incidental
mantas in drum-line, shark-nets (used to protect the beaches against
however most sharks are found on the inside of the nets, meaning the
caught on its´way out to sea), and comercial nets for other target
2) Habitat Destruction
is a huge problem for most marine life at the moment. The coral reefs,
manta rays come to feed, reproduce and clean at cleaning stations, are
3) Marine Debris
as oil spills, plastics and microplastics cause serious damage to manta
they are filter feeders. This means that they filter plankton and with
they intake various forms of pollution which causes internal injuries,
GEAR (ghost nets, fishing lines, moorings): cause
entanglement of the head and
cephalic fins of the manta rays which results in:
cephalic fins or amputations of other parts of
the body impairing their ability to feed.
as mantas cannot swim backwards and they must
swim constantly to flush oxygen-rich water over their gills. So in a
cases they died from drowning.
plankton as their primary food source. Changing sea temperatures
phytoplankton’s natural ecological cycles and change the plankton
So they struggle to find adequate food supplies. This forces them to
their migratory patterns frequently.
5) Marine Traffic
is greatly on the increases where manta rays are present. This results
frequent boat strikes, collisions and entanglement with anchor lines.
these are generally fatal.
6) Unregulated Tourism
aggregations of mantas have become tourist attractions resulting in the
presence of many boats in places where mantas are easy to observe and
large volume of snorkelers and divers in the water close to the mantas
touching them. This causes great stress to the animals, disrupting
feeding, reproduction of cleaning patterns.
few mobula rays live in captivity, the unmonitored
removal from the wild for the public aquarium trade may have negative
on small and geographically isolated populations.
8) Natural Predation
predators of manta rays are: sharks, orcas and false killer whales. In
most of the
cases non-fatal injuries have been seen, especially with shark bites,
but we do
not know how these injuries affect the long term survival of mantas or
these threats, are not a species which can be fished in a sustainable
they have a:
reproduction rates due to their: late maturity, long
gestation periods and give birth to only one pup every one to two years
these threats but especially overfishing and their biological history
to a dramatic reduction in their populations worldwide. Both Manta birostris and Manta
alfredi are now listed as VULNERABLE in the Red List of
Threatened Species (ICUN). However in spite of this, mantas remain
in most part of the world (including Australia).Only in the places
collapse in the fishery was declared, such as in the Phillipines and in
(sea of Cortez), are the species protected.
Data is missing about
A lot of
information essential to the protection of manta rays and their
missing including: data about their biology, ecology and behavior.
Manta Ray Conservation
tourisms generates far more income than manta fisheries. It is
50 million USD are generated by tourism each year while only 250-500
paid for a manta at an Asian market. In the Phillipines a large manta
less than 100 USD to a fisherman but generates 8 million USD a year in
(Ray of Hope).
Eco-tourism with sustainable diving practices and proper codes of
boat approaches as well as educational material is important for the
of manta rays. Along with this, Marine Protected Areas and Sanctuaries
to protect the manta rays and their habitats. Other than this is
focus on reducing other human threats (marine debris, boat traffic,
nets etc). If suitable actions are taken it will still take decades for
ray populations to return to their natural state.