Manta Ray: The devilfish

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Introduction

  • Genus: Manta spp.
  • Docile nature and huge size makes them popular ecotourist attractions
  • Hunted for its gill parts and its meat for use in traditional Chinese medicine
  • Considered to be vulnerable by the International Union for Conservation of Nature (IUCN)

Distribution

Manta Rays are found in warm tropical and temperate waters all over the world but the size of their population isn’t exactly known.  Within the Coral Triangle, only Indonesia has up to date information on manta ray numbers which number at around 300 while other subpopulations around are estimated to only have less than 1,000 individuals. They often migrate to different areas in search of food and warm water and it has been estimated that they can easily travel hundreds of kilometers each day. They prefer to stay close to the surface of the water because it is where their favorite food, plankton, is located.

They are found in all CT3 countries (Indonesia, Malaysia, and the Philippines)

Why they are important

They feed on plankton and help keep the water clean which helps marine plants that depend on sunlight through photosynthesis. Plankton blooms occur when there are too many nutrients in the water or when there are no predators to eat the plankton.

They provide a sustainable source of income for coastal communities that use them as an ecotourism attraction.  It is estimated that the economic value that a single manta ray provides is $1 million USD in income over its life compared to $40 to $500 when killed for its meat. Indonesia has recognized the benefits of manta tourism to the local economy and has completely banned the hunting of manta rays within its exclusive economic zone (EEZ). This has created the world’s largest sanctuary for manta rays that is nearly 6 million square kilometers big and aims to protect its $15 million tourism industry.

Manta Ray
“Manta ray diving” by Henrik Winther Andersen (CC BY-ND 2.0)

Biology

Manta rays belong to the family Mobulidae and they are often confused with mobula rays which are smaller. One of the distinct differences that distinguishes the mobula ray and the manta ray from one another are the cephalopods that are located in front of their mouths. The manta ray has big cephalopods that curl inwards while the mobula ray’s cephalopods are smaller and are straight. The Manta Trust has a field guide that helps people identify if it’s a manta ray or a mobula ray.

Not much research has been done on Manta rays. Initial research has estimated that Manta rays have a life span of 50 to 100 years and can weigh over 2,000 kilograms. Their reproductive cycle is slow and they can take up to a year to produce one or two pups after mating.

Manta rays are filter feeders which means they feed on small organisms by filtering the water through their gills, similar to dragging a net through the water to catch all your food. Their two cephalic lobes or “horns” on the sides of their mouth help direct plankton-rich water into their mouths.  These horn-shaped lobes are the reason why mantas are also called “devilfish.” A single manta can consume about 60 pounds of plankton and small fish each day.

Manta rays are known to leap completely from the water but they are not the only species of rays to do this, mobula and eagle rays have also been observed to leap from the water. There are numerous guesses as to why they do this – to impress females, to help control parasites, to escape predators, or as a means of communication with other mantas. But up until now, it is not known why manta rays do it.

Threats

Demand for their gill and meat for use in traditional Chinese medicine is one of the primary reasons for their overfishing. There is also a demand for their skin which is marketed as exotic leather in products such as wallets or belts. However, some studies and even some practitioners themselves admit that gill plates are not effective medicine.

Manta rays are often caught accidentally as by-catch or are tangled in fishing lines. They can get tangled in nets and by the time they can be rescued they are dead or significantly weakened, sometimes manta rays are able to break free but still have the net attached to them. This can cause injury because they manta ray can continue to grow but the net can cut into the manta ray’s skin.  When these lines get caught around the cephalic fins and head, they trap the manta ray and cause it to drown. Many manta rays die from loose fishing nets and pollution.

Mantas are also affected by climate change. Rising sea temperatures disrupt the plankton’s natural ecological cycles and plankton feeders like the manta rays will find it more and more difficult to find adequate food supplies. Loss of coral reefs through climate change or pollution can hurt the mantas because it is one of their favored habitats; there is abundant food and there is the presence of cleaning-fish species such as wrasses, damselfish, and angelfish which help keep their skin clean and healthy.

What you can do

Do not buy manta ray products which can include leather made from manta ray skin, food products from their meat, and traditional medicine using their gills.

Report and share illegal sale or capture of manta rays to the authorities and social media. Malaysia does not have any legal protection for manta rays, but environmental groups are pushing for their legal protection.

Laws that protect manta rays in the CT3

Quiz

What can happen to the marine ecosystem when all the manta rays disappear?

Answer by commenting on the Facebook post by CTI-Southeast Asia!

Download the Protected Philippine Aquatic Wildlife posters

Article by Panji Brotoisworo. Art by Dana Rose Salonoy.

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