American Oceans
giant manta ray

Giant Manta Ray

The giant manta ray, also known as Mobula birostris or Mantra birostris among scientists, is one of the 630 different species of ray known to humankind. Due to overhunting and other human industrial activities, the IUCN (International Union for Conservation of Nature) lists the giant manta ray as “Endangered.”

Characteristics and Appearance

Even before birth, giant manta rays are just that—giant. Embryonic manta rays can measure up to 50 inches wide from wing to wing, and they can weigh over 20 pounds. At birth, giant manta ray pups typically measure 3.7 to 4.7 feet wide.

Giant manta rays are also sexually dimorphic. That means you can tell whether an individual giant manta ray is male or female based solely on looking at them. While giant manta rays’ visual differences come down to a lot more than biological sex, sex is one aspect that influences each ray’s appearance.  

Weight and Length

Female giant manta rays are larger than males, having a wingspan of 18.3 to 22.7 feet. Males, meanwhile, measure 17.3 to 20.3 feet from wing to wing. Giant manta rays can grow past those averages, though, with the widest one known to researchers measuring 30.3 feet. They can weigh anywhere from 2643 to 3084 pounds.

Physical Characteristics and Color

Giant manta rays’ backs run a gamut of colors, from brown to blue to black. They have white underbellies with unique, dark splotching patterns. Sometimes, giant manta rays will have light-colored splotches on their backs, too. Researchers have used both of these patterns (or lack thereof) to identify individual manta rays.

Their skeletons are made of cartilage (the same substance that makes up human ears and noses) to help giant manta rays manœuvre effectively through the waters. They also have lobes that point from their heads, which they roll up while swimming and lay flat while eating. Meanwhile, you find their gills on their underbellies.

Of course, the most distinctive physical trait of the giant manta ray is its wing-like fins. Giant manta rays are born with their fins wrapped around them, but they unwrap themselves relatively quickly. Giant manta rays’ wingspan is longer than their head-to-tail size.

Lifespan and Reproduction

Giant manta rays are polyandrous, which means that one female will take on multiple male partners in her lifetime. The courtship rituals consist of a female giant manta ray swimming faster than usual—5.6 to 7.5mph—as a group of males pursues her. 

After no more than half an hour of the chase, the female will slow down and allow a male to bite onto one of her wings. The male will then slide under her, place his clasper into her cloaca, and deposit sperm. This transaction lasts about one-and-a-half to two minutes. Afterward, the chase will resume, and a second male will be allowed to mate with the female.

When male manta rays reach 13 feet in width, and when females reach 16.5 feet, they are considered sexually mature. Typically, this development takes five years.

Giant manta rays mate from December through to April. Courtship and mating take place in waters with temperatures of 79ºF to 84ºF and reefs 33 to 67 feet deep. Gestation takes 13 months. Following this period, pregnant females will give live birth to 1 to 2 pups. As soon as the infants’ wings unwrap, they can protect themselves.

On average, giant manta rays live for 18 to 20 years.

Habitat

Giant manta rays live in warm, tropical ocean waters and inhabit reef and coastal biomes. They do not dive very deep, usually only going down 40 feet. While they will venture out away from shorelines, they tend to stay closer to them. There is more food available to giant manta rays along shores.

Where Does the Giant Manta Ray live?

These creatures have been found as far north as Massachusetts and as far south as Tasmania. Scientists believe giant manta rays could also live as far north as Russia and as far south as New Zealand.

Giant manta rays congregate the most along:

  • the west coasts of the United States and Mexico; 
  • the Caribbean; 
  • the east coast of South America;
  • the Horn of Africa, and 
  • the islands of Southeast Asia.

Food and Diet

Giant manta rays eat by filter feeding. They use their mouths and their frontal lobes to gather up prey. They then suck up the water. Prey will get caught in filtering tissues at the back of the rays’ mouths. At no point do giant manta rays use their teeth to eat.

Researchers have noted that giant manta rays will swim in long ovals as they hunt and feed. Experts don’t know the exact reason for this behavior, but they think it might be to keep prey animals as close to the feeding rays as possible.

What Does the Giant Manta Ray Eat?

Giant manta rays are carnivores. More specifically, they are mostly planktivorous—that is, they eat plankton most of all. Also, giant manta rays will eat small fish and shellfish.

Threats and Predators

As with most, if not all, endangered animal species, the giant manta ray’s biggest threat is human activity. 

Human Threats

One of the most pressing threats humans pose to giant manta rays is the fishing industry. People will hunt manta rays for their gill plates first and foremost, with food and other uses being contributing factors, too. Moreover, when industrial and non-industrial fishers aren’t necessarily looking to catch giant manta rays, these creatures can still get caught in nets and other equipment.

Ocean pollution is another possible issue for giant manta rays. Researchers are concerned that waters polluted by oil, acid, and other contaminants contribute to population depletion among giant manta rays.

Climate Change and Global Warming

Climate change impacts giant manta rays due to how it affects their prey. When ocean waters get warmer, it can disrupt plankton life cycles, causing their numbers to drop. As such, scientists fear the giant manta ray will see negative repercussions to its lifestyle and life cycle. These disruptions could further devastate giant manta ray population numbers. 

Predators

The only natural predators of the giant manta ray are some species of shark. Because giant manta rays are so big, most animals do not see them as potential prey.

Other Threats

Parasites will occasionally attach themselves to manta rays’ bodies, though they are not a significant threat to giant manta rays overall.

Conservation Status

The IUCN lists the giant manta ray as “Endangered.” This classification means giant manta rays are at “a very high risk” of going extinct.

The CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) has placed restrictions on trading giant manta rays. Certain countries, such as Maldives and Indonesia, have also restricted or banned giant manta ray hunting.

Fun Facts About the Giant Manta Ray

  • Giant manta rays have a symbiotic (mutually beneficial) relationship with remoras. These fish get to feed off parasites and feeding-remnants on rays’ skin. The rays, in turn, get a nice grooming job.
  • Giant manta rays get along very well with humans! They’re so friendly that entire tourism industries have been built around diving down to see these friendly creatures up close. Sometimes, giant manta rays will try to get people’s attention instead of the other way around. Of course, other times, manta rays want to avoid human interaction.
  • With that in mind, giant manta rays pose absolutely no threat to us whatsoever. They are not interested in hunting us down for food—and unlike sharks and their prey, giant manta rays can’t mistake us for prey.
  • Sailors used to think giant manta rays were violent creatures who would crash their ships. Thankfully, we all know better now.
  • The word “manta” comes from the Spanish word for “blanket,” which is appropriate given their overall shape.

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