Mobula Alfredi

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Scientific Classification

  • Kingdom: Animalia
  • Phylum: Chordata
  • SubPhylum: Vertebrata
  • Class: Chondrichthyes
  • Subclass: Elasmobranchii
  • Superorder: Batoidea
  • Order: Myliobatiformes
  • Family: Myliobatidae
  • Subfamily: Mobulinae
  • Genus: Manta
  • Type Species: Mobula birostris and Mobula alfredi

Habitat, Lifespan, Weight

In 2009 the genus manta ray was re-classified into Mobula birostris and Mobula alfredi.

M. birostris is the larger of the two, is migratory, and roams the oceans. M. alfredi is smaller and lives in shallower, more coastal habitats. Both species live in temperate, subtropical, and tropical waters.

Manta rays are a cartilaginous fish in the sub-class elasmobranches and as such, they are ‘relatives’ of the shark. They are the largest and least known of all the rays. Manta rays seem to be solitary creatures, coming together only to feed and mate. According to scientific studies, manta rays from different oceans have the same mitochondrial DNA. They also have the largest brain-to-body ratio in the family of sharks, rays, and skates.

Manta rays are open ocean creatures and not considered reef inhabitants. They do frequent the reef for the purpose of being “cleaned” by small fish that live on the coral reef. These areas are called cleaning stations and serve the manta ray as a “day spa”.

With regard to weight, we estimate 50-100 lbs. per foot of manta ray.

Their life span is believed to be 50 to 100 years of age. Check out Lefty’s story, a manta we have seen in Hawaii since 1979.

Description

Manta rays have a flattened, diamond-shaped, disk-like body. They are often confused with stingrays, eagle rays, bat rays, cow rays, etc. In the family of rays, manta rays are the largest ones. Another common name for the manta ray is “devil ray” because their cephalic horns (non-feeding position) give them something of a devilish appearance.

In Hawaiian waters, we encounter manta ray “pups” with a wingspan of 2-3 feet and adults up to 12-14 feet. Mature males are up to 10 feet; the females tend to be the larger ones. It is recorded that pelagic manta rays can be up to 22 feet wide.

Manta ray coloration is primarily gray and black on the top (dorsal side) and mostly white on their bottom (ventral side) with patches of black pigmentation. The patches or black spot patterns, as well as unique physical characteristics, are used to identify individual manta rays.

Anatomy

Close-up of manta’s mouth

Range

The family of manta rays that roam the waters of the coast of the Big Island, Hawaii are considered M. alfredi or reef manta. M. birostris, also called “pelagic” manta rays are rarely seen.

Based on current scientific observation, we know that coastal manta rays can go deeper than 700 feet (214 m) for short periods of time, but they spend most of their time in shallower waters.

Scuba divers and snorkelers usually encounter the manta rays from the surface to 80 feet of depth. During our passive interaction with them, we stage the activity in approximately 30-35 feet; sometimes deeper or shallower, depending on ocean conditions and where the plankton forms.

The “Kona family” is most frequently observed at 3 different manta ray viewing sites:  “Manta Village” in Keauhou Bay, “Manta Heaven”  (Kona Airport), and near the Mauna Kea Beach Hotel (Kohala Coast).

Their home range is approximately 90 square miles, which is roughly 30 miles up and down the coast and 3 miles offshore.

Are you planning a Hawaii vacation to experience manta rays in their natural environment?

Then grab the ‘Guide to Swimming with Manta Rays in Hawaii. It includes all the things you need to know before you embark on this adventure of a lifetime!

Senses

Sight

Manta rays can see, although scientists are not sure how well. Their eyes are located on each side of their head which gives them an optimal field of vision, however, they do have two “blind spots”; one in front of them and the other one directly behind them.
It is apparent that they can see divers during the daylight hours as they often swim away from them when approached. At night, they will allow divers and snorkelers to be within a few feet of them while they are preoccupied with feeding. Manta rays also have the ability to physically pull back their eyes into their sockets to protect them.

Electro Reception

Like their relative, the shark, the manta rays have specialized nerve cells in their skin (Ampullae of Lorenzini) which give them the ability to sense the electrical fields produced by living organisms (plankton, predators, humans etc.)

Sound

Manta rays have an inner ear, which is encased in its skull. The sound waves penetrate the body by entering through two small pores located towards the front and on top of the creature. When the sound reaches the sacculus, which contains the hair-like nerve cells, their vibrations indicate the direction the sound is coming from.

Smell (Olfaction)

Manta rays have two small, nearly invisible nostrils, which are aligned with the water flow so water goes in one side and out the other. This creates a pressure difference that forces chemicals over the sensory folds and past mucus and cilla which allow them to detect concentrations as small as one part per million.

Touch

Similar to human skin, manta rays seem to have a sensitivity to touch over their entire body. Further, their skin is covered with a slime coating, which serves as a barrier to bacteria, aids in healing in the event of injury, and reduces friction as they swim through the water.

Taste

Towards the back of their oral cavity, manta rays have very small protrusions, which can detect minute chemical concentrations. This gives them the ability to sense and consume their natural food source as well as to detect species-emitting chemicals from potential mates.

Are you planning a Hawaii vacation to experience manta rays in their natural environment?

Then grab the ‘Guide to Swimming with Manta Rays in Hawaii’. It includes all the things you need to know before you embark on this adventure of a lifetime!

Behavior

Feeding

Manta rays are filter-feeders. They filter the plankton out of the water using a complex system of traps, filters, and gill combs. They also have fins in the front, called cephalic fins. These fins can be rolled and unrolled during feeding.

When cephalic fins are unrolled, they help channel the plankton- filled water into the mouth. When manta rays are not feeding, they roll up their cephalic fins and close their mouth to become more hydrodynamic. During the feeding process, the rays will often do back rolls in the water. It is believed they do this so as not to swim away from plankton-rich areas in the water column.

Due to conditioning by humans over a period of decades, the manta rays found in nearshore waters of the coast of West Hawaii have learned to associate light with the presence of their natural, planktonic food source. When divers gather on the bottom during the dive and the snorkelers are on the surface, the lights cause the planktonic marine life, if present, to concentrate. If the manta rays are in the area, they will be attracted to those lights and will feed on this plankton by swimming various patterns.

It is apparent that they can see divers during the daylight hours as they often swim away from them when approached. At night, they will allow divers and snorkelers to be within a few feet of them while they are preoccupied with feeding. Manta rays also have the ability to physically pull back their eyes into their sockets to protect them.

Diet

Their diet is zooplankton which consists of copepods, mysid shrimp, crab larva, mollusk larva, and fish eggs. Manta rays must eat approximately 12% of their body weight in plankton per week. The manta rays swim slowly and gracefully while they are feeding. Their large mouths open and their cephalic horns will unroll to funnel the plankton into their oral cavity.
There is also a study underway to determine if the manta rays have a preference for a specific type of plankton and whether or not this affects the migration and congregation of the animals along the coastline. Thus far, the results have been inconclusive. It has been determined that approximately 10,000 specimens of plankton equal 1 dry ounce of weight. A manta ray is constantly searching for and consuming planktonic marine life.

Breaching

Occasionally we will observe a manta ray swimming out of the water and then falling down on the surface making a loud noise. No one knows for sure why they do this or what purpose it serves. Some common thoughts are to elude predators, remove remoras or other parasites, and communication.

Defense

Manta rays are generally thought of as harmless creatures. They do not have barbs, a venomous stinger, or teeth. Because of the large surface area of their pectoral fins, they are capable of bursts of high speed, which they use to escape predators. Their defense mechanism is simply “flight”. Their maneuverability and speed make them hard to prey on. Their natural predators are most likely large sharks.
This is why it is important not to startle them. The manta ray could swim rapidly into a diver, snorkelers, or a coral head, which might result in an injury.

Mating – Courtship

The ventral pelvic fin area distinguishes female and male manta rays. Females have flat pelvic fins. Males have claspers that begin at the base of the pelvic fin and extend out past the fin as the manta ray matures. Males also have glands at the base of each clasper that appear as small lumps. When a female manta ray is ready to mate, she emits a species-specific concentration of chemicals called pheromones, which trail along behind her as she swims. The males can detect these chemicals in very small concentrations. This alerts them that she is ready to mate and gives them a way to find her by following the “scent”.

Several males have been observed in courtship behavior following a lone female in caravan fashion or “manta train”. While attempting to mate, the male swims above the female and inserts one of his claspers into her cloaca to achieve egg fertilization. The claspers are extensions of the pelvic fins and are the means by which the male manta ray delivers sperm to the female. The male has two claspers, but only one is used when fertilization is attempted. Prior to transmission of sperm, a gland is activated at the base of the claspers, which secretes a thick fluid, which contains proteins and lipids. Not much is known about this fluid or its purpose, but scientists theorize that it may have something to do with lubrication of the clasper groove; perhaps to prevent loss of sperm during copulation.

Reproduction

Manta rays are “ovoviviparous”, meaning the young hatch from an egg inside the mother and the mother gives birth to a live well-developed pup. The young are almost exact replicas of the adult form; just smaller. Females produce only one “pup” at a time.

At birth, the pups are expelled from the female’s oviduct and appear cigar-shaped with the two pectoral fins rolled around the pup like a “burrito”. They appear to be about 2 to 3 feet across shortly after birth. The adult female provides no post- parturition care as they are not paternal animals. This means that after birth, the pups are on their own.

The gestation period is 13 months. It is believed that sexual maturity in males and females is reached at 10 to 15 years.

Manta rays in captivity

There are manta rays in captivity at the Atlantis Resort in the Bahamas. The aquarium is quite large (several million gallons) and the manta rays feed on small shrimp, which are introduced into their mouth from an attendant on the surface (while it is swimming) using a small net. It is unknown if the manta rays are in good health or suffers any ill effects due to its confinement. Manta rays are also held in captivity in the Okinawa Churaumi Aquarium in Okinawa, Japan, the S.E.A Aquarium in Singapore and three manta rays are in the Georgia Aquarium in Atlanta, Georgia, USA. Here is more information about where to see mantas in aquariums.

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