Biology & Behaviors
Mantas belong to the Elasmobranchii which include sharks, skates and rays, and are part of the Mobulidae family of Devil rays. Their subfamily of Myliobatidae includes two species of Manta and 9 species of Mobula devil rays. Palau’s mantas are Manta alfredi , or reef mantas. The other, larger oceanic Manta birostris species has not yet been recorded from Palau. At least three devil ray species have been photographed in Palau.
The name manta comes from the Spanish word “Mantilla” or cloak. First described in 1798, it was believed there was one single species of manta until 2009, when Dr. Andrea Marshall identified the difference between the two current species. She believes there may even be a third manta species. It is now believed there may even be more than two different manta species or subspecies.
The manta is one of the largest, but least known fish species. They do not possess a hard bony skeleton, and unlike most other ray species, they do not have a stinger. Although they swallow their food whole, they still have around 4,000 tiny teeth on their lower jaw, that seem to be only used during mating, when the male grabs on to the female’s wing
Each manta is born with a belly spot pattern and back pattern that is unique, like a finger print. Therefore they are easy to identify with photographs, especially of the belly spots. The unusual black or melanistic morph manta variation is almost completely black above and below, with a white and black spot belly pattern and is sometimes lighter around the mouth. The even rarer white manta morph has not yet been recorded from Palau, although some regular mantas are very light colored and one small individual has been observed “losing color” over the years. The black mantas are seen feeding around regular mantas, but rarely join the trains or interact with them, and in general seem to be loners. Out of the over 200 manta rays identified in Palau, some have been filmed and photographed showing unusual feeding behavior, where they feed sideways, and with their lobes sticking straight out instead of funneled. No black mantas have shown this behavior.
The manta ray’s pectoral fins have evolved into wings and their skin is covered with a mucus to defend against infection. They have a small dorsal fin located at the base of their long and narrow tail, which does not have a spine or stinger. Mantas have the largest brain relative to body size compared to other Elasmobranchii and fish species, and sophisticated senses for hearing, touch, vision and electrosensory systems. From years of interacting with the same Mantas at German Channel, it is obvious that they are highly social creatures, who recognize individual divers, and clearly show individual behavior and character. Mantas are sometimes seen leaping completely out of the water for unknown reason, this could be to remove remoras, part of mating behavior, assist in giving birth, or as a signal to other mantas in the area.
Although there are few local threats to mantas aside from boat strikes, fishing lines and hooks, and tourism pressure in Palau, the new increased Asian demand for dried manta gill rakers could cause long line vessels operated in Palau and commercial fishing in nearby Indonesian and Philippine waters to target Palauan mantas, depending on their range and movements across borders, which we still know little about.
Cleaning
Cleaning stations on the reef are certain locations where fish come to get their skin, gills and teeth cleaned from parasitic copepods by a variety of small cleaner wrasse species. Mantas spend hours each day getting cleaned, and often even wait in line for their turn to get cleaned. Shown here is the most well-known cleaning station at German Channel, where mantas come up a deep sandy slope regularly to get cleaned at an isolated coral head about 50 feet deep. There are several other cleaning stations along this same stretch of reef, and dive guides have noticed lately that the mantas are moving more to the other, deeper cleaning stations, perhaps to get away from the large number of divers crowding around and flashing strobes at this popular cleaning station.
Feeding
Mantas can be seen feeding alone or in aggregations, on small planktonic organisms and occasionally small fish that are filtered from the water as they swim with their mouths open. When the incoming current is strong, they come close to the surface and unfold their cephalic fins to funnel the plankton into their wide-open mouths. They sometimes feed in “trains”, one manta closely following another. When the current is less, they start “barrel rolling”, doing back-flips to push the plankton into their mouths, on the surface or sometimes below 100 feet deep. When strong winds and currents drive the plankton inside the reef, mantas can be seen rolling around and feeding like a vacuum on shallow sandy bottoms far inside the lagoon, depending on where the plankton settles. Mantas have also been seen feeding on the surface with most of their back sticking out of the water, sometimes making funny up-and-down movements with their back, perhaps to stimulate the plankton movement, or maybe the waves just feel good on their skin.
In Palau, gatherings of other plankton-eating fish species such as fuseliers, mouth mackerels and black snappers are often good indicators for where mantas will show up to feed around channels. When the currents are right, these fish will form large feeding “balls” near the surface where the plankton is thickest, and often mantas will join them and keep circling the same area while feeding. Once feeding starts they may stay around for an hour or more depending on the current.
Courtship & Reproduction
The sex of a manta can be determined by the two claspers only visible on the inside of male pelvic fins. Sexual maturity can be confirmed in females if they have mating scars on their wingtips, and in males is believed to be when their claspers extend well beyond the pelvic fins. Between October and May we see courtship trains in Palau, with several males competing for and following one female. Actual mating has only been filmed on rare occasions, while the live birth has not been filmed or photographed yet in the wild. We know from other countries that when mating trains form, a male follows a female from behind, grabs a female by her wingtip with his Velcro-like teeth, usually the left wing, and flips her to position her belly to belly with him, and inserts his claspers for 1-2 minutes. This is similar to most shark and ray species mating behavior, but it takes place near the surface in the water column, not on the bottom.
Mantas are oviparous, which means they give birth to a live pup that hatches from an egg inside the mother. Gestation is about a year. A pregnant female close to giving birth has a clearly round belly and visible “hump” on her back. The only reported births in captivity have been in the Okinawa Expo Aquarium in Japan.
Newborn pups are about a meter across when born, much larger than you would expect, and grow very rapid the first year. They are abandoned by their mom immediately to fend on their own. They are seen around the cleaning and feeding areas near the adult mantas in Palau, and seem eager to copy their every movement, but are ignored by the adults and not allowed in the feeding trains. The females usually mate again almost immediately after giving birth, and are believed to be able to get pregnant every 1-3 years.
Observations from the last years have shown that during the months of October to April each year, pregnant mantas come to the channels around Palau to give birth and mate, and on average we see 2-4 newborn manta babies around the cleaning stations.