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An Echelon Media Company
Tuesday September 28th, 2021
Environment

First Degree Mantaslaughter

Befriending a Maldives manta. Is Sri Lanka culpable in diminished ray populations?

I met a manta in Maldives. We found ourselves in a small boat, looking for mantas with aid of a drone, snorkels at the ready. An hour earlier, we had encountered a small cluster but, having trouble with my mask, I missed most of the action. These were ‘reef mantas,’ not gargantuan ‘ocean mantas.’ Now the drone picked up a lone ray and began hovering over it, maybe 150 meters off the boat.

My eight year old Nate and I, along with his school chum and his chum’s daddy, launched into the waves, kicking furiously. A newly-wed couple jumped in behind. With the other daddy babysitting the strong-swimming schoolboys, I got slightly ahead.

Maddeningly at first, as I looked up for the drone every few seconds, I kept noting that we were not getting any closer. The drone and presumably the manta were moving slowly away. Back on the boat, they were watching and filming all this through the bird’s-eye drone camera. I heard someone yell my name. Looking up, I spied the drone straight overhead. Putting my face back in the water, I immediately saw the ray on my right-hand side, close enough to touch, swimming alongside. I got an eerie feeling that ‘she’ (as I like to think) was curious about me. Those who scuba dive amongst mantas often report an aura of fellow-feeling emanating from the rays.

Soon the others caught up. After a short while, the manta descended slowly and gracefully. Maybe the sudden celebrity made her a bit bashful. But she remained clearly in view for long minutes. We swam down for closer looks but could not reach her depth. Manifesting no alarm, she nevertheless grew bored with our company, dropped deeper, picked up speed and disappeared. Despite the earlier thrill, I felt sad.

Mantas swim around with perhaps the most remarkable fish brains in the sea, manifesting extraordinary talents. They are first of all the largest fish brains to be found. Brain volume often corresponds with high intelligence and this certainly seems confirmed with mantas, though large animals need large brains also for non-mental bodily functions. Equally significant, mantas boast exceptionally high ‘brain to body ratio’ (BBR), the proportion of brain weight to overall body weight, higher than any other fish except some exceedingly unusual warm-blooded species recently discovered. Though ocean mantas are roughly half the size of whale sharks, their brains are ten times larger. This puts mantas in a smart-learner class alongside bottlenose dolphins, chimpanzees and parrots, not to mention humans.

To be sure, the relationship of BBR to intelligence is complex, contested and controversial. Nevertheless, high manta BBR gives us an important clue. Another possible clue is that some manta brain cells resemble those of birds and mammals more than they resemble those of other fish. Mantas are unusual fish in another fascinating respect: they copulate for reproduction and give birth to live babies, without aid of placentas and umbilical cords.

Mantas seem to score especially high in inquisitiveness, learning, memory, problem solving, playfulness, coordination and communication. They have superb eyesight. They copy one another’s movements. They like to congregate and show repeat patterns of fraternization, indicating choosiness as to their ‘friends.’ Much of what they need to know, like when and where to find rich troves of food, must be learned from other mantas.

Though their behavior suggests rich mutual communication, the pathways of signaling and understanding remain a substantial puzzle. Two apparently promising theories drill down quite plausibly on visual signaling. One focuses on the fact that mantas change patterns of skin coloration, most intensely when congregating. A more recent theory focuses on appendages called ‘cephalic lobes’ located either side of their mouths. These ‘horns,’ which give mantas their popular name ‘devil fish,” help channel food inward. But a curious intricate waggling of these lobes emerges when mantas are in close company. Still a third possible communication channel may lie with electrical pulses through water at a distance.

Mantas graze-and filter feed, swimming open mouthed so as to pass plankton, krill (tiny shrimp-like crustaceans) and small fish through plates in their gills that trap their catch. They often hunt and feed cooperatively. In one typical tactic, they move forward in a kind of staggered diagonal where a ray behind and to the side of another catches prey in the bow wave of the one in front. They take turns in positions. In another tactic, they swim behind one another in a circle, sometimes in clusters of fifty or more. They draw the circle tighter and tighter, trapping prey in a densening noose.

Equally impressive, mantas seem to recognize themselves in mirrors. If so, cognizant that they exist as things in the perceived world, they may be called ‘self-aware.’ In what’s called the ‘mirror self-recognition’ (MSR) test, scientists place animals in front of a mirror. In a typical first reaction, the animal thinks it is encountering another animal of its species. It may squawk with aggression or manifest other social behaviors. Most species never move beyond this.

Across the world’s oceans, manta populations have been plummeting, with an estimated 80 percent drop-off in some regions over recent decades

In some species, however, animals launch a sequence of choreographed repetitive motions, intently observed. Scientists call this behavior ‘contingency checking’ or ‘preening.’ (This apparition does whatever I do at exactly the same time.) The animal seems to grasp that it is watching itself and may be aware of itself as a self in understanding this. Mantas placed before mirrors soon embark upon this preening behavior. They swim back and forth for long periods and position themselves to look at body parts they cannot normally see. They roll and unroll their cephalic lobes rapidly. They blow bubbles at the mirror and watch. They abstain from the coloration changes that normally go with encountering another real-life manta.

Self-awareness may go with recognition that other animals are also selves with minds of their own. In a celebrated Australian incident, an imperiled manta requested help from a diver it knew quite well. It sought attention to its problem, then lay quite still while he painstakingly removed fishing hooks lodged dangerously close to its eye.

Across the world’s oceans, manta populations have been plummeting, with an estimated 80 percent drop-off in some regions over recent decades. The most plausible explanation is that they are being heavily massacred in both purposeful hunting and in by-catch from fishing. Their extracted gill plates command high over-the-counter prices in Chinese markets for their purported medicinal and health promoting properties. There is no scientific support for the idea that gill plate consumption confers health benefits. They may in fact concentrate toxins filtered from seawater.

Manta gill plates do not even appear in the lexicon of ‘traditional Chinese medicine’ (TCM). TCM practitioners do not recommend their consumption. Consumption has proliferated only in the past few decades, promoted commercially like a patent medicine.

In addition to showing up as by-catch on fishing long lines and in nets, mantas are hunted deliberately, sometimes harpooned and sliced into pieces while still alive in order to haul them onto small boats.

Sri Lanka holds the dubious distinction of being a world leader—perhaps THE world leader—in exporting harvested manta gills. In doing so it intersects with a contraband underworld of illicit activity. Blame should not fall unduly on marginal fishermen trying to feed families. The big money lies elsewhere. As recently as this past October, Hong Kong authorities seized some 330 kilos of gill plates sourced from Sri Lanka. At, say, three kilos per animal, this comes to over 100 slain mantas. Estimates have it that Sri Lanka’s annual export averages upward of 1000 rays.

Since Sri Lanka does not boast massive manta habitat, it seems probable that much of its harvest comes from international waters and from Maldives, where ray poaching is prohibited by law. In 2012, Sri Lanka was estimated second in the world for manta gill provision, with only Indonesia ranked slightly ahead. In 2014, Indonesia banned ray hunting and gill export within its entire 2.3 million square mile exclusive economic zone. This means that Sri Lanka may now occupy the top harvest and export rung.

Depleted manta populations confront difficulty replenishing themselves. Females reach reproductive maturity slowly and gestation takes roughly a year. Pregnancy generally produces but a single offspring. Hence the average female produces one pup every three to six years in a reproductive career of perhaps twenty-five years.

In 2014, the Convention on International Trade in Endangered Species (CITES) strengthened protections, requiring special permits to trade in mantas or their body parts. This protection binds Sri Lanka as a CITES member. Permits require certification that a species offered for trade is not threatened. Sri Lanka apparently issues such permits. Any certification that mantas are not threatened provokes only puzzlement, since the entire premise of the CITES rule is precisely that rays are indeed under threat. A Sri Lankan permit for the seized Hong Kong gills was reportedly lost in transit. If it gets submitted properly, the shipment can proceed out to market.

Though some manta export may be smuggled, the bulk may well be officially licensed. Aside from CITES, Sri Lanka’s Fauna and Flora Protection Ordinance forbids non-licensed export of all indigenous ‘fish.’ Legitimate licensing applies only for exports promoting ‘scientific knowledge.’ Mantas should perhaps get listed specifically for protection under the Ordinance. Sri Lanka lists mantas as protected under the Convention on Migratory Species but has enacted no legislation prohibiting harvest. Peru, Mexico, the Philippines and Ecuador are among countries already offering rays proactive protection.

Sri Lanka should do more to curb this sinister and cynical trade.

Below is a short list of pertinent organizational resources:

  • Manta Trust
  • Manta Ray of Hope
  • Blue Resources Trust: Sri Lanka Manta and Mobula Ray Project

A graduate of Harvard Law School, Mark Hager lives with his family in Pelawatte.

Comment (1)

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  1. Benny Loebner says:

    Another fascinating article! Thanks Mark! I hope mantas are given the protection they deserve.

Comments

Comment (1)

Your email address will not be published. Required fields are marked *

Your email address will not be published. Required fields are marked *

  1. Benny Loebner says:

    Another fascinating article! Thanks Mark! I hope mantas are given the protection they deserve.