Rays: Manta Rays, Mobula Rays, Stingrays, Skates & Electric Rays
Forty-two species of rays from 9 families and 3 orders have been found in Sri Lankan waters both inshore and out at sea in depths of up to 200m. Rays generally live and feed on planktonic animals at the bottom or close to it – one notable exception is the Oceanic manta ray, which glides through the open ocean feeding on plankton near surface to depths of up to 1,000m. It is the largest ray which can grow up to 7m across and can weigh 1.5 to 2 tonnes! Female is larger than male. Reef mantas are smaller and about half the size of the Giant manta. Mobulas are also smaller with a wingspan of about 2 to 3m and are found in schools.
The sociable and graceful manta and mobulas are an in-water must-see item on the checklist of enthusiasts. While rays are not aggressive towards divers, a diver should never touch a ray or any wild animal. At best you will frighten it away especially if you approach it from behind. Seasonality for ray species is largely unknown pending further research.
Ray fisheries in Sri Lanka is notably one of the largest in the world and is primarily driven by an export industry for gill rakers where most profits are made outside Sri Lanka. Although gill rakers are used in Chinese medicine there is no scientific proof that they have any medicinal value.
Why Protect Rays in Sri Lanka
Manta rays are listed under CITES App 2 (controlled and managed sustainable international trade) and, both manta and mobula rays under CMS App 1 & 2 which technically means that Sri Lanka should give them total protection and not catch them.
Rays have the potential to attract large numbers of tourists each year amounting to several millions of dollars in foreign earnings. A significantly better income generating alternative to gill raker harvesting. In this case, a live manta is worth more than 1,000 times a dead manta.
Rays help regulate populations of species in the ecosystem and are key indicators of the health of an ocean's ecosystem.
Their slow growth to reach maturity (about 10 to 15 years) and reproduce relatively few pups within a relative short lifespan makes them susceptible to overexploitation constraining their ability to recover from a depleted state.
Rays cannot recover as rapidly as many faster growing fish can if their populations are depleted.
Sri Lanka should join and support international conservation and protection of rays because manta and mobula rays traverse geographic and international boundaries and interbreed during their lifespan.
Biology of the Manta and Mobula Rays in the Indian Ocean by Daniel Fernando.
Be AWARE! Not all and only some rays are capable of stinging including those that inhabit shallow waters near sandy beaches. You should use caution when swimming in these areas. To avoid contact with a potential stingray drag your feet in the sand as you walk. This will alert a stingray to your presence and then it will likely move away before it does any harm in self defense. If you are stung, get out of the water and seek medical attention to make sure the sting is treated properly.
Legend in table below:
* indicates species or subspecies taxonomy not fully elucidated.
# indicates presence in Sri Lankan waters unconfirmed.
^ indicates species possibly extinct.
Sharks and rays belonging to the Sub-class Elasmobranchii are organized in two infraclasses of which all sawfishes, skates and rays are all included in Batoidea. From an evolutionary standpoint, rays are relatively recent dating back some 20 million years.
Batoids are distinguished by their flattened bodies, enlarged pectoral fins that are fused to their bodies and head, and gill slits that are entirely on their ventral surfaces. The upper edges of the orbits are attached to the eyeballs so that they do not form free eyelids. Many species of batoid have developed their pectoral fins into broad flat wing-like appendages which they use in an elegant, wave-like motion. The anal fin is absent.
Consumer demand for gill rakers (Chinese medicine) and sawfish rostrum.
Unregulated / over-fishing resulting in population decline.
Non-discarded bycatch in tuna gillnet fisheries. An entire school of mobula rays can be wiped out by a single gillnet.
Illegal fishing practices (eg. dynamiting, "Leila" nets).
Polution (Arsenic, Cadmium, Lead, Mercury, etc.).
Habitat degradation due to increasing human activities.
Rays are identifiable by their unique shape and behaviour. While all rays have flattened bodies, the type of ray can frequently be distinguished by its body shape (diamond, round or triangular), its method of swimming, thickness of its tail, and the presence of stings or barbs.
Both manta rays and mobula rays have 5 gill slits on the ventral part of their bodies. A manta ray can be distinguished from a mobula ray by its great size and evenly aligned terminal jaw (middle of the head) as compared to the mobula's undercut, ventral lower jaw. They are incredibly graceful underwater, and can move quite quickly with seemingly effortless movements of their pectoral fins. They breach occasionally, leaping from the water and even backflipping in the air. Download a field guide.
Stingrays have a characteristic diamond shape and are easily identified by their elongated, thin tails with barbed stings and by the fact that they are frequently found half-buried in the sand. However some stingrays, such as spotted eagle rays, are more commonly observed free-swimming.
Skates appear quite similar to stingrays. Instead, of stings they have sharp barbs along their spines or on their tails for defense. Skates also have wider tails than stingrays, with small fins near the tip of the tail. Finally, skates are round or triangular shaped with elongated noses, as compared to the typical diamond shape of most stingrays.
Electric rays are smaller than many other types of rays, and do not have barbs or stings. Instead, they stun their prey with electric shocks. They are more rounded shape than other rays. They have rounded dorsal fins and thick tails. Unlike other rays, electric rays use their tails to swim, not their pectoral fins.