Keeping Giant Manta Rays around Tobago

The recent sighting of a Giant Manta Ray at Buccoo Bay prompts Shivonne Peters, marine scientist, to consider the simple measures needed to keep these and other creatures in Tobago waters, and to build an attractive marine-based tourism industry.

 Two weekends ago, beachgoers at Buccoo Bay were startled by the sight of a pair of black fins rising out of the water only a few meters from shore. At first, these fins were presumed to belong to some species of shark; an equally thrilling sight but also rather uncommon along Tobago’s populated beaches. Bathers scampered into ankle-deep waters but remained in awe of the creature that seemed unbothered by their presence. For over half an hour, we watched as this majestic animal, now decidedly not a shark, cruised gracefully along the beach performing the occasional somersault extending parts of its body out of the water. Every evening for the entire week, this animal exhibited the same behaviour and pattern of movement, a swim along Buccoo Bay eventually disappearing into the deeper waters at sunset.

 

The Giant Manta Ray in Buccoo Bay, Tobago

The Giant Manta Ray Manta birostris, is no stranger to Tobago’s waters. A favourite with divers and snorkelers, Manta Rays are recognizable by their flat, diamond-shaped body and long extending ‘wings’ or pectoral fins. The tips of the pectoral fins roll upwards while swimming and often breach the water’s surface. With a wing span of up to 29 feet, it is the largest species of Ray (fish that are comprised of cartilage rather than bone) found in tropical, sub-tropical and temperate waters around the world. The animal is mostly black in colour with a white belly or underside, each with distinct spotted patterns (used by scientists and divers to identify individuals). Its wide mouth, stacked with 18 rows of non-functional teeth (not used for feeding), is found on the front end of their bodies with gill openings or gill rakers on the underside of the animal.

Unlike their relatives the Stingray, Manta Rays have a shorter, spineless tail along with a host of noticeable differences in appearance, diet and behaviour. One distinguishing feature is the venomous spine or barb located at the base of the Stingray tail. This is utilized only as a defence mechanism and that animal is considered non-aggressive to humans. Stingrays feed on small crustaceans found on the ocean floor while the Manta Ray consumes plankton (microscopic organisms) and even small fish. These filter feeders can consume up to 30 kilograms of plankton a day and are known to exhibit barrel rolling (rolling backwards) when plankton is abundant.  Stingrays are frequently seen along the sandy seafloor of coral reef habitats and are even known to forage for discarded fish (and fish entrails) alongside jetties. Earlier this month, hundreds of American Cow Nose Rays gathered in Chaguaramas, a rare and spectacular sight, possibly signalling the start of their annual spring migration.

 

The Stingray, relative of the Manta Ray, in Coral Gardens, Buccoo Reef, Tobago

In other parts of the world, including Thailand and Ecuador, Manta Rays are considered  seasonal visitors to coastal sites. Occasionally, they gather at cleaning stations where they employ the help of other smaller fish (remoras and wrasses) to remove parasites. Yet, the possibility of seeing Manta Rays year-round may be one of Tobago’s most sought-after assets in the diving industry. These graceful creatures are quite approachable and quickly become accustomed to divers in their habitat. In the past, divers have been known to hitch a ride on these animals, a practice that has long been discontinued but indicative of their docile nature. Whether it’s as far north as Batteaux Bay (Speyside) or at Grange Bay along the south-west coast, Giant Manta Rays thrive in Tobago’s warm and highly productive seas.

Like countless other marine species, the Giant Manta Ray is subject to threats, many of which are because of human actions. Due to their size, they have few natural predators including sharks and killer whales, yet are considered a threatened species (at risk of extinction) under CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora). Manta Rays are caught both intentionally for their gill rakers (an important ingredient in traditional Chinese medicine) and unintentionally (as by-catch). The demand is especially high in the Philippines, Indonesia, Tanzania, India, Madagascar and Peru. The Manta’s flesh, when not discarded, is dried and used as animal feed. They are also commonly entangled in fishing nets causing them to remain motionless and restricting the flow of water over their gills. Low fecundity (eggs produced during a spawning season), slow growth rates and lengthy gestation periods (1 year) together with pressures from the fishing industry contribute to the declining populations of Giant Manta Rays worldwide.

Fortunately, Giant Manta Rays are not subject to such threats here in Tobago. In fact, these creatures, like many other marine species such as turtles, sharks and reef fish are far more valuable as living resources. Dive tourism, which is already established in Tobago on a moderate scale, is especially promising as a means of revenue generation for the country. Some opponents may argue that divers disturb wildlife; in the case of the Manta Ray, touching them removes the protective mucous layer on the skin. Dive instructors in Tobago are well aware of the risks to the animal and encourage divers not to interfere with them in any way.

To encourage further growth in this sector, as well as the wider tourism industry, we must maintain healthy ocean ecosystems. From the top predators (sharks) to the microscopic plants, each organism plays a vital role.

Mechanisms should also be implemented to reduce pollution (including land-based sources) and encourage the sustainable use and preservation of our coastal and ocean resources. Preservation efforts through marine sanctuaries have been rather successful in other countries. The Gulf of Mexico is now home to the first known Manta nursery in the world, an area of immense scientific and ecological value. Establishing other Marine Protected Areas in Tobago, particularly in known Manta Ray habitats, can also increase their populations around the island. It is not surprising then that many sightings have been documented in and around the Buccoo Reef Marine Park, the only Marine Protected Area in Trinidad and Tobago. With some of the most diverse reef habitats right in our own backyard, our actions today will allow us continued sightings of these magnificent creatures well into the future.

About the Author: Shivonne M. Peters is Managing Director of Seven Environmental- a Consultancy Company focused on the marine sector. She is currently a PhD candidate in Marine Sciences at the University of Trinidad and Tobago. For further information email sevenenvironmental@hotmail.com.