Mantas and devil rays

The term “manta” corresponds to the Portuguese or Spanish word used to refer to a blanket-like cloak similar to mobulids in size and shape.

Mobulid rays belong to the family Mobulidae, which has ten species and comprises one genus: Mobula.

Even though these are amongst the most charismatic of marine species we still know very little about their biology and ecology and they are facing serious threats. These rays are affected by numerous human activities including directed fisheries, incidental capture as by-catch, habitat destruction, marine debris, boat strikes, entanglement and unregulated tourism.

Mobulids mature late, have long life spans, and they give birth to a single pup every 2 to 5 years, which limits the capacity of populations to recover from depletion caused by human activities or other impacts. It is therefore increasingly important to raise awareness about the importance of the conservation of these animals.

Close relatives of all sharks and rays, these cartilaginous, filter-feeding fish range throughout the tropical and sub-tropical oceans of the world. These fish must keep water flowing through their gills to breathe, which means they can never stop moving. Their daily and seasonal movements are synchronised with ocean currents to allow them to chase the planktonic food on which they depend.

Several morphological differences, such as their body size and colour, set the species apart. Manta rays are the largest of all rays, reaching a maximum size of seven metres from wing tip to wing tip, and weighing up to two tonnes. Their size enables them to increase their foraging range and energy storage capacity, and the flattened body shape is perfectly suited to gliding, improving the swimming efficiency of these large fish.

Devil rays are their smaller relatives, with most species ranging between 1 and 1.8 metre disc widths. The spinetail devil ray and sicklefin devil ray are the largest species, at widths of up to 3.5 metres. Despite being known for their dark dorsal side and white ventral side, the colouration and spot patterns vary among species.

Manta and devil rays use specially modified cartilage-supported appendages, called gill plates, to filter zooplankton and small fish from the water column. While swimming, the mouth is kept open, and the cephalic lobes are used like a spoon to facilitate the intake of food. Once it is swallowed, the food is filtered by the gill plates before being processed by the digestive system. Although they are filter-feeders, most species have 300 rows of small, peg-like teeth, each about the size of a pinhead, which they are used in courtship and mating.

Mobulid rays have large brains, having the highest brain to body mass ratio of all fish and a brain physiology which is closer to that of mammals than other fish. Their large brain size could be associated with their complex behaviours and apparent “social intelligence”. Their curiosity in relation to divers makes any encounter with a manta or devil ray a truly magical experience. Besides having a large brain, mobulid rays have a huge sponge-like network of arteries around the brain called rete mirable cranica. This network forms a counter-current system that facilitates the exchange of heat between the blood vessels. It is an important adaptation that allows them to keep the brain well-heated and active while they are diving to forage for small fish and other zooplankton species that abound in deeper layers of the ocean.

Click here to know more about mobulid ray species found around the globe.