Manta Ray

The manta ray is the largest ray in the ocean and one of its most charismatic animals — a flat, diamond-shaped fish the width of a small aircraft that soars through the water on wing-like fins, filters plankton through its face, and appears to be genuinely curious about the divers it meets.

Overview

There are two main species: the smaller reef manta, which stays close to coral reefs and coastlines, and the giant (oceanic) manta, which wanders the open ocean and can span seven metres. Both are found throughout the world’s warm seas, gathering seasonally at feeding grounds, cleaning stations, and mating aggregations, and travelling long distances between them.

Physical characteristics

A manta is built as a horizontal wing. The pectoral fins are hugely expanded into triangular “wings” that flap rather than undulate, giving the manta an unmistakable flying motion. On either side of the wide, forward-facing mouth are the two cephalic fins — mobile flaps that roll up into points (hence “devil ray”) when the manta is cruising and unfurl into a feeding funnel when it eats.

Mantas are cartilaginous fish, closely related to sharks. The back is usually black with pale shoulder patches; the belly is white with a scatter of dark spots and blotches that form a pattern unique to every individual, which researchers photograph to track mantas over decades.

Feeding

Manta rays live on zooplankton — copepods, krill, fish eggs and larvae, and tiny fish. Feeding is a slow, deliberate performance: a manta swims into a dense patch of plankton with its mouth open and cephalic fins funnelling water in, then loops back through the patch again and again, often barrel-rolling to stay inside the richest layer. Where plankton is thick, dozens of mantas may form a spiralling “cyclone” or a nose-to-tail chain, each riding the wake of the one ahead.

Behaviour and intelligence

Mantas have the biggest brain of any fish for their body size, and their behaviour reflects it. They visit specific cleaning stations on reefs where small fish remove parasites and dead skin, hovering patiently and returning to the same station for years. They appear to remember individuals, both other mantas and divers, and they engage in play-like behaviour such as repeatedly riding a stream of exhaled bubbles.

Reproduction and life cycle

Manta courtship involves “trains” of males following a single female in acrobatic pursuit. After a roughly year-long pregnancy the female gives birth to a single pup — occasionally two — which unfolds from a tight roll and swims away fully independent. Because a female may produce only one pup every two or three years, and does not mature until she is 8–15 years old, manta populations grow with extraordinary slowness.

Threats and conservation

The giant manta is listed as Endangered. Its slow reproduction leaves it unable to withstand much added mortality, and it faces plenty:

• The gill-plate trade. Manta gill rakers are dried and sold as an ingredient in a Chinese health tonic, and demand for them has driven targeted fisheries across the Indo-Pacific — the single biggest cause of the decline.
• Bycatch in nets and longlines set for other species.
• Boat strikes and entanglement in fishing gear and mooring lines.
• Tourism pressure at popular sites, where crowding and contact disturb feeding and cleaning.

Manta tourism, managed well, is a powerful counterweight — a single reef manta seen by divers over its lifetime is worth an estimated million dollars or more, far exceeding its value as catch.