Giants quietly disappearing

We published this article in issue 6 of ThisWildEarth. Read more exciting stories on our other publications.

They are curious and incredibly graceful. Yet across the world, giant manta rays are being hauled from the ocean and cut apart for a dried product with no proven medicinal value. Much of the slaughter happens far from public view, hidden in fisheries’ data and anonymous coastal markets, as one of the marine world’s most extraordinary animals slips quietly towards crisis. By René Laing

By the numbers

·       260 000 Manta and devil rays are caught annually

·       Declines of up to 90% in some regions

·       1 pup every 2–3 years

·       It takes about 10 years to reach maturity

·       Gill plates equal roughly 1% of their body weight

A dark silhouette rises slowly from the deep, wings stretched nearly seven metres from tip to tip. With an effortless sweep, it glides forward, moving gracefully through the water, almost like a bird in flight. There is something almost unreal about the encounter, a combination of immense scale and complete gentleness that tends to stay with those who witness it.

“What stands out most is their behaviour,” says Dr Guy Stevens, co-founder and chief executive of the Manta Trust.

“Oceanic manta rays (Mobula birostris) are highly intelligent and often display a natural curiosity, sometimes approaching divers and maintaining eye contact as they glide past. “Despite their size, they are gentle and non-threatening.”

That sense of calm, however, contradicts what is unfolding across parts of the world’s oceans. One of the sea’s most graceful giants is being killed in growing numbers, not for a product of immense size or obvious value, but for a bit of dried tissue.

What makes this more profound is that the oceanic manta ray became recognised as a distinct species only in 2009, separate from the reef manta ray (Mobula alfredi). Yet just two years later, it was listed as Endangered on the International Union for Conservation of Nature Red List.

More value dead or alive?

Inside the manta ray’s mouth are rows of delicate cartilage filaments known as gill plates. These help to filter plankton from seawater. The thin, comb-like structures have become valuable in parts of Asia for traditional health tonics, even though there is no scientific evidence supporting any medicinal benefit.  

Gill plates account for a tiny percentage of a manta ray’s body weight and even less once dried. A creature spanning nearly 7m is ultimately reduced to a fine powder that weighs next to nothing. Yet this helps sustain a global wildlife trade operating with far less public attention than other forms of exploitation.

Recent global analyses by the Manta Trust estimate that more than 260 000 manta and devil rays are killed every year, with most of this from small-scale fisheries. Further, research published in Environmental Biology of Fishes found that mobulid rays, the broader umbrella term under which they classify different ray species, are caught in at least 43 countries, consumed in more than 35 nations, and exported through a specialised gill-plate trade involving at least 14 countries. Those numbers are likely conservative, as fisheries’ records frequently fail to distinguish between distinct species.

Unlike elephant ivory or rhino horn, manta ray products do not generate iconic images and international outrage. Gill plates are small and easily concealed among dried seafood products, while many of the animals are landed through coastal fisheries that receive little international scrutiny. By the time the animal enters trade, the fish itself is no longer visible, reduced to sacks of dried gill plates moving through markets.

From bycatch to target

For many years, manta rays were landed accidentally as bycatch in fisheries targeting other species. But over the past two decades, that pattern has changed as demand for gill plates has created an incentive. “In some regions, manta rays are now directly targeted, while bycatch remains a major global issue,” explains Stevens. Industrial tuna fishing frequently overlaps manta habitat, leading to entanglement in gillnets and capture on longlines, while some small-scale fisheries now land them deliberately to meet demand for gill plates and meat.

“Even when caught unintentionally, manta rays often suffer high mortality,” Stevens says, “either during capture or shortly after release.” They are extremely sensitive to stress and need to move to breathe. The result is that the species faces pressure from multiple sides across vast stretches of its range.

Gaps in enforcement and fisheries’ management add further pressure, particularly in international waters and regions with limited monitoring capacity. Recent research has also revealed another emerging threat. Studies comparing remote protected coastlines with heavily developed marine areas, show significantly higher injury rates in manta rays linked to vessel strikes and fishing gear in regions with intense human activity.

Downward trends and hope

“There is growing evidence of significant population declines across multiple regions,” Stevens says. “In some locations, we have seen declines of more than 90%.” Troubling hotspots include the Indian Ocean and parts of Southeast Asia and South America, with Indonesia, India, Sri Lanka, Peru, and Myanmar accounting for a substantial share of the global catch.

For a species with slow reproductive rates, these declines are not losses that can be quickly regained. In many areas, each removed breeding adult represents years of lost recovery potential. “Oceanic manta rays take close to ten years to reach sexual maturity and typically give birth to just one pup every two to three years.” This makes them one of the least-reproductive large marine species in the ocean.

Even under favourable conditions, population recovery can take several decades. Once breeding adults are removed from a population, replacement is measured in decades, making sustained fishing mortality particularly devastating.

There are signs that science and policy are catching up with the crisis. “The recent uplisting of all manta and devil rays species to CITES Appendix I represents a major milestone,” Stevens says. The decision effectively closes legal international commercial trade in manta and devil ray products and marks one of the strongest international acknowledgements yet that the group is in serious trouble.

Yet CITES listings alone will not reverse decades of loss. “Meaningful conservation outcomes will depend on effective implementation,” Stevens cautions, “including stronger national protections, better fisheries monitoring, reduced bycatch, and meaningful enforcement in the regions where exploitation remains highest. Without those interventions, it risks becoming little more than symbolic paperwork.”

However, not everything is unwelcome news. Researchers have identified what appears to be the world’s largest known population of oceanic manta rays off Ecuador, where more than 22 000 individuals have been recorded, over ten times larger than typical subpopulations elsewhere. Stevens explains that findings such as these highlight how highly productive ocean regions, driven by nutrient-rich upwelling, can support large aggregations of these animals.

Stevens argues, however, that public awareness remains a critical missing piece. Unlike more famous marine species, manta rays remain largely out of sight for most people, with direct encounters usually limited to divers, snorkellers, and marine enthusiasts. That lack of visibility has allowed much of their decline to unfold quietly and with relatively little global attention.

Giant manta rays may be among the most graceful animals in the sea, but grace offers no defence against hooks, nets, and illegal markets. If the current trends continue, encountering these ocean giants may simply become a fleeting experience.

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