Conservation through Research, Awareness and Education

UK Registered Charity Number: 1145387

Manta Fisheries

At the fish markets in Sri Lanka piles of spine-tail mobula rays are offloaded onto the docks on a regular basis.

In general, the flesh of all sharks and rays is not considered as good to eat as that of the bony fishes; such as cod, herring, tuna, groupers, billfishes, etc. As a result, commercial and artisanal fishermen have mostly avoided fishing for these cartilaginous animals in the past centuries, instead concentrating their efforts to fish for the ‘tastiest’ species in our oceans.

However, as stocks of our sea’s most plentiful and desirable species have become dramatically depleted, fishermen and nations have turned their nets and hooks on new targets, marketing and exploiting their way through the food chain from one species to another in the hunt for profits. Unfortunately for the manta rays and their relatives their turn has now come…

Fishing for Giants

This giant oceanic manta ray was fished in Mexico's Sea of Cortez; the choicest meat removed from its pectoral fins, while the rest of the animals will be used as bait or discarded.

In many parts of the world, coastal communities have turned from the occasional artisanal consumption of these animals for food, to commercial fisheries for their flesh, and more recently, to sell their dried branchial gill filaments (plates) as an increasingly sought after ingredient in some Chinese medicines (see our Gill Plate Trade page). It is often a sad fact of human nature that the more endangered a wild animal becomes, the greater our desire to posses or consume it. Diminishing stocks drive a lucrative trade (often illegal) for those prepared to take on the increasing costs and risks required to hunt down, trade in, and consume the dwindling populations of these endangered species.

Harpooned mobula rays line the beach in Mexico's Sea of Cortez, while another ray leaps clear of the water in a desperate attempt to break free of the harpoon impaled into its back by fishermen.

Among the first countries to commercially fish their manta population was Mexico, when in the early 1980’s fishermen in the Sea of Cortez switched from subsistence and bycatch fishing of the locally abundant oceanic manta and mobula ray species to a directed target fishery. Using harpoons to impale the surface feeding animals, and gill nets to entangle and drown them, the rays were easy targets and their numbers soon began to plummet. The giant carcasses were towed back to the beaches where only the choicest flesh was sold for consumption, while the remainder was often used as bait in lobster pots, or simply discarded. Within just a decade the manta ray population within the Sea of Cortez was virtually wiped out and the fishery collapsed. It was not until 2007 that the Mexican Government finally passed legislation protecting the manta and mobula rays in Mexican waters, but by then the damage had already been done. Even today, after over a decades since the fisheries collapsed, virtually no mantas are recorded in this area and those that are still fall victim to illegal fishing, or bycatch.

This oceanic manta ray dwarfs the fishermen as they drag their catch into the beach. This ray was probably caught in nets set further offshore.

Many other countries have also targeted their manta and mobula ray populations with similar results, switching from a local artisanal fishery to a commercial export fishery wherever a market for their products can be found. The Philippines, Indonesia, Mozambique, Madagascar, India, Pakistan, Sri Lanka, Brazil and Tanzania have all followed Mexico’s lead, with similar trends of population declines reported in many of these countries where data exists. Yet out of all these countries, only in the Philippines are there now official laws in place to protect these vulnerable species.

This giant oceanic manta was harpooned off the mouth of the Rio Grande by trophy hunter fishermen in June 1935.

While manta and mobula rays are mostly caught today for their gill plates and the local consumption of their meat, other parts of these mobulid rays were also, although less commonly, utilised. Their skin, similar to leather, was sometimes used as the canvass on drums in the Maldives, while their livers, from which rich oils were extracted, were used to waterproof and seal the hulls of traditional fishing vessels before more effective commercial products became available. In the past, American and European trophy hunters also considered ‘Giant Devil Rays’ good hunting, with many of these ‘Sport’ fishermen snapped posing in front of their catch. These rays are especially easy to catch for fishermen and trophy hunters alike; relatively slow swimmers they have a tendency to be found feeding or basking at the water’s surface, easy targets for anyone with a harpoon or net.

Why So Vulnerable?

In the past, wherever active targeting of manta and mobula rays has occurred, these fisheries have quickly collapsed. The reason for these rapid declines is simple; manta rays live for a long time and reproduce infrequently. They are large animals with few natural predators that have long gestation periods which result in the birth of just a single pup (most of the time), which themselves take several decades to reach sexual maturity. As a result of this life history strategy and like most other large marine animals, manta ray populations simply cannot survive, or sustain, any commercial fisheries for long. Any target fishery which annually removes even a relatively small percentage of the breeding adults results in a rapid decline in the overall population within just a few years, as the remaining mature individuals simply cannot breed fast enough to replace the loses. And this is why, even with complete protection from anthropogenic threats, an overfished population of manta rays will take decades to recover to its natural state. A situation which, in the realities of today’s global fisheries management and protective enforcement (or lack thereof), this is never likely to happen to these populations which have already been overfished.

Eating Giants

Fresh mobula meat is sliced into strips in Sri Lanka and sold at the local markets.

In Sri Lanka, the majority of manta and mobula meat is processed and sold as 'dry fish'. The ray's pectoral fins are sliced into strips before being salted and dried for several days.

While the huge size of manta rays means each of these animals yield a lot of meat, most communities avoided catching them in the past due to their propensity to entangle or damage fishing nets, which can prove to be very costly. In addition to this, manta meat is not commercially viable simply because it does not taste very good and quickly spoils. The meat (consisting of wings and the posterior part of the body) of manta rays is said to have a texture considered too “grainy” or “sandy” for commercial consumption and is generally dried and sold as low quality dried fish to be used as animal feed (chicken and shrimp farms). The meat from mobula rays on the other hand is more valuable than manta meat and is commonly consumed when fresh (only by local communities), but is still at least 50% less valuable than the lowest quality tuna.

In recent years however, with the increased demand for the dried gill plates, the fishing of these species has significantly increased. These cartilage filaments that filter plankton from the water are by far the most valuable part of the ray, with each kilo of gill raker being worth over 100 times the price of a kilo of the meat. As word spreads within the fishing communities of the value of these gills and as the wealth of China’s population (the primary consumers of gill plates) continues to grow, the pressures on the remaining populations of these rays is rapidly escalating.

On the tiny island of Lamelera in Indonesia the local islanders specialise in fishing the large pelagic animals which frequent the deep oceanic waters surrounding their island. This oceanic manta has been harpooned from the surface before being killed with a cut to the brain.

In regions that previously ignored their mobulid rays, releasing any animals that became entangled in their nets, these entangled rays are now retained, killed and brought aboard the fishing vessel for sale. This new demand for plates, coupled with the depletion of more traditionally desirable fish stocks (i.e. sharks, tunas and billfishes), provides ample incentive for more and more fishermen to diversify into the manta and mobula ray fishery. From a fisheries perspective mantas and their close relatives can now be categorised as targeted by-catch. Such fisheries are known to exist in the Philippines, Indonesia, Thailand, Tonga, India, Sri Lanka, Mexico, Peru, and several locations in Africa, including Mozambique, Ghana, Tanzania, Madagascar and Somalia. While there is evidence of fisheries in these countries, a lack of scientific data makes it difficult to quantify their actual extent and true impact.

Manta rays are usually too large to land on the fishing boats whole, so the rays, often still alive, are sliced into sections in the sea before being hauled onboard.

These increases in fishing demand, along with the continued advancements in fishing technology (such as bigger and faster boats, bigger and stronger nets, the usage of satellite telemetry to predict locations of high productivity, etc), means that the number of rays being caught is likely to be rising. It is therefore imperative that further field studies are carried out around the world to quantify the extent and impact of these fishery’s in order to ensure the preservation of manta and mobula ray species and populations worldwide. What is increasingly becoming clear though is that both regionally and globally all mobulid rays are currently heading into an uncertain future, facing the imminent threat of extinction without rapid intervention, it may be too late to save these incredible species if we do not act now.

© 2017 Manta Trust