Manta ray, the filter feeder

As manta rays are now protected internationally by the CITES convention, trade will now be controlled to ensure the long-term survival of these majestic creatures.

Mantas are threatened due to demand for their gill plates. In this blog post, we’ll find out what gill plates are, their function and why they are prized by the Chinese medicine trade.

Manta Feeding with gill rakers

Filter feeders and plankton

Whilst the vast majority of sharks and rays are predatory, some such as the Basking Shark, the Whale Shark and the Manta Ray, have adopted a more placid “grazing” lifestyle.

Despite being amongst the largest marine species, these animals feed by straining and eating plankton from the surrounding water. The name “plankton” is derived from the ancient Greek planktos meaning “wanderer” or “drifter”.

Plankton is used to describe many different groups of bacteria, plants and animals.Some are small and invisible to the eye; others are larger, like shrimps. Some drift up and down in the water column, whilst others drift horizontally with the current.

Together they form an important source of food for mantas and many other marine animals.

How does filter feeding work?

Mantas have modified gills which allow them to filter plankton from the water column.

When it is time to feed, the manta opens its mouths, unrolls its cephalic fins and channels plankton rich water into its mouth. Any plankton flowing over the gill plates that are large enough to be trapped will be sieved out, pushed to the back of the throat and ingested.

The distribution of plankton is not uniform across the world’s oceans, and there are hotspots where the plankton concentration is particularly high.

How do mantas behave when feeding?

Behaviourally, mantas have adopted numerous ways of feeding and foraging.

One of their more spectacular manoeuvres is “barrel rolling”, where they gracefully somersault backwards, over and over again. Sometimes, large numbers of mantas can be seen congregating in one area, swirling and somersaulting in their hundreds.

Mantas often form feeding chains, whereby they swim one behind another, and at other times they will feed from the seabed, scooping up plankton that have sunk to the sea floor.

A manta ray feeding chain
A manta ray feeding chain

Why are gill rakers sought after?

It is traditionally believed in Chinese medicine that gill rakers are beneficial in the treatment of many diseases, including asthma, skin rashes, chicken pox, and even cancer.

There is no scientifically proven health benefit associated with the consumption of manta ray gill plates. Now that manta trade is being closely controlled, permits will only be granted if there is no detrimental impact on the survival of manta rays in the wild.

You can do your part in saving manta rays by not purchasing any gill rakers.

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