Thornback Ray

A Thornback Ray being kept in the backroom tanks at London Aquarium.

The Thornback Ray is one of the most common rays in the world, encompassing a large area of the world, from Europe to South Africa, where it lives in shallow seas. Many are kept in the ray pools at the London Aquarium, where I spent a day as a Marine Biologist, including the Thornback Ray that I discovered there. You can recognise the Thornback Rays by the spiny ridges that run down their body from the middle of their back to the end of their tail. In terms of colouration, most rays have a number of pale spots on their backs, although the adolescent pictured above in more a matt brown colour. Females often develop spikes on the underside of their body as they grow older, and this is an easy way to sex the ray. Most rays measure at about 3/4 of a metre, although they have been known to reach lengths of just over 1 metre.

The Thornback Ray lives and feeds in the seabed, where it hunts down crustaceans like shrimp and crab, molluscs like sea snails and small fish which hide in the sand, which it grinds up with its plate like teeth. The camouflage on its back means that the ray is almost perfectly disguised from predators when it buries in the sand. Most sea animals have far less developed eyes than humans, and have to rely on other senses to find them. In order to find food themselves, the rays can sense the movement of sea creatures below the sand by the electric signals they produce,  allowing them to catch their prey even though they cannot see the sandy sea floor.

Many of these rays are caught every year by fishing trawlers, and passed off as skate for the fishing market. This repeated overfishing has left them in a near endangered state, so next time you order skate at a fish and chip shop, remember it could be a Thornback Ray instead.

I find rays to be really interesting animals, utterly different from any other creature in the world. I hope to come into contact with other types of ray in the future, perhaps some of the open water rays.

Kenneth or Kinsley

I triumphantly display a captured mermaid's purse.

Of all my experiences at the London Aquarium on my Marine Biologist for a Day trip, the absolute best was when I helped recover and candle mermaid’s purses from the ray pool. Rays and Dogfish keep their young in little cocooned capsule-like eggs that people often call mermaid’s purses, due to their appearance as a little pouch. While not all ray eggs are shaped like this, some being rounder or corkscrew shaped, these are the iconic ray eggs, and they are the type made by the rays at London Aquarium. In the ray pool you can find Undulated and Thornback Rays, who are on a breeding program to help preserve both species, in particular the Undulated Ray. I was sent into the exhibit armed with nothing but a net and my eagle-vision, to spot and recover the eggs. I went around the perimeter, scooping up any within nets reach, and with the help of the public, I managed to spot 18 eggs in total, a tidy sum. The purses further into the middle of the pool, out of net reach, would be collected later that night using a pair of waders to reach in inner pool.I search in vain to locate an egg with a live ray inside.

I brought my hard earned clutch of ray eggs back to the laboratory in London Aquarium, in order to identify and candle the eggs. The eggs of Thornback and Undulated Rays are very similar, both taking the purse like shape, but with the use of a chart, I was able to identify the different eggs. While the undulated eggs had smoother smaller sides with straight points on each corner, the thornbacks had more jagged edges with wavy points on the corners. All but one of the eggs were thornback, a testament to the necessity to help these Undulated Rays breed, before they begin to run thin in the wild. Even then, most ray eggs do not contain live animals, instead merely being empty cases filled with water and yolky sludge. I held the eggs up to a light, which shone through the translucent casing and revealed the contents to me, in a technique called ‘candling’. Nothing. Nothing again. Very little but water in any of the eggs. It is very rare for the aquarium to find live eggs, and I was reassured that this was normal, rather than just exceedingly bad luck. However, as I approached the last few eggs, my luck became fantastic, as I candled an egg to reveal a tiny thornback living inside, only a few weeks into growth. It was the most wonderful feeling I’ve ever had, discovering new life inside the tiny egg, and by the tradition of the aquarium I was allowed to name them. Kenneth if they were a boy, or Kinsley for a girl. They were the first live ray to have been laid for 7 months, and all of the staff were very excited. I was very excited. We took Kenneth/Kinsley and laid them in the egg pool, with the other unhatched mermaid’s purses.I reveal Kenneth or Kinsley for all the world to see.

I cannot truly describe how amazing it felt to find the baby ray in its egg; it was probably the most fantastic and proudest moment of my life so far. The egg will take 9 months to mature and hatch, and I will return again to the aquarium in order to see my baby ray amongst all of the others.

Feeding the Ray Pool

I feed the juvenile tank in the aquarium ray pool.

On my day as a helper at the London Aquarium, one of the interesting activities I participated in was feeding the ray pools, which are the open pools near the start of the aquarium containing all manner of flatfish, crabs and rays. Taking a delectable tray of calamari, raw fish, freeze dried prawns and other seafood goodies, the staff, Monica (my guide for the day), and I went about the pools making sure all of the animals were fed. Under the direction of the staff I selected the correct creatures and gave them food with the use of a long stick and some well timed throws.

Above I am feeding the juvenile tank, where the adolescent rays are kept after they are old enough to come out of the private tanks in the back of the aquarium. There are a selection of Undulated and Thornback Rays in the ray pools, and we used smaller pieces of fish and squid for these younger ones. In the wild they would act the same way any adult ray did, but for the sake of safety the aquarium places them separate to the larger crabs of the adult pool. The more confident rays came to the surface to receive their food, and would often snatch food away from the shyer animals, meaning I had to make sure those rays got food while the others weren’t looking. It was difficult to time, since they did not always eat the food immediately, but between myself and the staff, every ray got some food.The aquarium staff feed the various denizens of the ray pool.

In the larger ray pool, there were some animals other than rays to feed, such as the aptly named Herbert, who was a Turbot, and a large slow moving Edible Crab. Turbots camouflage is perfect for the sandy sea bed, a mixture of pale yellows and white, only identifiable by the twin eyes poking out from under the sand. Flatfishes eyes start on different sides of their heads when they are born, but as they develop, the eye on the bottom side rise through the head to the other side, since they do not see on the face down side. The crab was slow to move, and I had to dangle the squid and prawns in front of his face before he would try to eat them. Fighting back other hungry rays, I would hold it in front of him, waiting for his soporific claw to close around the food.

It was incredible fun to feed these animals, and I was amazed to be working so closely with such  incredible creatures. I hope to work with animals like this again in the future, and recommend it utterly to all who are considering such opportunities.