One of the largest animals kept at the London Aquarium are the two Sand Tiger Sharks, or Grey Nurse Sharks. On my Marine Biologist Day at the aquarium I was asked to help prepare some fishy food for them, since they were feeling poorly that day. In the ocean, the sharks live in saline water that contains a number of essential chemicals that they need to keep their bodies running, in particular iodine. London Aquarium is not on the coast so they can’t bring in water from the sea, like Brighton or Plymouth Aquarium, to use in the tanks. Instead the have to create their own saline solution by salting the tank water themselves. While they are able to keep the water at the correct salt levels, it is difficult and impractical to keep the correct balance of other chemicals, and so these chemicals are added to the food they eat.
If a shark lacks iodine, like a human, they will begin to develop goitres (large inflamed lumps) around their throat and near the base of their fins. This is very dangerous for them, so I had to put together 60 iodine tablets, by pouring the white powder into small transparent casings. While I did this, Monica was cutting slots in the side of the fish we would feed to the sharks, where we would push in the pills. After I had made all 60, I began to stuff an iodine pill and a large pink vitamin pill into each of the smaller fish. The larger fish received 2 iodine and pink tablets.
Sand Tiger Sharks, or Carcharius Taurus, is neither related to the tiger, nurse or sand shark, despite it’s myriad of confusing names, such as Grey Nurse Shark, or Blue-Nurse Sand Tiger. Even it’s scientific name translates to bull shark, which it is also not related to. They are fairly relaxed and gentle sharks, and respond very well to being kept in captivity, which makes them one of the easiest sharks to keep. Many aquariums use them not only because they are so easy to keep, but because they are so fearsome looking, being roughly 2 to 3 metres long with large bodies and sharp heads. The teeth are pointy and lack serration, which most other sharks possess, and they swim with their mouths open, making them seem very scary for visitors to the aquarium. They are seen around most warm waters in the world, at the edges of continents, avoiding the open ocean. The Mediterranean, east coast of America, Australia and most of Africa house them, where they can be found living in sandy shallows, all the way to the edge of the continental shelf.
These sharks are ambush predators in the wild, leaving their shelter at night in order to hunt large fish, rays and even smaller sharks. They have been known to catch fish up to half of their size, which they eat in a few bites. The animals they catch are mainly bottom feeders that live on the sandy sea floor, and they will wait quietly for them to come past. The Sand Tiger Shark has a devious trick in order to remain quiet in the water, in which it rises to the surface and gulps air into its stomach. Like a diver, this air is used to maintain a neutral buoyancy so that they have to move very little in order to swim. This means they can get close to fish while barely making a sound, giving them a big advantage while hunting.
It is good that the Aquarium is keeping these animals, since they are on the endangered protection list, and have one of the slowest reproduction rates of any shark. After Monica and I had finished the fish, Pete, another staff member took them away to be fed to the sharks later.