Smart dolphins, scary sharks and cute polar bears ...... are the star animals in the oceanarium. But a lot of what you know about them as common knowledge is wrong.

　　Nowadays, many people like to go to the Oceanarium to observe marine animals, and a marine science exploration activity held by the Chaoyang District Science and Technology Association of Beijing at the Beijing Oceanarium recently aroused a lot of interest. The professional teachers' interesting science stories provided a sumptuous science and technology meal, but it was only through the teachers' explanations that many people realised that their perceptions of many of the oceanarium's star animals were still very misconceived.

     For many years, there have been stories and legends circulating everywhere about dolphins saving people from falling into the water on the ocean, but in fact these stories and legends have been given good intentions by humans. In reality, dolphins do not know how to save people in the true sense of the word, it is more of an instinctive reaction.

　　It turns out that as mammals in the sea dolphins do not breathe with their gills like fish, but with their lungs. Therefore, dolphins cannot survive under the sea for as long as fish can, and they need to surface every so often to adjust their breathing. Being able to surface to breathe is a skill that dolphins must master in order to survive, and newborn dolphins can only survive if they have mastered this method of breathing.

　　Therefore, in order to enable the dolphins to learn how to breathe as soon as possible, their mothers will lift them above the surface in their own unique way after birth, so that they can learn how to breathe as soon as possible. Sometimes, when someone accidentally falls into the water, the mother dolphin will mistake it for her baby and so will rescue it without reservation. And they warn animals that want to intrude to prevent them from approaching the person in the water. It is for this reason that dolphins sometimes rescue people who fall into the water by mistake. But this behaviour of dolphins is often mistaken by many people as them actually knowing how to save people.

     Many regular visitors to the oceanarium notice that sharks swim slowly but almost all the time, and always with their mouths open. This is true, some species of shark simply cannot stop or face death, mainly because many of the organs of these sharks have evolved to be able to catch prey quickly in the ocean, fresh water flows through the gills so efficiently that the function of active water intake for breathing has been lost, while the gills have also degenerated. These sharks also tend to have a high metabolic rate, and in order to obtain the oxygen dissolved in the water These sharks also tend to have high metabolic rates and must swim constantly in order to obtain the oxygen dissolved in the water. These sharks have a high metabolic rate and must swim constantly to obtain the oxygen dissolved in the water. They breathe by 'banging' the water through their gill slits (the fissures at the back of the shark's mouth) and would suffocate at rest.

　　But not all sharks are like this. A large number of shark species have evolved to retain oral suction breathing, which means that they can actively inhale and breathe, just like other fish, such as nurse sharks, angel sharks and baleen sharks, which can stay motionless on the sea bed for long periods of time. It is only because some of the stars of the shark species, such as great whites and whale sharks, need to breathe by swimming constantly that many people mistakenly believe that all sharks are like this.

    Zoologists have observed that some marine animals such as sea lions and seals and fur seals enjoy swallowing small smooth pebbles and beach stones. The beach stones they swallow are generally about the size of a golf ball, but there are exceptions, such as a large stone weighing about 11 kg that was once found in the stomach of a sea lion.

　　Why do these marine animals swallow rocks? Some believe that they swallow rocks in order to increase their body weight and facilitate diving, as rocks can act to reduce their fatty buoyancy. However, there are many biologists who disagree, arguing that the stones are used to grind up food, just like the sand in a bird's mouth, to aid digestion. Others believe that the stones are used to knock out parasites such as nematodes and tapeworms from the stomach, and that when the parasites are ground to death, they are vomited back up by the stomach.

　　Dr Tom Locklin of the National Marine Mammal Laboratory in Seattle, Washington, USA, suggests that there may be another reason why sea animals such as sea lions swallow rocks: they are forced to fast during the reproductive season when they cannot leave their hatching grounds for up to two months in order to breed their offspring. If the rocks were filled in the stomach, it would create a feeling of fullness in the stomach during this difficult period to alleviate the torment of hunger. However, scientists have found a considerable amount of stones in the stomachs of these young, still breast-fed sea animals, which makes the above theory difficult to justify.

　　In other words, scientists have yet to find a convincing answer as to why sea lions, seals, fur seals and other marine animals swallow rocks, and further research by marine zoologists is needed.