| Today we're going to look at one of my favourite fish - |
| the shark. |
| As you know, sharks have a reputation for being very dangerous creatures |
| capable of injuring or killing humans, |
| and I'd like to talk about sharks in Australia. |
| Sharks are rather large fish, |
| often growing to over 10 metres |
| and the longest sharks caught in Australia have reached sixteen metres. |
| Sharks vary in weight with size and breed, of course, |
| but the heaviest shark caught in Australia was a White Pointer - |
| that weighed 795 kilograms - |
| quite a size! |
| Sharks have a different structure to most fish: |
| instead of a skeleton made of bone, |
| they have a tough elastic skeleton of cartilage. |
| Unlike bone, this firm, pliable material is rather like your nose, |
| and allows the shark to bend easily as it swims. |
| The shark's skin isn't covered with scales, like other fish, |
| instead, the skin's covered with barbs, giving it a rough texture like sandpaper. |
| As you know, sharks are very quick swimmers. |
| This is made possible by their fins, |
| one set at the side and another set underneath the body, |
| and the tail also helps the shark move forward quickly. |
| Unlike other fish, |
| sharks have to keep swimming if they want to stay at a particular depth, |
| and they rarely swim at the surface. |
| Mostly, they swim at the bottom of the ocean, |
| scavenging and picking up food that's lying on the ocean floor. |
| While most other animals, including fish, hunt their prey by means of their eyesight, |
| sharks hunt essentially by smell. |
| They have a very acute sense of smell - |
| and can sense the presence of food long before they can see it. |
| In Australia, where people spend a lot of time at the beach, |
| the government has realised that it must prevent sharks from swimming near its beaches. |
| As a result, they've introduced a beach-netting program. |
| Beach-netting, or meshing, involves setting large nets parallel to the shore; |
| this means that the nets on New South Wales beaches are set on one day, |
| and then lifted and taken out to sea on the next day. |
| When shark-netting first began in 1939, |
| only the Sydney metropolitan beaches were meshed - |
| these beaches were chosen because beaches near the city are usually the most crowded with swimmers. |
| Ten years later, in 1949, |
| systematic meshing was extended to include the beaches to the south of Sydney. |
| As a result of the general success of the program in Sydney, |
| shark-meshing was introduced to the state of Queensland around 1970. |
| The New Zealand authorities also looked at it, |
| but considered meshing uneconomical - as did Tahiti in the Pacific. |
| At around the same time, South Africa introduced meshing to some of its most popular swimming beaches. |
| When meshing began, approximately 1500 sharks were caught in the first year. |
| However, this declined in the years that followed, |
| and since that time, the average annual catch has been only about 150 a year. |
| The majority of sharks are caught during the warmest months, from November to February, |
| when sharks are most active |
| and when both the air and the ocean are at their maximum temperature. |
| Despite quite large catches, |
| some people believe that shark meshing is not the best way to catch sharks. |
| It's not that they think sharks are afraid of nets, or because they eat holes in them, |
| because neither of these is true. |
| But meshing does appear to be less effective than some other methods, |
| especially when there are big seas with high rolling waves and strong currents |
| and anything that lets the sand move - |
| the sand that's holding the nets down. |
| When this moves the nets will also become less effective. |