1Today we're going to look at one of my favourite fish -
2the shark.
3As you know, sharks have a reputation for being very dangerous creatures
4capable of injuring or killing humans,
5and I'd like to talk about sharks in Australia.
6Sharks are rather large fish,
7often growing to over 10 metres
8and the longest sharks caught in Australia have reached sixteen metres.
9Sharks vary in weight with size and breed, of course,
10but the heaviest shark caught in Australia was a White Pointer -
11that weighed 795 kilograms -
12quite a size!
13Sharks have a different structure to most fish:
14instead of a skeleton made of bone,
15they have a tough elastic skeleton of cartilage.
16Unlike bone, this firm, pliable material is rather like your nose,
17and allows the shark to bend easily as it swims.
18The shark's skin isn't covered with scales, like other fish,
19instead, the skin's covered with barbs, giving it a rough texture like sandpaper.
20As you know, sharks are very quick swimmers.
21This is made possible by their fins,
22one set at the side and another set underneath the body,
23and the tail also helps the shark move forward quickly.
24Unlike other fish,
25sharks have to keep swimming if they want to stay at a particular depth,
26and they rarely swim at the surface.
27Mostly, they swim at the bottom of the ocean,
28scavenging and picking up food that's lying on the ocean floor.
29While most other animals, including fish, hunt their prey by means of their eyesight,
30sharks hunt essentially by smell.
31They have a very acute sense of smell -
32and can sense the presence of food long before they can see it.
33In Australia, where people spend a lot of time at the beach,
34the government has realised that it must prevent sharks from swimming near its beaches.
35As a result, they've introduced a beach-netting program.
36Beach-netting, or meshing, involves setting large nets parallel to the shore;
37this means that the nets on New South Wales beaches are set on one day,
38and then lifted and taken out to sea on the next day.
39When shark-netting first began in 1939,
40only the Sydney metropolitan beaches were meshed -
41these beaches were chosen because beaches near the city are usually the most crowded with swimmers.
42Ten years later, in 1949,
43systematic meshing was extended to include the beaches to the south of Sydney.
44As a result of the general success of the program in Sydney,
45shark-meshing was introduced to the state of Queensland around 1970.
46The New Zealand authorities also looked at it,
47but considered meshing uneconomical - as did Tahiti in the Pacific.
48At around the same time, South Africa introduced meshing to some of its most popular swimming beaches.
49When meshing began, approximately 1500 sharks were caught in the first year.
50However, this declined in the years that followed,
51and since that time, the average annual catch has been only about 150 a year.
52The majority of sharks are caught during the warmest months, from November to February,
53when sharks are most active
54and when both the air and the ocean are at their maximum temperature.
55Despite quite large catches,
56some people believe that shark meshing is not the best way to catch sharks.
57It's not that they think sharks are afraid of nets, or because they eat holes in them,
58because neither of these is true.
59But meshing does appear to be less effective than some other methods,
60especially when there are big seas with high rolling waves and strong currents
61and anything that lets the sand move -
62the sand that's holding the nets down.
63When this moves the nets will also become less effective.