What are the causes of overfishing?

There are a number of causes to the worldwide problem of overfishing. A large problem is that oceans are beginning to run out of fish. So, fishing companies are beginning to travel to more distant areas to catch more fish. In time, all the oceans may be depleted of fish. Also, the needs for fish are beginning to grow. For example, the producers of certain fish, such as tuna, are starting to change the way they produce their products. This adds more diversity and perhaps a better taste to their tuna. Because of this, the consumption of tuna is beginning to grow, leading to the need of more fish, which eventually leads to overfishing. People are creating new fishing
techniques, as well as using new technology, to help them catch more fish than before.

The photo to the above depicts the global issue that which is overfishing.

Source:
http://www.greenpeace.org/australia/issues/overfishing/overview/causes

Source of picture:

http://www.sea-way.org/blog/Overfishing01.JPG