As is vividly/symbolically shown/described/depicted/illustrated/revealed/portrayed in the cartoons/drawings/portrayals/photos/photographs/pictures, with the rapid/speedy social and economic development, the number of fishes has sharply decreased. In one picture, there were various kinds of fish and only one fishing-boat in 1900. On the contrary, in 1995 there was only one fish, but many fishing-boats.
The purpose of this picture/cartoonist is to show us that due attention has to be paid to the decline of ocean resources. Owing/Due to over-fishing, the number of fishes has obviously shrunk. If we let this situation go/continue as it is, we do not know where fish will be in the near/forthcoming future. By that time, our environment will suffer a great destruction.
Therefore/Hence/Accordingly, it is imperative/necessary for us to take drastic/effective/some measures/steps/actions. For one thing, we should appeal to our governments/authorities to make/legislate/enact/issue strict laws and regulations to control/regulate commercial fishing. For another, we should enhance/cultivate/increase the awareness/sense of people that the ocean resources are significant/vital/essential/crucial to us. Only in this way/by doing so can we protect our ocean resources. Also, I assume/maintain/reckon that we humans can overcome/surmount this difficulty, and we will have a brighter/more brilliant future.