Land prices are rising too, forcing change in economic activity and forcing out local fishing villagers. World fish catches peaked in 1987 and are now falling. Because modern fishing techniques suck up too many fish, large and small so there are not enough young fish left to breed. In Asia . Fish farms are dangerous in themselves because diseases spread from the farmed fish and affedt the wild fish.
Coral reefs are like the rainforests of the sea, supporting many fish.
This slogan made Greenpeace, an international environmental organisation, famous, and it still applies. Whales, dolphins and many big sea mammals have been hunted to the point of extinction. Most countries use the sea as a sewer. For example, coastal cities in Africa dump hundreds of millions of litres of sewage and industrial waste into the sea a year. This will continue as they cannot afford sewage treatment plants.