The increased fishing pressure and the competition amongst fishing nations and their fleets severely stresses fish stocks and the marine environment. The widespread use of unselective fishing gear and indiscriminate practices result in one-quarter of the all the fish brought on board fishing vessels each year being discarded, usually dead or dying, back to the sea. Commercial fishing vessels throw back on average about 27 million tons of unwanted fish annually. That amounts to about half of all the fish caught from the oceans each year that are consumed directly by humans. Along with these, millions of other marine animals are being incidentally captured and killed in fishing operations.
Some fishing gear is particularly deadly for certain animals in some situations.
Longline fishing boats kill many tens of thousands of albatross each year in southern hemisphere oceans. Driftnets indiscriminately killed millions of marine creatures, while targetting for just one or two commercially valuable species. Marine mammals are frequently killed in great numbers in trawls, set nets and purse seine nets. In addition there is severe damage caused by fishing operations that use destructive gear and fishing practices, like bottom trawling, that physically disturbs marine habitats such as the ocean floor, sea grass beds or coral reefs. The bulk of the problems stem from twenty fishing countries whose fleets land 80 percent of the total marine catch worldwide.