Fishing in the North Sea is concentrated in the southern part of the coastal waters. The main method of fishing is trawling.[citation needed]
Annual catches grew each year until the 1980s, when a high point of more than 3 million metric tons (3.3 million S/T) was reached. Since then, the numbers have fallen back to around 2.3 million tons (2.5 million S/T) annually with considerable differences between years. Besides the fish caught, it is estimated that 150,000 metric tons (165,000 S/T) of unmarketable by-catch are caught and around 85,000 metric tons (94,000 S/T) of dead and injured invertebrates.[1]
Of the caught fish, about half are used for the production of fish oil and fish meal.[citation needed]