My Science School

               There is perhaps no human activity older, more varied or stranger, than fishing. He tricks and catches fish in different ways, such as using his bare hand, or fishing even with harpoon guns in whaling! But the method most used today is the one by which it produces the biggest share of commercial fishing known as trawling. Do you know how do trawlers fish?

               Trawlers fish with a bag-size net. It is let out on long warps or ropes. The fish are swept in at the wide, open end and then get trapped at the narrower, closed end. The trawler may be between 100 to 1500 metres long or more. In this system, the motorized fishing boats trawl by towing a large net in three different ways to keep the mouth of the net open. Firstly, a beam can be placed across the head of the net; secondly a pair of boats can be used - one at each side of the net to tow it and thirdly, some floating weights, called otter boards can be attached to the sides of the mouth of the net.

               However, the beam trawl is only used on a few small fishing crafts, and on the other hand, pair trawling is used to catch fishes from the bottom of the sea to enormous depths, sometimes at the range of 1500 metres or more. When the net is full, powered winches haul it on the board through a ramp. The otter trawl is widely used and is employed on almost every fishing technique except the smaller trawlers.

               The net gathers in everything including eggs, newly hatched fishes and algae. But this system is considered to be very destructive and alarming in the context of overfishing along the seas. Sometimes an entire fleet of fishing vessels is headed by a large factory ship fitted out just for processing of the catch. A single “sweep” of the net often taken in terms of tonnes of fish provides an idea of the quantity of fish caught in rich seas. Deep sea fishes like sardines and herrings together account for eighteen percent of the world’s catch.

               Today, the large motor fishing vessels are fitted with sonar or echo-sound equipments to locate a shoal of fish.