Until recently, trawler fishermen did not know how their method of fishing worked. Many assumed?
Until recently, trawler fishermen did not know how their method of fishing worked. Many assumed that the nets acted as an enormous sieve in catching the fish But recent experiments carried out by the Marine Laboratory at Aberdeen, Scotland, show the method to be right but the theory wrong.
With a battery of instruments attached to the nets and divers observing, scientists were able to determine just how the nets work. The test showed that fish actually help catch themselves. Herded together along the net's tow-line, the fish swim along inside the net without trying to escape through the wide mesh. Eventually tiring, they fall back into the narrow mesh and are trapped.
The experiments carried out at Marine Laboratory were designed to measure the speed of various species of fish. The results of the tests may provide trawler skippers with a full set of tables giving the speed and length of run of their intended catch.
SYNOPSIS: As the net was toward along behind the ship, the specially designed instruments gave readings on depth, direction of movement, speed and strain. They did find out how the net worked ... and that the fish actually help catch themselves. Herding together along the net's tow-rope, many of the fish swim along inside the net without trying to escape. Eventually tiring, they fall back and are trapped in the net. The problem, then, was to determine the right speed for the trawler in order to maximise the catch.
The researchers took some of their catch back to the laboratory. There, under the watchful eye of closed circuit television, the fish were put through their paces. The fish were trained to respond to a light signal at both ends of the tank. Food was the leeward for the response, and the fish raced for it.
The experiment showed that all fish have a low cruising speed, which they can maintain indefinitely. But at high speed, all fish become exhausted in a few minutes.
The larger the fish .. the faster and longer it can swim. When the experiments are completed, trawler skippers may have a full set of tables giving speed and length of run specifications for individual species.