Food z'n Abundanæ
35
screen in a complete picture of the sector. This visual display lacks
the detail that a hunter on land might require but it does represent a
considerable advance. During experimental trials the equipment
showed sh moving about the cooling water intake of a power
station, and individual sh could be seen and followed. Other
experiments have shown that the echoes from different sh may
vary according to the frequency of the signal and the species. Thus
scanners can be developed which will inform the skipper of the
presence of sh and, further, the species.
Professor Tucker’s group is not the only one concerned with
providing underwater ‘eyes’. For example a system known as
‘Bifocal’ has been developed at the British Admiralty Research
Laboratory. This system, which gets its name from an ability to
switch from scanning a wide area to examining a small sector within
it, has been used to study the movements of a trawl being towed
through the sea. Several commercial companies are also involved in
improving present sh detectors and are devising new ones. How—
ever, sonar still has a long way to go before it graduates as the perfect
sh detector. Even with the present devices, the catch may bear little
relationship to the sonar evidence. One reason for this discrepancy
is that one can never be sure that the shing net will move through
the same path as that surveyed by the sh detector. Another is the
effect of the skipper’s skill and experience in using the data provided
by the instruments.
Just as the basic reliance on the skipper has not been seriously
eroded, so the major shing industries continue to depend on
methods which in many respects have changed very little possibly
for centuries and certainly for decades.
One of the oldest organized sheries is that for herring—records
of an English herring shery go back to Saxon times. The principal
gear used in herring sheries is a gill net known as a drift net. This
net, made up of sections some 50 yards long and 10 yards deep, may
extend for three miles or so. The top corners of each section hang
from large oats while the rest of the net’s top, which is about six
feet below the surface, is buoyed up with a line of corks. A heavy
cable or warp holds down the bottom. Stretching like some giant
tennis net, it is towed gently along by the shing boat drifting with
the wind. During the night the herring move into the surface waters
to feast on the plankton there. When they meet the net barrier, they
try to swim through but the mesh is so gauged that only small fish
35
screen in a complete picture of the sector. This visual display lacks
the detail that a hunter on land might require but it does represent a
considerable advance. During experimental trials the equipment
showed sh moving about the cooling water intake of a power
station, and individual sh could be seen and followed. Other
experiments have shown that the echoes from different sh may
vary according to the frequency of the signal and the species. Thus
scanners can be developed which will inform the skipper of the
presence of sh and, further, the species.
Professor Tucker’s group is not the only one concerned with
providing underwater ‘eyes’. For example a system known as
‘Bifocal’ has been developed at the British Admiralty Research
Laboratory. This system, which gets its name from an ability to
switch from scanning a wide area to examining a small sector within
it, has been used to study the movements of a trawl being towed
through the sea. Several commercial companies are also involved in
improving present sh detectors and are devising new ones. How—
ever, sonar still has a long way to go before it graduates as the perfect
sh detector. Even with the present devices, the catch may bear little
relationship to the sonar evidence. One reason for this discrepancy
is that one can never be sure that the shing net will move through
the same path as that surveyed by the sh detector. Another is the
effect of the skipper’s skill and experience in using the data provided
by the instruments.
Just as the basic reliance on the skipper has not been seriously
eroded, so the major shing industries continue to depend on
methods which in many respects have changed very little possibly
for centuries and certainly for decades.
One of the oldest organized sheries is that for herring—records
of an English herring shery go back to Saxon times. The principal
gear used in herring sheries is a gill net known as a drift net. This
net, made up of sections some 50 yards long and 10 yards deep, may
extend for three miles or so. The top corners of each section hang
from large oats while the rest of the net’s top, which is about six
feet below the surface, is buoyed up with a line of corks. A heavy
cable or warp holds down the bottom. Stretching like some giant
tennis net, it is towed gently along by the shing boat drifting with
the wind. During the night the herring move into the surface waters
to feast on the plankton there. When they meet the net barrier, they
try to swim through but the mesh is so gauged that only small fish