Food in Abmzdmzce
39
accidentally come within their range. An alternative explanation is
that light has an indirect effect by luring the sh’s own food. In
American experimental sh—rearing programmes, copepods needed
to feed larvae of pelagic sh such as the mackerel and Pacic sardine
were gathered using a 1,000—watt underwater light connected to a
pump which was suspended several feet below the surface. But
whatever the explanation, the fact remains that lights do attract sh.
The U.S. Bureau of Commercial Fisheries have carried out experi—
ments with a combination of four submerged 1,000-watt lamps
and a 1,500—gallon—per—minute experimental pump in the eastern
Caribbean. Off Grenada the system delivered 234 pounds of
anchovies and sardines in an hour.
Undoubtedly pump shing and the like have a part to play in
sheries of the future, but existing techniques can still be sig—
nicantly improved, particularly by employing the reliable and
comparatively cheap man—made materials now available. Twines
made from substances such as polyamide, polyvinyl alcohol,
polyvinyl chloride, polyethy1ene and polypropylene are bringing
about a revolution in conventional gear. These new materials resist
rotting. In static tests carried out by the US
.
Naval Civil Engineering
Laboratory manilla rope left at depth in the sea for little over a year
was
severely damaged by micro-organisms and boring animals
whereas nylon and polypropylene ropes emerged practically un—
scathed from similar conditions. Man—made bres are strong,
elastic and do not soak up
water. As a result nets constructed from
them can be made larger and last longer. With the use of nylon
twines some seine nets have reached a length of over 600 metres.
Gill nets of transparent plastics have been shown to catch more sh
in clear waters than those made from conventional twine, and
terylene drift nets are now standard in most sheries. In Western
Australia crayshing activities are being extended through the winter
season
from April to August by shermen moving into waters
previously considered beyond the range of their ‘lobster pots’. Only
the strength of propylene rope used to lower the weighted pots
hundreds of feet down have made this possible. In fact new materials
together with a virtual doubling of power in modern shing vessels
like the distant water trawlers have brought the entire design and use
of shing gear under close scrutiny.
In the past, shing gear was improved largely on a trial and error
basis, but the development of at least one modern trawl has passed
39
accidentally come within their range. An alternative explanation is
that light has an indirect effect by luring the sh’s own food. In
American experimental sh—rearing programmes, copepods needed
to feed larvae of pelagic sh such as the mackerel and Pacic sardine
were gathered using a 1,000—watt underwater light connected to a
pump which was suspended several feet below the surface. But
whatever the explanation, the fact remains that lights do attract sh.
The U.S. Bureau of Commercial Fisheries have carried out experi—
ments with a combination of four submerged 1,000-watt lamps
and a 1,500—gallon—per—minute experimental pump in the eastern
Caribbean. Off Grenada the system delivered 234 pounds of
anchovies and sardines in an hour.
Undoubtedly pump shing and the like have a part to play in
sheries of the future, but existing techniques can still be sig—
nicantly improved, particularly by employing the reliable and
comparatively cheap man—made materials now available. Twines
made from substances such as polyamide, polyvinyl alcohol,
polyvinyl chloride, polyethy1ene and polypropylene are bringing
about a revolution in conventional gear. These new materials resist
rotting. In static tests carried out by the US
.
Naval Civil Engineering
Laboratory manilla rope left at depth in the sea for little over a year
was
severely damaged by micro-organisms and boring animals
whereas nylon and polypropylene ropes emerged practically un—
scathed from similar conditions. Man—made bres are strong,
elastic and do not soak up
water. As a result nets constructed from
them can be made larger and last longer. With the use of nylon
twines some seine nets have reached a length of over 600 metres.
Gill nets of transparent plastics have been shown to catch more sh
in clear waters than those made from conventional twine, and
terylene drift nets are now standard in most sheries. In Western
Australia crayshing activities are being extended through the winter
season
from April to August by shermen moving into waters
previously considered beyond the range of their ‘lobster pots’. Only
the strength of propylene rope used to lower the weighted pots
hundreds of feet down have made this possible. In fact new materials
together with a virtual doubling of power in modern shing vessels
like the distant water trawlers have brought the entire design and use
of shing gear under close scrutiny.
In the past, shing gear was improved largely on a trial and error
basis, but the development of at least one modern trawl has passed