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 Many different types of fishing gears are used in Italian waters and these can be classified into two main groups. Active gears include bottom and pelagic trawls and seines which move through
the water and herd or surround the fish. Passive gears include hooks, fixed nets
and traps which rely on attraction or the natural movement of fish to make contact
between fish and gear. Most of commercial species landed
in Italy are caught by
towed gears (mainly by towed nets). The towed nets are complex combinations/assemblages
of netting, wires, spreading devices, weights and floats. Understanding how they
perform in the hostile environment in the sea is important if the efficiency of
the operation is to be optimised. To this goal the Fishing Technology Unit (FTU) initiated the use of instrumentation to measure the engineering performance of fishing
gear in the 1968. Since then, a comprehensive set of instrumentation has been developed
to measure the gear performance, the netting material properties and the associated
environmental parameters which influence gear efficiency. The performance of towed
nets are monitored using different instrumentation. Acoustic sensors provide information
about gear geometry: door spread, horizontal net opening (defined as upper net wing-end
spread) and vertical net opening (defined as height of the headline centre above
the seabed). Moreover, two electronic load cells are used to measure the warp loads
and two underwater force sensors are inserted just in front of the wing-ends to
measure the net drag ahead of the wing tips. All the instruments are linked to a
personal computer, which automatically controls the data acquisition and provides
the correct functioning of the system in real time. All this make us able to control
the underwater conditions and other critical data, and to improve catches using
less time and less fuel. Graphical data presentation makes it easy to detect errors
and to act fast when needed.
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