 | FAO/FIIT Fishing Gear Type Fact-Sheet |
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| Midwater otter trawls [OTM] | updated : 10-mai-2001 |
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| Profile |
| General Description: A midwater otter trawl is a cone-shaped
net which is towed in mid-water. It consists of a
cone-shaped body, normally made of four panels, ending in a
codend and the net has lateral wings extending forward from
the opening. The horizontal opening is maintained
byotter boards. Floats
and/orsailkites on the headline
and weights on the groundline provide for the vertical
opening. Large modern midwater trawls are rigged in
such a way that the weights in front of and along
thegroundline provide for the
vertical opening of the trawl. The cable transmitting
acoustic signal form the net sonde might also provide a
lifting force that maximize the vertical trawl opening. To
reduce the resistance of the gear and achieve a large
opening, the front part of the trawls are usually made from
very large rhombic or hexagonal meshes. The use of nearly
parallel ropes instead of meshes in the front part is also a
common design. The largest mesh sizes used so far are 128 m
and, on modern large midwater trawls, approximately three
quarters of the length of the trawl is made with mesh sizes
above 400 mm. |
| Specific Equipment: Hydrodynamic designed otter boards are
used for midwater trawling. The fishing depth is usually
controlled by means of anet
sounder (netsonde) or depth recorders. As for
other types of trawls,catch
sensors can be installed in
thecodend to give information
about the amount of caught fish.Tension
sensors can also be used in combination with
balanced winches to guarantee a stable, optimal opening.
Horizontalsonars and fish
finding equipment is a prerequisite for successful operations. |
| Specific Handling Equipment: Most of the vessels engaged in
midwater trawling are equipped withnet
drums.Trawl
winches installed on deck control
thewarps and store them when not
in use. The larger midwater trawlers use pumps for emptying
the codend. |
| Fishing Vessels using this gear: Midwater otter trawls are used especially
by stern trawlers. |
| Fishing Operations: A midwater otter trawl is towed by a single
boat. Midwater trawling is a well-aimed fishing activity.
The fish shoals are located by sonar (but some midwater
trawling can also be carried out on slightly scattered fish
staying in a given layer of water) and the vessel is towing
in the direction of the shoal. The fishing depth level,
which is controlled by the net sounder, is regulated by the
length of the warps and/or the towing speed. |
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| Features |
| Target Species: Pelagic species, mainly fish
andcephalopods,northern
shrimp (also small crustaceans, krill) |
| The Gear and its Environment:
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 | Deployment Area: Midwater, or pelagic, fishing is
carried out mainly at sea, on the continental shelf,
sometimes in deeper waters, also in some lakes. |
| Impact on the Environment: No impact on bottom habitat and
bottom structure. |
| Impact on Aquatic Species: In most cases it is a single
species fishery, bycatch rates of other species are
low. Incidental catch ofdolphins and marine mammals may
occur in some areas, |
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