 | FAO/FIIT Fishing Gear Type Fact-Sheet |
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| Bottom pair trawls [PTB] | updated : 10-mai-2001 |
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| Profile |
| General Description: A bottom pair trawl consists of a
cone-shaped body, normally made of two or four (and
sometimes more) panels, closed by a codend and with lateral
wings extending forward from the opening. |
| Specific Equipment: Long heavy cables
(bridles) of steel or combination
rope may be inserted between the net and the warp to
increase the catching width of the trawl gear. 4-500 meters
of such cables will result in a fishing width of 4-500
meters, which is more than twice the width of a
conventionally rigged single otter trawl. This rigging
require smooth bottom, while a rigging with shorter bridles
with a heavy weight attached at the joining to the towing
warp is more commonly used on rougher grounds. |
| Specific Handling Equipment: Only one drum of the trawl winch is
required on each of the two trawlers to handle the warp of
each side. |
| Fishing Vessels using this gear: A pair trawler may be an open boat with an
outboard engine, or any vessel up to 60 meters trawlers. The
pair trawlers are normally of similar power and sizes. This
fishing practice is often used by non powered vessels (small
to medium size engines). |
| Fishing Operations: Thebottom pair
trawling is operated by two vessels, each
towing a trawl warp attached to the bridles in front of the
two trawl wings. One of the vessels is handling the trawl
and takes the catch. The other is only a towing vessel, the
so-called "slave". It is a common practice to
alternate the operation between the two vessels. Equal
towing pull by the two vessels are very important to
ascertain that the trawl is symmetric during fishing. This
can be controlled by usingtension
meters or recently
developedsymmetry sensors.
Another important operational parameter is to maintain
correct and steady distance between the two towing vessels.
Radar measurements is commonly used for this purpose and for
smaller boats a connecting line between the vessels will do
the job. |
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| Features |
| Target Species: Bottom fish,
includingflatfish and to a lesser
extent shrimp. |
| The Gear and its Environment:
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 | Deployment Area: Bottom pair trawls can be operated in
very shallow waters (2-5 meters) to depths down to 5-800
meters, in marine and inland waters. |
| Impact on the Environment: Similar to single bottom otter
trawl, except thatpair
trawls do not have the ploughing impact
of trawl doors. |
| Impact on Aquatic Species: The major negative impact of bottom
pair trawls on the biological environment is related
to the capture and frequently discarding of non
target sizes and species both of fish and non-fish
species. Regulation concerning minimum mesh size in
the codend is the most commonly used methods to
limit the capture of non-target fish sizes. In
recent years such size selectivity has been improved
by the introduction of square mesh codends and
selection devices like grids. |
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