 | FAO/FIIT Fishing Gear Type Fact-Sheet |
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| Bottom trawls [TB] | updated : 10-mai-2001 |
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| Profile |
| General Description: A bottom trawl is constructed like a
cone-shaped net that is towed (by one or two boats) on the
bottom. It consists of a body ending in a codend, which
retains the catch. Normally the net has two lateral wings
extending forward from the opening. The mouth of the trawl
is framed byheadline
andgroundrope. It is designed and
rigged to catch species living on or near the bottom. Bottom
contact with the gear is needed for successful operations.
Three categories of bottom trawls can be distinguished based
on how their horizontal opening is maintained: beam
trawls, bottom otter trawls,
and bottom pair
trawls. Beam trawls are commonly designed
without wings. |
| Specific Equipment: The groundrope equipped
withrubber
discs,bobbins,
spacers etc. protect the trawl from damage. On very rough
bottom special rock hopper gears are used. Beam trawls are
designed and equipped in a different way. |
| Specific Handling Equipment:
Trawl winches installed on deck
control the trawling warps and store them when not in
use.Gilson winches and
lifting tackles support the handling on deck. |
| Fishing Vessels using this gear:
Bottom Trawlers range in size
from small, undecked boats, powered by outboard engines up
to large vessels with up to 8000 HP engines and size up to
3000 GT. |
| Fishing Operations: Bottom trawls are designed and rigged to
have bottom contact during fishing. They are towed across
the bottom at speeds ranging from 1 to 7 knots (0.5-3,5
m/s), frequently between 3 and 5 knots. Duration of a tow
mainly depends on the expected density of fish (whether fish
is aggregated or not)the shape of the bottom and the slope
in the fishing area, from a few (10-15 minutes) up to 10-12
hours, commonly 3-5 hours. |
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| Features |
| Target Species: Bottom and demersal species |
| The Gear and its Environment:
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 | Deployment Area: Bottom trawls can be operated in a
very wide range of depths (from a few meters to
1500-2000 m), mainly at sea, but also, in some cases in
inland waters e.g. lakes. |
| Impact on the Environment: Bottom trawls interact physically
with the bottom sediment, which might result in
removal or damage of sedentary living organisms
(including seaweed and corals) and in the case of
uneven bottom surface displacement of stones or
other larger objects. On flat sandy/muddy bottom the
sediments might be whirled up into the water masses
and suspended. The short and long-term impact on the
bottom environment is poorly documented despite some
scientific experiments. More research on possible
impact of bottom trawling is urgently needed to
evaluate the effect on the environment. |
| Impact on Aquatic Species: The major potential detrimental
impact of bottom trawling on species can be the
capture and removal from the ecosystem of small
sized organisms and non-target species, which
frequently are discarded at sea. Such impact can be
mitigated by using larger meshes in the codends
and/ordevices in the
trawl that reduce capture of small and unwanted organisms. |
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