Details are limited to information relevant to
the UK marine habitats and species listed in the
Habitats Directive and the Birds Directive.
[pr] indicates that the paper is from a peer reviewed
journal or report
Natura 2000 Habitats &
Shallow inlets and bays
(Fine to medium hard sandy sediments)
Pre and post experimental investigation,
within 30m depth contour, with 7 tonne, 12m
beam trawl including 5x22mm and 3x18mm tickler
chains, 3x20mm and 8x14mm net tickler chains,
mesh size of 9cm in the cod-end. Area trawled
three times over 2 days and samples taken
up to 2 weeks after trawling.
Habitat effects - Tickler chains penetrate
at least 6cm into the sediment surface indicated
by catches of Echinocardium cordatum
and Arctica islandica. Tracks made
by the beam trawl shoes still apparent on
sidescan sonar after 16hrs.
Species and community effects - Some
benthic species show a 10-65% reduction in
density after trawling the area three times.
There was a significant lowering of densities
(40-60%) of echinoderms Asterias rubens
and small E. cordatum, and of polychaete
worms Lanice conchilega and Spiophanes
bombyx. Vertical distribution in sediment
appears to be an important factor in catchability.
Decrease in density (10-20%), although not
significant for small crustaceans and larger
Tellina fabula and E. cordatum.
Except for the starfish A. rubens most
of these animals live in the sediment at a
depth up to 15cm. The effect of beam trawling
on densities of small individuals tends to
be much greater than on densities of large
individuals (larger animals tend to live deeper
or have better escape possibilities). The
polychaete worm Magelona papillicornis
showed a considerable increase in numbers,
this may be attributable to a change in the
vertical distribution of the species in the
sediment. The numbers of small Ophiura
living in the top centimetre of sediment did
not change after trawling the area three times,
suggesting the species escape unharmed through
the net mesh. Also no direct effect on densities
of molluscs (except T. fabula) and
worms (except Magelona papillicornis,
L. conchilege and S. bombyx).
Less abundant worm species (including Spio
filicornis Scolelepsis bonnieri, Scoloplos
armiger and Owenia fusiformis)
and less abundant molluscs (including Thracia
sp. Venus striatula, Montecuta ferruginosa
and Mysella bidentata) showed no change
in total density after trawling. About 90%
of A. islandica caught by the 22m trawl
were severely damaged.
Conclusions were that direct effects on some
benthic species in the area appears to be
considerable and that beam trawling may contribute
to changes in benthic systems in the North
Sea. However, direct effects cannot be extrapolated
to interpret long-term effects as there was
no comparison with untrawled areas.
Southern North Sea
Bergman M.J.N. & Hup M. (1992) Direct
effects of beam trawling on macro-fauna in
a sandy sediment in the southern North Sea
ICES Journal of Marine Science. 49:5-11
Shallow inlets and bays
(Coarse sand, gravel and broken shell)
Experimental beam trawl over a 4x2km area,
at a depth between 26 and 34m. commercial
beam trawl, weighing 3.5 tonne fitted with
a chain matrix and 8cm diamond mesh cod-end
used. Waylines were fished either 10 or 20
times to adequately disturb trawl area.
Habitat effects - Physical characteristics
of the surface sediment were altered by the
passage of the beam trawl but effects varied
in different parts of the experimental area.
Surface roughness of the relatively uniform,
stable, flat areas were not altered by trawling
but lowered in fished sites in the SE sector
which was characterised by sand waves and
some ripples. In the latter case the surface
ripples were flattened but the megaripples
were unaffected. Passage of the chain matrix
may have caused sediment to become unconsolidated
as shell and gravel currents. Conclusions
were that particle size distribution was not
affected and observed changes may only be
in the superficial layers of the sediments.
Newly exposed shell and gravel material would
provide surfaces for recolonisation and settlement,
epizoites on surfaces which were overturned
would be smothered.
Species and community effects - Beam
trawling altered the benthic community structure
in the uniform, stable, flat areas having
a measurable deleterious effect on the number,
abundance and diversity of taxa. Of the top
20 most common taxa, abundance of 19 were
lowered at fished sites, 9 of which were statistically
significant. Fragile infaunal species which
live on or within the surface sediments (bivalves,
holothurians, gastropods) were particularly
vulnerable to damage or disturbance. The abundance
of sedentary and slow-moving animals organisms
was significantly lowered. Some animals were
fatally injured or crushed, others only damaged
(eg cropping of Mya siphons). Tissues
of animals damaged by beam trawling rapidly
attract scavengers. Analysis of diet indicated
they were feeding on the damaged animals,
most notably Ampelisca spp. There were
no detectable differences in the diversity
and abundance of taxa in the areas characterised
by mobile sediments and subject to frequent
Kaiser M.J. & Spenser B.E. (1996) The
effects of beam trawl disturbance on infaunal
communities in different habitats. Journal
of Animal Ecology. 65:348-358.
Shallow inlets and bays
Large scale investigations on soft sediment
communities depth between 12-15m, 2km offshore.
Six vessels towing 3m wide commercial 'Peninsula’
dredge with scraper/cutter bars not extending
below the dredge skids. Site dredged for 3hrs
day-1 over 3 days covering the
dredge area at least twice. Dredging intensity
typical of local commercial fishing intensity.
Habitat effects - Typically top 2cm
of surface sediment disturbed but up to 6cm.
Observations 8 days after dredging revealed
seabed formations such as pits and depressions
filled in and mounds formed by burrowing shrimps
removed. Parallel tracks from dredge skids
apparent after dredging. Physical changes
in the seabed still apparent one month post-dredging.
Six months post dredging most physical features
reformed (abundance and size of callianassid
mounds similar to those present before dredging)
however some flattened areas still apparent.
No physical differences between dredged and
control sites after 11 months.
Species and community effects - Number
of species in dredged areas decreased significantly.
Maximum impact did not occur immediately after
dredging suggesting some indirect ecological
changes such as uncovered organisms becoming
more vulnerable to predation by invertebrates
and demersal fish. Most species decreased
in abundance by approximately 20-30% in the
3.5 months after dredging. The duration of
the decrease in abundance species varied with
effects still apparent in some species after
8 months and in two species up to 14 months
although this was possibly due to undersampling
in the pre-impact period. 11 animals not found
in the sample area after dredging, mostly
sedentary and therefore unable to re-establish
except by larval recruitment.
Susceptibility to dredging not correlated
to feeding type or rarity. Fragile groups
such as nemerteans were greatly damaged by
dredging, polychaetes probably cut and killed
by passing dredge. Other species may have
been affected by high rates of dredging induced
sedimentation, which may be 2-3 orders of
magnitude greater than storm produced sedimentation,
or buried when depressions filled in. Two
species showed significant increase in abundance
following dredging (Diamorphostylis cottoni
and Oedicerotid sp.) whereas the
isopod Natalolona carppulenta decreased
sharply and then increased to be consistently
higher on the dredged plot for 8 months possibly
due to greater availability of prey.
Seasonal and interannual changes in community
structure much greater than those caused by
dredging. Long-lived and slow recruiting epifaunal
species (eg sponges and ascidians) likely
to be particularly vulnerable to dredging.
Long-term effects may be different to the
short and medium-term effects. Needs to be
studied over longevity of longest lived component
Port Phillip Bay, Australia
Currie D.R. & Parry G.D. (1996). Effects
of scallop dredging on a soft sediment community:
a large scale experimental study. Marine Ecology
Progress Series. 134: 131-150.
Shallow inlets and bays
used as an indicator species for investigation
of long-term effects of beam trawling intensity
in the North Sea.
Species and community effects - A
high incidence of damage found on shells of
Artica islandica from highly fished
areas particularly in the south eastern North
Sea. In specimens with two values only 10%
of the SE North Sea specimens were undamaged
and in other areas around 40% undamaged. 80-90%
of the damage found on posterior ventral side
of the shell explained by the orientation
of the living shell in the upper sediment
layer and the horizontal motion of tickler
chains. Observed trends in the occurrence
of shell scars per year show a striking coincidence
with the increased capacity of the Dutch beam
trawling fleet since 1972. Another effect
may be on age frequency distribution as juveniles
(1-4cms) were rarely found in the SE North
Sea. Less resistance to damage may be a factor
although the authors indicate that other researchers
have contradictory information on this.
North Sea with sampling clusters in the NW,
mid-west and SE
Witbaard R. & Klein R. (1994). Long-term
trends on the effects of the southern North
Sea beamtrawl fishery on the bivalve mollusc
Artica islandica L. (mollusca, bivalva).
ICES Journal of Marine Science. 51: 99-105.
Mudflats and sandflats
(Waders and wildfowl)
Mechanical cockle dredge
Experimental dredging using tractor towed
Habitat effects - Vehicle tracks and
dredging furrows created.
Species and community effects - Dredging
attracted black-headed and common gulls which
fed on very small prey items lying on the
surface of harvested furrows including Crangon,
Corophium, broken cockles, intact small
cockles which pass through the drum, and polychaetes.
The number of birds attracted and the places
they fed depended on the abundance of prey
items revealed by harvesting and presence
of people. Peak count at Llanrhidian was 200
black-headed gulls and 55 common gulls, mostly
adults which fed preferentially in the most
recently harvested furrows. Other species
present were curlew, dunlin and oyster catchers.
The increased feeding activity of birds was
short lived, 14 days for oystercatchers and
7 days for gulls and small waders. Significant
reduction in bird feeding activity apparent
thereafter and still detectable after four
months. Oystercatchers responded more quickly
to changes suggesting harvesting may have
been less disruptive or recovery quicker.
Overall the short term increase in the number
of gulls and waders in the harvesting area
was followed by a long term significant reduction
in feeding opportunities for bird species.
Birds may then leave to find food elsewhere,
leading to the considerable alteration in
normal seasonal distribution pattern of shorebird
populations. Average density of birds were
reduced in this trial by between 15 and 75%
in harvested area.
Burry inlet (east of Whiteford Point and
northern edge of Llanrhidian marsh)
Ferns P.N. (1995). The effects of mechanised
cockle harvesting on bird feeding in the Burry
Inlet. p11-18. In Burry Inlet & Loughor
Estuary Symposium, March 1995. Part 1. Burry
Inlet and Loughor Estuary Liaison Group.