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
Sandflats and mudflats
Laboratory experiments to see whether non-lethal
burial or exposure on the sediment surface
could alter the normal living depth of Mya
arenaria in sand and mud.
Species and community effects - After
2 weeks those buried under 1-15cm of medium
fine sand were buried deeper than controls
whereas clams exposed on the sand surface
(and had subsequently reburrowed) were able
to re-establish their normal living depths.
Clams under 1-15cm of mud attained their normal
living depth within two weeks but exposed
clams reburrowed to abnormally shallow depths.
The increased likelihood of predation at shallow
sediment depths was compounded by the 60%
lower reburrowing speed of exposed clams in
mud when compared to sand.
Conclusions were that negative impacts of
clam digging on M. arenaria are not
limited to removal of market-size clams and
shell breakage of remaining ones. Exposure
of prerecruits and depositions of tailings
on clams adjacent to harvest sites may increase
susceptibility of unharvested clams to predation,
dessication or freezing. The effects depend
on different substrate types. Mortality will
be greater on clam flats having a mud substrate
than of medium-fine sand. Management practice
should reflect these differences. On sandflats
there would be little to be gained from breaking
up the clumps of soil turned over since tailing
burial will probably not result in mortality.
In muddy areas, reducing tailing piles is
likely to enhance survival of both buried
and exposed clams.
Emerson C.W., Grant J. & Rowell T.W.
(1990). Indirect effects of clam digging on
the viability of soft-shelled clams Mya
arenaria. Netherlands Journal of Sea Research
Shallow inlets and bays
Field experiment of impact of fishing for
razor clams Ensis sp. by hydraulic
dredging on the associated infaunal community,
Species and community effects - Infaunal
samples were examined at 1 and 40 days from
fished and unfished plots. There were differences
in mean number of species and individuals
for control and fished sites 1 and 40 days
later but only total numbers of individuals
significantly lower. After 40 days no detectable
difference. No statistically significant differences
in the 10 most abundant species Bathyporeia
elegans, Siphonoecetes kroyeranus, Exogene
hebes, Spio filicornis, Corophium crassicorne,
Streptosyllis websteri, Cochlodesma praetenue,
Nephtys cirrosa, Megalorupus agilis and
Perioculodes longimanus between treatments
after either 1 or 40 days.
Suction dredging for Esnis had profound
immediate effects on benthic community structure
with consistent reductions in the numbers
of many macrofaunal species and the target
species. However, despite the relatively large
scale nature of the disturbance, these effects
appear to persist for only a short period.
After 40 days no detectable difference - visually
or from macrobenthic community analysis, effects
on long-lived bivalves could however be more
serious, and action of the dredge is violent
enough to often crack shells of adult Arctica
islandica. Larger polychaetes and crustaceans
are also often retained on the conveyer, crushed
in the mechanism or fall off the end to fall
at random on the seabed. No estimate was made
of survivorship of these individuals but many
scavenging hermit crabs were active immediately
after dredging. Migration and passive translocation
play a part in returning the abundance of
species to pre-impact levels. Authors suggest
that local population reductions due to dredging
are only likely to persist in a habitat if
one of two conditions are met: (a) macrobenthic
populations themselves, or the sediments in
which they live, are immobile or (b) the affected
area is large relative to the remainder of
the habitat such that dilution effect cannot
occur. For most habitats where Ensis
could be fished authors believe that neither
of these conditions likely to hold. Current
technology restricts this type of fishing
to approximately 7m therefore likely to be
strongly influenced by wind and tide-induced
currents in these areas. Sediments are probably
mobile and effects will be diluted rapidly.
However they note there is little knowledge
of the relative importance of the various
processes which contribute to animal movement
and whether certain habitats may be more susceptible
to persistent damage than others. At most
sites the authors believe there will be adequate
areas to dilute effects but prior examination
of potential fishery sites is warranted.
Loch Gairloch, Scotland
Hall S.J., Basford D.J. & Roberts M.R.
(1990). The impact of hydraulic dredging for
razor clams Ensis sp. on an infaunal
community. Netherlands Journal of Sea Research
Target species removed in great numbers,
long-lived bivalve species often damaged or
killed and smaller-bodied infauna either displaced
or killed. With the exception of large bivalves,
it would appear that effects on macrofaunal
community in general are not locally persistent,
although in calmer seasons effects may persist
for longer than observed here. Another consideration
is that if Ensis and other large bivalves
play an important role in structure of benthic
communities, their removal would result in
cascading effects over long time scales. But
in the high levels of sediment mobility at
the study site, this hypothesis was considered
Shallow inlets and bays
Beam and Otter trawls
Long term historical record (1945-1981) of
by-catch from an area of the North Sea to
the Northwest of the Netherlands at Zoological
Station in Den Helder.
Species and community effects - Bottom
fisheries have a considerable effect on many
by-catch species including demersal fish and
invertebrates. Numbers of by-caught fish and
invertebrates related to changes in fish gear
and effort of bottom trawlers. Catchability
of beam trawlers 10x higher than otter trawls.
Model of bottom fisheries shows that bottom
trawling has reduced the abundance of several
demersal fish and invertebrates to very low
levels within 35 years.
Philippart C.J.M. (1996). Long-term impact
of bottom fisheries on several bycatch species
of demersal fish and benthic invertebrates
in the southeastern North Sea. ICES C.M. 1996/Mini
Fixed salmon nets
Investigations by the author into numbers
of dead seabirds on the shore in early 1970s
at Cruden Bay in NE Scotland in mid summer
led to a conclusion that they must have been
killed in some of the numerous local fixed
salmon nets which were often seen holding
dead birds. Most were auks which are known
to be killed in fixed salmon nets on a considerable
scale around the seabirds colonies on St.
Abbs Head and Troup Head in the Moray Firth.
Some shags also reported killed in nets set
near a roost on the Summer Islands. Off the
Scottish Wildlife Trust reserves at Longhaven
and on the Dunbuy Rock to the south up to
17 bodies per net were recorded on the 12
or so occasions they were examined during
the breeding season over the previous four
Cruden Bay, NE Scotland
Bourne W.R.P. (1989). New evidence for bird
losses in fishing nets, Marine Pollution Bulletin.
Shallow inlets and bays
Trials looking at effects of three types
of trawling gear on bottom sediments. Shallow
traces made by inshore and offshore scallop
dredging could be distinguished from each
Habitat effects - Scallop dredging
observed to lift fine sediments into suspension,
bury gravel below the sand surface, and overturn
large rocks embedded in the sediment, appreciably
roughening the bottom. The inshore Alberton
dredge was inefficient, dumping its contents
back on to the bottom at intervals.
Trawl tracks were seen as grooves on the
seafloor - considered to be made by otter
trawl doors. Suspended sediment in dredge
tracks reduced visibility from 4-8m to less
than 2m within 20-30m of the track but dispersed
within 10-15mins, coating the gravel in the
vicinity of the track with a thin layer of
fine silt and obscuring Lithothamnion.
Offshore dredge - gravel fragments overturned.
Depressions left by tow bar of the dredge.
Gravel less frequent inside the track. Inshore
dredge (Alberton) tracks left, gravel sparser
inside and dislodged boulders commonly observed.
Tooth marks over sandy bottom.
Bottom type and hydrographic regime in the
Bay probably allowed marks made by fishing
gear to remain recognisable for a long time
as tidal currents faster than 1km/hr were
not encountered. Even a relatively minor fishery
may therefore have a significant cumulative
effect on bottom microtopography under these
conditions. Scallop and otter tracks could
be distinguished, scalloping contributing
to an appreciable roughening of the bottom,
lifting large boulders and overturning many
of them, presumably leading to destruction
of the epifauna on their upper surfaces. Under
strong tidal flow author considers that intensive
dredging will lead to erosion of sediment
lifted into suspension by the dredge - this
aspect needs more study.
Species and community effects - Dredging
caused appreciable lethal and sublethal damage
to scallops left in the track. Damage greatest
on rough bottom. Predatory fish and crabs
were attracted to dredge tracks within 1hr,
and fish were observed in the tracks at densities
3-30 times those observed outside the tracks.
There was a pronounced and rapid aggregation
of foraging fish - a natural response which
also occurs in the absence of fishing operations.
Chaleur Bay, Gulf of St Lawrence
Caddy J.F. (1973). Underwater observations
on tracks of dredges and trawls and some effects
of dredging on a scallop ground. Journal of
the Fisheries Research Board of Canada 30: