Summaries of reviewed publications – references 1 – 5.

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 & Species

Fishing Technique




REF: 1



Shallow inlets and bays


(Fine to medium hard sandy sediments)

Beam Trawling

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


REF: 2


Shallow inlets and bays

(Coarse sand, gravel and broken shell)

Beam Trawling

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 natural disturbance.

Liverpool Bay

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.


REF: 3


Shallow inlets and bays

Scallop Dredging

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 species.

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.


REF: 4

Shallow inlets and bays


(Soft sediment)

Beam Trawling

Artica islandica 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.


REF: 5


Mudflats and sandflats

(Waders and wildfowl)

Mechanical cockle dredge

Experimental dredging using tractor towed cockle harvester.

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.


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