Summaries of reviewed publications references 21 25.

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

Effects

Locations

Reference

REF: 21

Shallow marine inlets

Estuaries

(Muddy gravel)

Clam dredge

Treatment and control type dredging experiment, 2 passes of a modified oyster dredge.

Habitat effects - Sediment removed to a depth of between 15-20cm by dredging and gravel fraction reduced. Sediments may become more anoxic after dredging. Dredge tracks most likely to be filled with fine sediment in low energy conditions therefore discrete habitat variation will be created. Resuspended sediment may have serious survival implications for species unable to deal with heavy suspended sediment loads.

Species and community effects - Due to the deep penetration of the dredge all fauna, with the exception of bivalves (eg Abra tenuis, Cerastoderma edule and Mya arenaria) were removed completely in the short term. It is likely that these organisms were dislodged and then redeposited by the dredge or that they migrated or were passively dispersed into the area from adjacent undredged areas. Annelids were most badly affected by the dredge with the exception of Tubificoides benedeni and a Phyllodocid. Abundance of bivalves was also greatly reduced but some found in some dredged samples (small specimens thought to have been disturbed by the dredge and re-deposited afterwards).

No clear recovery of fauna evident over the 8 day period of study but opportunistic polychaetes (eg Capitella capitata and Tubificoides benedeni) likely to be early colonisers of disturbed mudflats along with the surviving bivalves. Authors suggest these will be followed by active polychaete species eg Eteone longa and more stable habitat species such as Cirriformia tentaculata. Continual disturbance will not favour stable habitat species, high biomass communities may occur but are unlikely to contain individuals of high biomass which may be exploited as a food source by birds.

Langstone Harbour

Southern Science (1992). An experimental study on the impact of clam dredging on soft sediment macro invertebrates. Report to English Nature.

REF: 22

Shallow bays and inlets

Sandbanks

Trawling

Laboratory based experiment investigating the behaviour of Buccinium undatum exposed to different prey items.

Species and Community effects - Less mobile scavengers such as whelks may take several days to arrive at sites of trawl disturbance. Whelks are well suited to exploit fisheries discards as they are very responsive to chemosensory stimuli exuded from damaged or moribund animals. 98% of whelks caught in a beam trawl survive. Whelks are capable of exploiting a wide variety of prey due to their flexible feeding behaviour. In this experiment they ate Liocarcinus depurator, Spatangus purpureus, Trisopterus minutus but not Pleuronectes platessa. Where whelks are common they have an important capacity in utilising energy from dead or damaged animals. Whelks using this competitive advantage may exhibit local population increases and in areas of intense beam trawling, such as the southern North Sea, dead or moribund animals which result from these activities could make up a considerable proportion of the whelk diet.

 

Evans P.L. Kaiser M.J. and Hughes R.N. (1996). Behaviour and energetics of whelks, Buccinium undatum (L.), feeding on animals killed by beam trawling. Journal of Experimental Marine Biology and Ecology. 197: 51-62.

[PR]

REF: 23

Harbour porpoise

 

Record of causes of death in 422 cetaceans of 12 species stranded on the coasts of England and Wales between August 1990 and September 1995 via post-mortem examination.

Most frequent cause of death in harbour porpoises and common dolphins was entanglement in fishing gear. 38% of harbour porpoises and 80% of common dolphins diagnosed as being by-caught. The proportion of by-caught harbour porpoises increased from 1990 to 1995. Factors such as changes in fishing effort, technique or location or changes in the abundance or distribution of harbour may account for this. Probably an underestimate of the true incidence of by-catch in cetaceans. Estimates of the number of by-caught harbour porpoises cited as being between 328 and 552 by English fishing fleets on the Celtic shelf. The proportion of starved neonatal harbour porpoises higher than starved common dolphins may relate to the more coastal distribution of harbour porpoises. More coastal distribution of harbour porpoises may also increase their contact with co-factors such as pollutants making them more likely to die from species-specific pathogens than common dolphins. By-catch is a threat to both harbour porpoises and common dolphins around the coast of England and Wales. Of 7 Tursiops truncatus studied only one was determined as being by-caught.

 

Kirkwood J.K., Bennett P.M., Jepson P.D., Kuiken T., Simpson V.R. & Baker J.R. (1996). Entanglement and other causes of death in cetaceans stranded on the coasts of England and Wales.

REF: 24

Sand banks

Shallow inlets and bays

Beam trawling

Side scan sonar investigation into the effects of beam trawling in the southern part of the Danish North Sea.

Habitat effects - Poorly preserved trawl marks were widely distributed in the study area except in one area of presumably coarse grained sediments where there were numerous extremely well-preserved beam trawl marks. The substrate appears to have altered from coarse grained sand or gravel to fine sand and coarse silt in the trawl marks as shallow scouring and smoothing from beam trawling created conditions favouring fine sand/coarse silt sediment filling the tracks. Effects of beam trawling on sediment may be long-term and in some areas may have resulted in a definitive change of the substrate with implications for the benthic community.

Southern North Sea

Leth J.O. & Kuijpers A. (1996). Effects on the seabed sediment from beam trawling in the North Sea. ICES 1996. Annual Science Conference. Mini-symposium: "Ecosystem Effects of Fisheries". ICES C.M. 1996/Mini 3.

REF: 25

Sand banks

Shallow inlets and bays

Beam trawling

Experimental investigation into changes in sediment structure, in- and epifauna, mortality of by-catch and effects on predators caused by beam trawling with the application of twice-yearly fishing perturbations.

Species and community effects - Trawling causes changes in the abundance of some in- and epifaunal species. Infaunal diversity reduced by 54%, epifaunal diversity not significantly altered. Mortality of animals retained in the cod-end studied by placing them in tanks. Results varied greatly between taxa. Mortality greatest for fish and animals with brittle skeletal structure such as sea urchins and swimming crabs, and very low for starfish, brittlestars and hermit crabs. Benthic species which are most likely to benefit from the increased scavenging opportunities brought about by trawling were starfish and hermit crabs.

Red Wharf Bay and Dulas Bay in Liverpool Bay

Kaiser M.J., Ramsay K & Spencer B.E. (1996). Short-term ecological effects of beam trawl disturbance in the Irish Sea. A review. ICES C.M. 1996/Mini 5.

 

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