Summaries of reviewed publications references 71 75.

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: 71

Shallow inlets and bays

Sandbanks

Bottom trawling

Effects of mobile fishing gear at three sites on a variety of bottom types in the Gulf of Maine were investigated.

Habitat complexity was reduced by direct removal of biogenic and sedimentary structures and the organisms that create structure eg. reduction of an extensive sponge community to the occasional small colony on large boulders, absence of previously widely distributed ascidian, reduced density of shrimp, dispersal of shell deposits by mobile gear. Authors discuss how this reduction in complexity may lead to increased predation on juveniles of harvested species and ultimately recruitment to harvestable stock especially in the northeast USA, where fish assemblages are part of a system where predation mortality on postlarval and juvenile fishes has a major effect on year-class strength.

Gulf of Maine

Auster et al., (1996) The impacts of mobile fishing gear on seafloor habitats in the Gulf of Maine (northwest Atlantic): implications for conservation of fish populations. Reviews in Fish.Sci. 4(2): 185-202.

REF: 72

Shallow inlets and bays

Sandbanks

Beam trawling

Analysis of bycatch of 7 fish and 10 invertebrate species taken in otter and beam trawls in an areas north west of the Netherlands which were registered annually between 1945 and 1983. A fisheries catchability model is developed using this data. For species with reliable field data the model results on long-term trends in abundance were in agreement with observations eg. considerable decrease in abundance of Roker and Common skate off Dutch coast between 1951 and 1960. Model also suggests that decline of landings of greater weever in early 1960s often considered to be due to severe winter and/or introduction of beam trawlers should also be attributed to effects of otter trawling. Most differences could be related to changes in gear and fishing effort with otter trawlers catching relatively more fish than invertebrates and beam trawlers catchability ten times higher than that of otters for all species considered.

Model estimates suggest that bottom fisheries had a considerable impact on the abundance of several bycatch species even before the Second World War.

Northwest Netherlands

Philippart, C. (1996) Long-term impact of bottom fisheries on several bycatch species of demersal fish and benthic invertebrates in the southeastern North Sea. ICES Annual Science Conference.

REF: 73

Shallow inlets and bays

Estuaries

Aquaculture

Two year study of macrofaunal succession and sedimentary biogeochemical parameters of seabed after intensive fish farming discontinued at 3 sites. All sites had low numbers of taxa at the beginning of the survey which increased in the two years but one site remained impoverished. The increase showed large fluctuations in one case which the authors attribute to a secondary input of organic material to the site which was considered to have set back recovery by at least 6 months. This points to the sensitivity of recovering sediments to additional stress. Improvements in terms of increased numbers of species and increased redox potential were recorded together with decreases in organic carbon, nitrogen and pore-water ammonia.

Loch Fyne & Loch Sunart

 

 

Nickell, T.D et al., (1998) The recovery of the seabed after the cessation of fish farming: benthos and biogeochemistry. CM 1998/V:1

REF: 74

Shallow inlets and bays

Sandbanks

Trawling

Study of the effects of extensive and repeated trawl disturbance over 18 months followed by 18 months recovery in an area which has been closed to fishing for over 25 years. Reference and treatment areas sampled.

Habitat effects. The relative differences in roughness between the treatment and reference areas increased during the disturbance programme and declined during the recovery period. The sediment in both areas was poorly sorted fine silt and trawling disturbance did not appear to have any effect on the sediment characteristics but trenches were left in the sediment by the trawl doors. Differences in organic carbon levels were not thought to be ecologically significant. More than 18 months was required before the physical characteristics of the sites became indistinguishable.

Species & community effects. Changes over time in abundance of individuals occurred at both sites but a treatment effect was also observed. Species numbers were greater at the treatment site after 16 months and remained so throughout the monitored recovery period. Numbers of some individuals were also significantly greater at the treatment site after 10 months disturbance (eg. Chaetozone setosa and Caulleriella zetlandica) only returning to similar numbers after 18 months recovery. Others declined in density (Scolopolos armiger and Nephtys cirrosa). There were no detectable effects on infaunal biomass. Community effects extended beyond the 18 month recovery period studied. Such recovery times suggest that even fishing during a restricted period of the year may be sufficient to maintain a community in an altered state.

Loch Gareloch

Tuck I.D., et al., (1998) Effects of physical trawling disturbance in a previously unfished sheltered Scottish sea loch . Mar.Ecol.Prog.Ser. 162:227-242.

[PR]

REF: 75

Shallow inlets and bays

Sandbanks

Water jet dredges

xperimental dredging in sandy areas swept by strong tidal flow with a paucity of epifauna but openings of numerous larger infaunal animals such as various bivalve species.Tests conducted using single fishing events rather than repeat fishing.

Habitat effects. Trenches up to 2m wide and 0.15 deep at centre were observed. These started to fill after 5 days and were no-longer visible after 11 weeks but sediment in the tracks remained fluidised under a thin crust of firm sediment. Long term physical effects are less well understood and may be exacerbated by repeated fishing of the same area.

Species and community effects. Immediate reduction in number of species, individuals and biomass in fished tracks but measures of diversity showed no effects. Abundance of polychaetes reduce and of amphipods increase. Crab species moved into the region to scavenge of material disturbed by the dredge. The results suggest biological effects are only short term. No effects were recorded after 11 weeks. Species likely to be damaged (eg.heart urchins and large bivalves) were rare in the samples but present in dredge catches where damage was noted.

Most of the animals in the sediments are adapted to a mobile environment so other than being removed or displaced they were not thought to be greatly affected by the dredging. On the basis of this work difficult to comment on areas with more obvious and diverse epifauna. Authors conclude there is little difference between the biological impact of water jet dredges and suction dredging although the latter may have a greater physical effect and fish less selectively.

Western Isles

Fisheries Research Services (1998) A Study of the effects of water jet dredging for razor clams and a stock survey of the target species in some Western Isles populations. Marine Laboratory, Aberdeen Report No. 8/98.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Next section