Fishery

Potential effects

Demersal fin fish, shrimp, Nephrops

Otter Trawling

· Trawl tracks visible for varying amount of time, depending on substrate, gear and tidal conditions ie. days or months.

· Top 10 - 60 mm of substrate disturbed.

·  Resuspension of sediment.

· Sediment structure may change from coarse grained sand/gravel to fine sand/coarse silt.

· Significant reduction in biomass of target and non-target species immediately after fishing operation. Likely to be more pronounced with extended recovery times, ie. many months, in areas with diverse communities and stable conditions.

·  Considerable variation in damage or mortality to affected species. Fragile, long lived, slow moving or sedentary species most vulnerable.

· Repeated trawling may cause benthic community structure to change, favouring more mobile species, rapid colonisers and juvenile stages.

· Influx of scavenging species post fishing operation.

· Biogenic reefs, eg. Sabellaria, and species that stabilise sediments, eg. eel grass, may be severely damaged resulting in resuspension of sediment.

Demersal fin fish

· ! Incidental catch of marine life including marine mammals and birds.

·  'Ghost fishing', dependent on condition of gear. In rocky less exposed areas may be active for months, on clean exposed ground, days to weeks.

Razor shell

· Subtidal dredge tracks, deeper than a conventional hydraulic cockle dredge (eg. 0.5 - 3.5 m wide, 0.25 - 0.6 m deep) visible for months in mobile sediments.

· Substantial physical disturbance of substrate

·  Significant reduction in abundance of non target species immediately after fishing operation. Weeks/months to recover to pre fishing levels in mobile sediment.

Scallops

·   Dredge tracks visible for varying amount of time ie. days or months in stable conditions a relatively minor fishery may have a significant cumulative effect on bottom micro topography.

· Top 60 -100 mm of substrate disturbed.

· Resuspension of sediment.

·  Significant reduction in biomass of target and non target species immediately after fishing operation. Likely to be more pronounced with extended recovery times, ie many months, in areas with diverse communities and stable conditions.

· Maerl crushed, smothered and killed.

·  Associated biota of maerl either caught, damaged or smothered by sediment.

Aquaculture

·   Impact on benthic communities through deposition of organic material (faeces and waste food).

· Development of anoxic conditions in sediment and water column in low energy site with subsequent outgassing of hydrogen sulphide and ammonia.

· Potential for hypernutrifiaction in low energy locations.

· Potential effects of sea lice treatments, antibiotics and antifoulants.

Aquaculture

· Manila clam cultivation in lays increases density of benthic species, changes in infauna and increased sedimentation.

·  Harvesting with hand raking reduces species diversity and abundance by 50 %, suction dredging reduces species abundance by 80-90%. Recovery to pre-harvesting levels may take long periods eg. 7 months.

· Trenching up to 10 cm deep, may take months to fill eg. 4 months in one study.

·  Accidental introduction of alien species.