inter-array cables. Therefore, the magnitude of the impact from inter-array cable installation can be considered as low.
96.
In water depths greater than 20m Lowest Astronomical Tide (LAT), peak suspended sediment concentrations would be typically less than 100mg/l, except in the immediate vicinity of the area where jetting is occurring. However, in shallower waters of less than 5m LAT concentrations could potentially approach 400mg/l which is in excess of maximum naturally occurring concentrations recorded during metocean surveys (170mg/l).
97. On the basis of the information provided in chapter 7, Marine Geology, Oceanography and Physical Processes it is appropriate to consider the magnitude of the effect in terms of offshore and inshore sections of the export cable. The magnitude of the impact of increased SSCs and sediment re-deposition through ploughing, jetting, trenching, or mass flow excavation is classified as low for near field affects in the offshore areas of the export cable and negligible to medium for far field and near field effects respectively when considering shallower water.
11.6.1.2.1 Physiological Effects on Fish Species 98.
In general terms, juvenile and adult fish are mobile and would be able to avoid the localised areas disturbed by increased SSCs and sediment re-deposition. If displaced, they would be able to move to adjacent, undisturbed areas within their normal habitat range.
99.
Eggs and early larval stages of fish and shellfish do not however have the same capacity to avoid increased SSCs and areas affected by the re-deposition of sediment as adult and juvenile fish as they are either passively drifting in the water column or present on benthic substrates. The sensitivity of eggs and larvae is therefore considered to be higher than for later life stages and is the main focus of this assessment.
100. The re-deposition of sediments may affect fish eggs and larvae through smothering. Of the fish species, by virtue of being demersal spawners and the adhesive properties of the membranes, herring and sandeel eggs have the greatest potential to be affected by increased SSCs and sediment re-deposition.
101. Laboratory studies have established that herring eggs are tolerant to elevated SSCs as high as 300mg/l and can tolerate short term exposure at levels up to 500mg/l (Kiørboe et al. 1981). These studies concluded that herring eggs suffered no adverse effects from suspended sediment concentrations in excess of the maximum levels
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 11 Fish and Shellfish Page 49
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