waters of depths below 5m is considered to be medium in the near field where jetting is used for cable burial. However, as crabs and lobsters migrate offshore to spawn in deeper waters (Edwards 1979) and the area of habitat affected by the inshore section of the offshore export cable corridor is proportionally small, the magnitude in relation to this receptor low.
107. The impact of an increase in suspended sediment concentrations on general fish and shellfish egg and larval development is therefore assessed to be of minor adverse significance.
11.6.1.2.3 Physiological Effects on Sandeels 108. As sandeels spend a major proportion of their life cycle buried within the sea bed, increased SSCs and sediment re-desposition have the potential to adversely impact this species group.
109. Sandeels deposit eggs on the sea bed in the vicinity of their burrows between December and January. Grains of sand may become attached to the adhesive egg membranes. Tidal currents can cover sandeel eggs with sand to a depth of a few centimetres, however experiments have shown that the eggs are capable of developing normally and hatch as soon as currents uncover them again (Winslade 1971). Buried eggs experiencing reduced current flow, and therefore lower oxygen tension, can have delayed hatching periods which is considered a necessary adaptation to survival in a dynamic environment (Hassel et al. 2004).
110.
In a feeding study of larval assemblages in the southern North Sea, Pérez-Domínguez and Vogel (2010) found that the presence of larval sandeel was correlated with high levels of suspended particulate matter, including silt. The absence of silt in their stomach contents indicated that sandeel larvae were able to successfully target prey items in turbid environments.
111. Research by Behrens et al. (2007) on the oxygenation in the burrows of sandeel Ammodytes tobianus found that the oxygen penetration depth at the sediment interface was only a few millimetres. Sandeels were, however typically buried in anoxic sediments at depths of 1-4cm. In order to respire, sandeels appear to induce an advective transport through the permeable interstice to form an inverted cone of porewater with 93% oxygen saturation.
112. From the above, it is apparent that sandeel eggs, larvae and adults have a comparatively high tolerance to SSCs and sediment re-deposition but in view of their limited mobility and substrate dependence, the sensitivity of sandeels to these effects is considered to be medium.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 11 Fish and Shellfish Page 51
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