expected from mining, dredging and similar operations. Herring eggs have been recorded to successfully hatch at SSCs up to 7000mg/l (Messieh et al. 1981).
102. Fine silt particles associated with increases in SSCs have the potential to adhere to the gills of larvae which could cause suffocation (De Groot 1980). Griffin et al. (2009) suggested that larval survival rates could be reduced at SSCs as low as 250mg/l. Larvae of most fish species are visual predators therefore, if visibility is reduced as a result of SSCs, this may impact foraging success (Johnston and Wildish 1981). Herring, plaice, sole and cod larvae sight prey at a distance of only a few millimetres (Bone and Moore 2008). There is evidence to suggest however that SSCs may enhance feeding rates by providing a visual contrast to prey items on the small perceptive scale used by the larvae. In addition larvae may be subject to reduced predation from larger visual planktivores in turbid environments (Bone and Moore 2008).
103.
In a study which exposed Pacific herring Clupea harengus pallasi larvae to suspensions of estuarine sediment and volcanic ash at concentrations ranging from 0 to 8,000mg/l, Boehlert and Morgan (1985) found that maximum feeding incidence and intensity occurred at levels of suspension of up to 500mg/l above which feeding activity decreased.
104. Herring eggs and larvae are considered to be the most sensitive to increased SSCs. It is therefore considered that they represent the worst case and that eggs and larvae of other species are of lower sensitivity. The sensitivity of herring eggs and larvae is taken as medium. Taking the low magnitude, the impact of increased SSCs on fish eggs and larvae is assessed to be of minor adverse significance.
11.6.1.2.2 Physiological Effects on Shellfish Species 105. Berried crustaceans e.g., brown crab and lobster are likely to be more vulnerable to smothering as the eggs carried by these species require regular aeration. However, as females of these species are ovigerous the potential for eggs to be impacted by increased SCCs/sediment re-deposition would be partially influenced by the response/tolerance of the adult to these impacts. Marine Life Information Network (MarLIN) sensitivity scores to increased suspended sediment concentrations and smothering are assessed as low for edible crab, which is in part due to their mobile nature. Taking a precautionary approach, a medium sensitivity has been assigned for shellfish as a whole, including whelks.
106. As stated above, the magnitude of effect for the installation of the East Anglia THREE windfarm site and the offshore section of the offshore export cables is considered to be low. The magnitude of effect for the installation of the offshore export cables in
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 11 Fish and Shellfish Page 50
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