suction dredging

Has anyone managed to find anything on suction dredging at depths of 300m? All I've found is material that indicates it is only possible at a little over 100m depth.

e.g.

http://www.vanoord.com/webfront/base.asp?pageid=192#


I see BON asserts that "current marine mining and dredging technologies can cope with depths of 600m". However, I don't see how it could be by suction dredging.

Animated Film clip here of a suction dredger at work.

http://www.vanoord.com/webfront/swf/vanoord_player.asp?vom=http://www.vanoord.com/public/Downloads/Movies/3D_animaties/Volvox%20Olympia_flv_512kbit.flv