An ancient fish trap in its present condition at Llygwy Bay, Anglesey in north Wales that is located near to a settlement thought to date from around AD 300. Fish that swim over the wals of the trap at high tide are trapped as the tide recedes, whereupon they are easily collected by hand at low-water. Jennings,S., M.J. Kaiser, and J.D. Reynolds. 2001. Marine Fisheries Ecology. Blackwell Science, Malden, MA. 417 p.