This fish trap was identified during RCAHMW aerial reconnaissance in 2003. consists of three walls, two of which are connected to Ynys Tobig. Traces of both are visible on 2nd and 3rd edition OS mapping. The first wall is connected to the southwest tip of the island and extends in a southwesterly direction for some 33m tracing a right angle and another angled turn before fading out. The second wall extends from the island's northeastern tip and runs in an easterly direction for about 15m. Together with the second wall, the third wall begins by forming a funnel shape, with its apex pointing seaward. After some 15m the wall turns sharply north, and extends approximately 60m in a northerly direction until it terminates at Ynys Gaint.

Sources include:
National Assembly of Wales, 2009, vertical AP
Ordnance Survey, 1899, 2nd edition Landmark
Ordnance Survey, 1914-25, 3rd edition Landmark
RCAHMW, 2003, oblique aerial photographic coverage, 2003-cs-1180; 1186. 2003/5085-48.

Maritime Officer, RCAHMW, January 2011.