2007:494 - DUBLIN: Spencer Dock, North Wall Quay, Dublin

Monitoring was undertaken according to the programme of works on site. The first phase was undertaken by Franc Myles (see No. 493, Excavations 2007) and, as bulk excavation progressed to deeper levels, worked wood and the remains of fish trap structures were identified in the estuarine silt. The licence was transferred to the writer, who directed the archaeological excavation of this material.

Excavation uncovered the remains of two stationary fishing structures or fish traps constructed of wood and several pieces of worked wood which had been washed in by the tide.

The traps may be described as ebb weirs. These structures were generally V-shaped and were constructed of large wooden fences or stone walls. They were erected in tidal zones and caught fish that drifted with the falling tide. There was often a basket at the junction of the fences. The fences served to direct the fish into the basket or trap. Fish could then be removed when the traps were exposed for two to three hours at low tide.

All of the wooden remains had been covered in layers of estuarine silt, which had built up from tidal deposition. These waterlogged silt deposits facilitated the preservation of the wood.

Two distinct phases of prehistoric activity were identified on the southern end of the site, within the area previously occupied by the Liffey estuary.

Phase 1 was represented by the in situ remains of a fish trap, most probably an ebb weir, which was partially exposed within an area of deeper excavation (to minus 4.66m OD) on the southern end of the site. At this location the trap would have stood in the intertidal mudflats along the northern edge of the River Liffey or on the shore of an island within the estuary area. The remains of this trap were dated to the Late Mesolithic period (6000–5760 cal BC).

Phase 2 was characterised by the remains of a wattle panel which was probably part of the fence of a much larger ebb weir. The wattle panel was not in situ but was found washed up against what was then the shoreline of the Liffey estuary. The weir probably would originally have stood in the intertidal mud flats somewhere to the south of the shore. It was dated to the Middle Neolithic period (3630–3370 cal BC).

Late Mesolithic
The Late Mesolithic remains were defined by two linear stake rows (F300 and F301), which probably represent the remains of a single fish trap. The western stake row, F300, was oriented north-east/south-west and the eastern stake row, F301, ran north-west/south-east. The excavated portions of these fences were set 8.47m apart. The two stake rows would probably have joined at a point further north, where there was likely to have been a basket trap. The area to the north of the stake rows did not require excavation to the same depth and consequently no further remains of this fish trap were uncovered. The stakes were set an average of 0.25m apart and were an average of 0.03m wide. They varied considerably in length, ranging from 0.03m to 1.15m, indicating that they had been driven into the silt at various depths.

There were fifteen stakes within the western row F300, which extended for 4.45m, and the eastern fence of F301 comprised a longer (12.75m) staggered row of 62 stakes. The majority of stakes were identified as hazel, but there were a few pomaceous fruitwoods. The hazel pieces ranged between three and seventeen years and the pomaceous fruitwood types ranged from seven to 24. Several stakes had worked ends. These took the form of wedge-shaped points (cut on two sides) and chisel points (cut on just one face). All of the worked pieces were cut at angles of 10°. The majority had flat facets but there were also several concave examples. The facets ranged from 15mm to 52mm in length, and from 7mm to 23mm in width.

Middle Neolithic
A second phase of activity was identified at a higher level (between minus 2.4m OD and minus 3.01m OD), where the remains of another fish trap were uncovered on the east end of the site. This trap comprised the remains of a wattle fence, which was beautifully preserved. The surviving remains of Fish trap 1 measured 4.41m long and 4.16m wide. They were found lying almost horizontally, having been washed up on the shore, but would almost certainly have been part of a vertical fence. That fence would have formed part of a much larger fish trap structure, most probably an ebb weir.

The wattle panel was woven from a series of rods and sails that were originally supported by four upright stakes. The panel was secured to the stakes by a series of hazel withies, some of which were incorporated into the weave. As already mentioned the panel was found lying horizontally but would almost certainly have stood vertically and the stakes would have held it in position. The sails and stakes were the upright components of the trap and the rods and withies formed the horizontal weave. The stakes ranged between 1.42m and 2.03m in length and were 0.05m wide on average. They were all made of hazel pieces that ranged between nine and 28 years. The sails ranged from 1.63m to 3.16m long and were an average of 0.02m wide. A sample of these were identified to species and all were found to be hazel that was between two and seven years old when cut. Seven horizontal rods were woven into the structure of the fish fence. The rods were an average of 0.03m wide and were secured to the stakes and to some of the sails by a series of knots. A total of sixteen knots had been tied at a number of key points within the structure, where they were bound around stakes and sails.

No finds or fish bones were recovered during excavation.

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