Gwynedd Archaeological Trust
Regional Historic Environment Record

Fish Wier, Gorad Ddu

Primary Reference Number (PRN) : 7220
Trust : Gwynedd
Community : Llanfair Pwllgwyngyll
Unitary authority : Ynys Mon
NGR : SH54457151
Site Type (preferred type first) : Unknown FISH WEIR
Status : Scheduled Ancient Monument

Description :
A possible fish holding pool 4-5m across, associated with Gorad Ddu? <1>

Gorad Ddu centred at NGR SH54657160 is located on the northern shore of The Swellies region of the Menai Straits between the Menai Suspension Bridge and Britannia Tubular Bridge (Fig I). It is situated in a typical location with a large expanse of ground left uncovered at low water. This type of construction is probably the most sophisticated stone built fish trap used in Britain (Jones 1983, 30). Gorad Ddu is described as shown in Fig 2 from west to east.

The west wall of the weir extends at right angles to the shore for 70m before it curves to the east and terminates at the west side of the sluice. The southern, seaward, end of this wall is of similar massive construction to the main wall of the weir but becomes less substantial as it approaches the shore and in places is difficult to locate. There is a 2m breach in this western wall located 5m west of the sluice through which electricity cables were laid to Ynys Gorad Goch in 1997 (Plate 4). The wall was reinstated at the time but the standard of construction obviously could not withstand the forces of the sea at this point. The stones have tumbled mainly to the seaward side of the wall and the damage would appear to be continuing.

The angle at the west end of the weir is known as the ' cod-end' where the fish were trapped and caught (Plate 2). A well-built sluice is located in the wall at this angle that allowed the water to escape but would have restrained the fish . The sluice may have been rebuilt several times during the working life of the weir, as the stone dressing is much finer than the rest of the wall. The east side of the sluice has a 'U' shaped groove 0.2m wide by 0.3m deep (Plate 3). This could have held a device for holding back the ebb tide so that the fish were confined in a pool to the north but it was more usual for the ·cod-end' to contain a device for holding the fish. In this case the sluice would have contained a wattle or wooden lathe sluice gate, although sometimes nets or baskets were employed to hold the fish (Davis 1958, 25). Lewes states that iron grating was used in the 18th century in this context (Lewes 1924, 399). The west side of the sluice appears to have slumped and no groove was visible.

The main wall of Gorad Ddu, running for 96m parallel to the shore, is up to 3m high in places and extends a further 0.45m into the silts (Plate I). It is 2.5m wide at the top and 3m wide at the bottom with a foundation plinth I m wide visible along the north side of the wall for a distance of 43m. The dry-stone walls have two well-defined faces with a fill of smaller stones. The eastern end of this main wall curves to join a rocky outcrop where the wall peters out and the outcrop itself becomes the barrier.

There are two areas of collapse on the seaward side of this main wall. One occurs 5m to the east of the sluice and extends along the wall for 7m and the other, 15m to the east of the sluice extends for !I m. Both are, at present, confined to the outer face of the wall and the collapse spreads up to 3m from the base of the wall. The inner face of the wall at these points remains intact but is obviously vulnerable to storm or current damage.

The rocky outcrop forms the barrier for the weir for 55m. The outcrop is c. 75m in diameter with a high point on the southern edge that is only inundated by very high tides. The northern side of the outcrop merges into the shoreline. There are several small stretches of walling roughly in line with the rest of the weir, on the outcrop itself. One occurs just west of the summit of the outcrop and consists of single line of large boulders set on edge between two natural small cliffs. The other also spans a gap between two natural small cliffs but is of similar dry-stone wall construction to the rest of the weir and is 2m long x lm wide x lm high. On the summit of this natural outcrop is a rectangular scoop that appears to have been artificially cut out of the rock. It is 3.5m long and 2.5m wide and may once have had a structure built within it.

Towards the southern side of the outcrop is a natural channel 65m long which appears to have been artificially widened and deepened, particularly at the eastern end where it forms a gully 6m wide. This is a significant feature as, without this channel, fish would not have been able to enter the pool within the main part of the weir.

The weir wall continues from the east side of the outcrop for a further 80m towards Ynys Welltog. The wall here is not as substantial as the main wall to the west of the rock outcrop but is still well built. There appears to be a definite termination at the eastern end although the wall is only 0.5m high and it could indicate an earlier breach. There are two areas of collapse on the north side of the wall close to the rock outcrop. They both extend for I Om, the first adjoining the rock outcrop and the second occurring 2m further east. The walls of Gorad Ddu are all of dry-stone construction allowing the ebbing tide to pass through. The interstices are too small to allow fish to pass through but provide habitats for small fish and fry which are preyed upon by larger ones (Jones 1983, 30). The walls are also festooned with seaweed, which account for it being referred to as Gorad Ddu or Black Weir. The seaweed is mainly Ascophyllum nodosum although Porphyra umbilicalis is also found on the walls and surrounding rocks which may have been harvested for ' Iaverbread'. (Richards, 1998).

Sources :
Derby, S. , 2017 , By investigating the conception, design, and ultimate failure of the Britannia Park venture, can we evaluate the potential significance of this site in mid-19th century Caernarfonshire?
Richards, A. , 1998 , Coastal Erosion Project: Fish Weir Survey ( © GAT)
Jones, S. , 1997 , Coastal Erosion Survey - Anglesey , <1>
Jones, C. , 1983 , The International Journal of Nautical Archaeology & Underwater Exploration , <3>

Events :
40362 : Coastal Erosion Survey: Anglesey (year : 1997)
40412 : Fish Weir Survey (year : 1998)

Related PRNs :

Compiled date : 16-05-1997

The above data are supplied by GAT in partnership with its Local Authorities (Anglesey, Conwy and Gwynedd County Councils, and Snowdonia National Park Authority), © GAT 2018 (and in part © Crown, 2018 - as indicated)
This information is supplied for the purposes of personal interest only and may not be used as part of a commercial project.

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