AN EXTENSIVE tidal weir complex close to Barna and a late medieval quay on Mutton Island have become the latest in a series of recent archaeological finds in Galway Bay.

The finds are “transforming our knowledge” of a “neglected aspect” of Connacht’s maritime history, according to Connemara archaeologist Michael Gibbons.

The tidal weir complex in Rusheen Bay, to the west of the city, is visible at low tide and appears as a series of stone rapids across a fast-flowing tidal race mouth, Gibbons says.

It is not far from the location of the earliest discovery to date in that area – the 6,000-year-old Barna boat which has been conserved for display at Galway Atlantaquaria in Salthill.

A barrier of “granite erratics” at the weir complex has been adapted by hand, with several large channels cut through an 80-metre-wide band of rock.

The stone-faced channels are “designed to control the flow of water in and out of the lagoon to the north of it”, Gibbons says.

They represent a “sophisticated response to the problem of manipulating the large volumes of water that run in and out of the enclosed bay on a daily basis”.

Their presence implies that a considerable stock of fish, possibly herring, migrated through the complex and into Barna river, he suggests. One of the channels may also have been used as a tidal mill, although none of the super structures is currently visible. The complex may date to the early Christian period.

A series of monuments and structures, including a pre- Christian estuary midden, overlook the location. The remains of a large fort of about 140 metres in diameter are on a ridge close by.

The fort, which may date to the Iron Age, could have given its name to the townland, Cnoc na Cathrach – Knocknacarra – now one of Galway city’s largest suburbs. A mill dating to AD 600 was found about 40 years ago on a stream which feeds Rusheen estuary.

Further east, a medieval quay at Mutton Island, location of a lighthouse and sewage treatment plant, was discovered by Galway city heritage officer Jim Higgins.

It predates the current lighthouse quay and may be linked to a series of fortifications built in the 17th century, according to Gibbons. The forts were demolished to accommodate construction of the lighthouse in the early 19th century.

The finds illustrate the extensive and diverse range of Galway’s maritime heritage, Gibbons says. Other recent finds already reported have included a medieval harbour at Cill Éinne on the Aran island of Inis Mór and a 17th-century harbour on Inishbofin island.

He and colleagues have also found a dog whelk midden site dating to the Iron Age at Culfin Bay, near Renvyle. He says there may have been an extensive dog whelk trade along the Galway and Mayo coasts in early Christian Europe.

He has also found a series of large fish traps at Béal a Dangan and on the Errislannan peninsula near Clifden, and a fish “palace” on the edge of the Claddagh in Galway city, where pilchards were pressed for oil.

More than 200 vernacular quays and slips along the Connemara coast have already been recorded, reflecting the extent of the kelp “boom” in the 18th and 19th centuries.

Some 77 of these were recorded on Inishnee island alone, according to Mr Gibbons.

The quays helped to sustain one of the most dense rural populations in 19th-century Europe at the time, but came at a “high environmental cost”, as they facilitated “the massive destruction of the coastal bogs which once were a feature of this landscape”.