2015:253 - Fishtrap Feature FT3, Castlemaine Harbour, Kerry

Archaeological investigation took place of a fishtrap feature (Feature FT3) located within Castlemaine Harbour, Co. Kerry. The work was undertaken by ADCO as part of the pre-planning requirement for a proposed marine aquaculture project developed by Bórd Iascaigh Mhara (BIM). Feature FT3 is located within the intertidal zone, situated opposite Aghuils Townland, on the northern side of Castlemaine Harbour. A fishtrap at this location is first recorded on the OS First Edition Map of 1841, annotated ‘Salmon Weir’, although it is absent from any subsequent mapping. The archaeological survey and associated precision mapping identified the presence of nine vertical timbers (soft-wood) associated with the shore-fence component of the structure. These were found partially exposed on the seabed (protruding <40mm), aligned north-east/south-west between ITM: 471757E, 601962N and ITM: 471827E, 6001865N. Some limited excavation around the timbers was required to allow accurate recording to take place. A detailed photographic and written record was made and the timbers were positioned-fixed in three dimensions using a Topcon DGPS unit. In addition, a digital terrain map (DTM) and contour map of the seabed was generated to provide a detailed account of seabed topography, allowing the relationship between the fishtrap structure and the surrounding seabed to be examined. A metal detection survey was also undertaken to establish the presence of any metallic material that might be related to the structure. While positive identification of structural timbers from the flood-fence and/or ‘Eye’ component of the fishtrap remains unconfirmed, a number of indicators would point to their in situ preservation. Firstly, the seabed topography rises across these areas, providing a greater potential burial-depth than present for the shore-fence location. In addition, a well-established mussel-bed provides blanket-cover of the seabed across the ‘Eye’ area. As such, it is likely that the flood-fence and ‘Eye’ components remain buried at a greater depth within these seabed deposits. Moreover, when comparing the cartographic information from the OS First Edition map with the most recent survey data, both the cartographic depiction and existing fence-line were found to overlie each other with a considerable degree of accuracy, in turn suggesting that the OS mapping is a reliable depiction of the fishtrap’s true extent. A narrow ridge of sand is located parallel to the line of identified fishtrap timbers, at a point 2.4m (min.) to the east, and may have an association with the structure. The ridge extends the entire projected length of the shore-fence and measures 0.08m in height and 3.3-4m in width. Another, less-defined feature extends at right angles to the aforementioned sand ridge, on the northern side of the projected line of the flood-fence (at a point 9m to the north). This deposit measures approximately 8m in width, 0.06m in height, and extends 100m+ to the south-west. Both of these sand features are clearly visible on the OSI Orthophotography of 2005. Comparison of their current extent with that shown in 2005 shows some variation, their extent and alignment being subject to change over time. It remains unclear what association these natural features might have with Fishtrap FT3, however, it is probable that they are the result of a localised hydrodynamic change instigated by the presence of the fishtrap structure. ADCO recommended that an exclusion zone, as detailed in the archaeological report, be placed around the known and probable extent of the fishtrap site, measuring no less the 30m from the nearest point in all directions. The investigations were undertaken on 13 October 2015.

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