Safeguarding the Underwater Cultural Heritage of Stone Tidal Weirs on the Earth

The cross-cultural and multi-disciplinary study of stone tidal weirs and efforts to raise awareness require the establishment of an international network.

The academic core consists of the three member universities, part of the UNESCO UNITWIN Network for Underwater Archaeology: the Tokyo University of Marine Science and Technology, the University of Guam, and the University of Warsaw. The network enhances the protection and research efforts on underwater cultural heritage by connecting universities and professional training institutions, and acting as a bridge between academia, civil society, local communities, and policy makers. 

On the other hand, local NGO or NPO organizations play a central role in safeguarding or reviving stone tidal weirs. As an intermediary the academic core builds relationship between coastal community stakeholders, including NGOs or NPOs, and international organizations, including the UN, UNESCO, ICOMOS, plus local and national governments.

The UNESCO UNITWIN Network for Underwater Archaeology and the ICOMOS International Committee on the Underwater Cultural Heritage (ICOMOS-ICUCH) act on the implementation of the UNESCO Convention on the Protection of the Underwater Cultural Heritage, which in its Article 1-1 defines ‘underwater cultural heritage’ as all traces of human existence having a cultural, historical or archaeological character which have been partially or totally under water, periodically or continuously, for at least 100 years. 

All stone tidal weirs are partially or totally under water during certain periods of time. Almost all stone tidal weirs, or at least their bases, all over the world are likely to have been constructed more than 100 years ago. This Convention is the first international law which acknowledges stone tidal weirs as cultural heritage that needs to be protected.  Many countries have not ratified it and there is the need to continue to raise awareness on the Convention.

The underwater cultural heritage of stone tidal weirs was originally born as a local fishing mechanism. The processes are based on a rich local traditional ecological knowledge, which brought on by members of local coastal communities. Traditionally, local communities used stone tidal weirs twice a month during the spring tide; a custom that has been preventing overfishing by locals. At high tide they sometimes functioned as fishponds. 

The traditional ecological knowledge, for instance, on non-fishing periods, as well as that on fishery-related ritual activities such as beach opening ceremonies, is widely observed at coastal communities but it is rapidly disappearing before being recorded properly by anthropologists or archaeologists. As stone tidal weirs are easily broken by typhoons or high waves, frequent community-led repairing works based on traditional knowledge are absolutely needed. In case stone tidal weirs are abandoned, however, both communal spirit and traditional ecological knowledge would extinct.  

Stone tidal weirs are the most vulnerable against global climate change.  Recent field surveys and participant-observations of them prove that many stone tidal weirs have been abandoned or simply left broken, owing mainly to ocean environmental change.  If sea levels rise more than 1 meter, all stone tidal weirs on the earth do not function as fishing gear.   Once they are destroyed by storms or high waves, some coastal communities cannot afford to repair them, leaving simply them abandoned.  All over the world, indeed, the underwater cultural heritage of stone tidal weirs is in danger of closing down, as cultural heritage as well as traditional fishing gear.  For the purpose of understanding their vulnerability properly, the assessment of long-termed tidal range changes around stone tidal weirs, the measuring of coastal erosions faced by them, and the impact monitor of typhoons or high waves which destroy stone tidal weirs have been conducted, occasionally by help of remote sensing data.

Without doubt, stone tidal weirs contribute to marine biodiversity.  In comparison with intertidal zoneswithout stone tidal weir, those with stone tidal weirs have host diverse marine species.

Once stone tidal weirs are abandoned, the less fish is caught.  As the attention of local people shifts to destructive modern fishery,  all aspects connected to cultural diversity would also be disappeared.  In order to maintain coastal communities sustainable, they must not lose their biocultural diversity; stone tidal weirs could be served as an icon of such diversity as well. The UNESCO UNITWIN university network researches and studies how stone tidal weirs in safeguarding biocultural diversity.