stone tidal weirs of japan

By Heather Earle and Cynthia Neri Zayas

Ancestral Connections & Geographic Extent Temporal Extent Biophysical Manipulations Target Species Ceremony & Stewardship Current Status

Stone tidal weirs were constructed and used extensively by the Japanese across the islands of western and southern Japan (Iwabuchi 2014), extending as far south as the Yaeyama islands east of Taiwan (Akimichi 2012). Depending on the region, these weirs take on a variety of names. Around Kyushu island, and the small adjacent islands of Western Japan, there were more than 200 weirs in the early 18th century, which are known as ishihibi or sukki (Iwabuchi 2014). Further south, in the Okinawa islands, there are approximately 100 weirs which are referred to as kaki (Iwabuchi 2014).  They are also called uoagaki (fish wall) and individual weirs will often carry their own particular names, derived from geographical location as well as kin-groups (Akimichi 2012). 

There is limited documentation on how long stone tidal weirs have been used and cared for in Japan. Several authors refer to them as “ancient” in origin (Nishimura 1981; Akimichi 2012). Nishimura (1981) notes that a considerable number of poems referring to the stone weirs are found in the Omoro Sōshi, an anthology of ancient poems from the Okinawa and Amami Islands, spanning the time period from the 12th to 17th centuries. Iwabuchi (2014) notes that an abundance of weirs (approximately 200) were in use in Ariake Bay on Kyushu Island in the early 18th century.

Stone tidal weirs in Japan are typically constructed of stone and coral, typically between 25 and 80 cm high and 40 - 150 cm wide extending for hundreds of metres in the shallows along the shore (Akimichi 2012). The weirs vary in shape, depending on the region in which they were built (Nishimura 1981), although most have a semi-circular shape (Akimichi 2012).  As with other tidal weirs around the Pacific, Japanese weirs passively trap fish with the rising and ebbing of the tides: as the tide retreats, the water level descends below the height of the wall, trapping fish which can then be easily harvested (Akimichi 2012). Sometimes there is a central gate called a futikakii (literally, mouth wall) in the central part of the weir, which allows fish to enter from deeper waters during a rising tide, but traps them during an ebb tide (Zayas 2019). 

Japanese stone tidal weirs likely target a variety of fish as well as benthic invertebrates (Zayas, personal communication). Mullet (Mugil cephalus) are a common species in Japanese weirs, with the most famous weir in Ariake Bay called the ‘Mullet Tidal Weir’, which caught ‘innumerable’ mullet in 1881 (Iwabuchi 2014).

Constructing and maintaining stone tidal weirs requires considerable effort and was often carried out collectively and voluntarily by a community (Akimichi 2012). Sometimes a weir would be managed by particular individuals and kin groups (Akimichi 2012; Zayas 2019) although more typically they were communally owned and managed as part of  a local commons known as sato-umi or satoumi, literally translated as “the sea of the village community” (Akimichi 2012).  Within the concept of sato-umi, it is understood that the productivity of these innovations depends on the flow of resources between forest, river, and sea via water. This understanding guides human behaviour within these social-ecological systems, and positions people to contribute to the productivity of the system while also being sustained by it (Akimichi 2012).   

Ritual offerings of harvest occurred annually (Zayas 2019) with the first catch typically offered to the community’s sacred shrine (utaki or ugan) (Akimichi 2012) in tandem with other gifts such as fruit, desserts, and harvests from the kitchen garden. Sometimes fish were buried underground and accompanied by prayers for a year of good catch (Akimichi 2012).

Most of the weirs across Japan have fallen into disrepair and disuse (Akimichi 2012; Iwabuchi 2014; Zayas 2019). There are several possible factors contributing to this including declining catch due to commercial fisheries, the decline of communal labour practices and out-migration from coastal villages, and a transition to more modern methods of fishing (Akimichi 2012; United Nations University 2011). Stone tidal weirs require regular maintenance as they are frequently damaged by wave action during the annual typhoon season (Nishimura 1981).

Some weirs are still in use (Zayas 2019) and several have recently been restored in the Yaeyama Islands (Akimichi 2012). While many are no longer in use as a component of local food systems, they are often restored as heritage sites. In Ishagaki Jima, the Ryukyus schools and surrounding communities maintain the fish traps as a teaching tool for biodiversity and conservation. Akimichi (2012) suggests that these weirs may be emerging “as a symbol for the conservation of the marine environment into the twenty-first century”.  In 2010, The World Ishihimi summit was held in Shiraho, Japan with the goal of uniting practitioners and knowledge holders from all around the world to share their experiences and approaches. The rights to harvest from the weirs were transferred to private property owners through the Fisheries Law after the second world war (Zayas 2019).

References

Akimichi, T. 2011. Changing coastal commons in a sub-tropical island ecosystem, Yaeyama Islands, Japan. Pages 125–137 G. Baldacchino and D. Niles (eds.). Island Futures. Springer Japan, Tokyo.

Iwabuchi, A. 2014. Stone Tidal Weirs, “Underwater Cultural Heritage or Not?” Pages 1-12 Van Tilburg, H., Tripati, S., Walker Vadillo, V., Fahy, B., and Kimura, J. (eds.), The MUA Collection, accessed December 29, 2021, http://themua.org/collections/items/show/1623.

Nishimura, A. 1981. Maritime counterpart to megalithic culture on land. Journal de la Société des Océanistes 37:255–266.

United Nations University Institute of Advanced Studies Operating Unit Ishikawa/Kanazawa. 2011. Biological and cultural diversity in coastal communities, exploring the potential of Satoumi for implementing the ecosystem approach in the Japanese Archipelago. Secretariat of the Convention on Biological Diversity, Montreal, Technical Series no. 61.

Zayas, C. N. 2019. Stone tidal weirs rising from the ruins. Journal of Ocean and Culture 2:88–109.