There is joy in discovery, particularly when the details are so surprising. I was similarly delighted to learn the source of hundreds of mysterious hash marks visible in aerial photographs of Tokyo Bay from 1956 (source). For reference, to the left of the question mark is Oi Racecourse 大井競馬場 / Tokyo City Keiba (map).
I’ll give you the answer quickly, courtesy of the Omori Nori Museum 大森 海苔のふるさと館 (map), which is located in Omori 大森, the section of Ota-ku adjacent to the original coastline . The museum has a large aerial photograph of Tokyo Bay which explains that these hash marks are fishing nets used in the farming of nori 海苔 (seaweed). The photo is so detailed we can see the small boats attending to the nets.
In addition to this wonderful photograph, the museum holds what is claimed to be the last nori boat in existence.
A little history
According to the museum, farming of seaweed came to the coast of Ota-ku circa 1700. The location was suitable for seaweed cultivation due to the shallow sea floor. Ironically, the shallow water eventually led to the demise of the industry: in 1962 it was agreed that the waters would become reclaimed to make way for the expansion of Haneda Airport; other locations were given up for the construction of the Tokyo Monorail; as Robert Whiting writes, “A seaweed field in Omori in Ota Ward, from which a prized delicacy, Omori no nori, had been harvested since the Edo Period (1603-1868), simply disappeared.”
Here’s a dramatic comparison of Tokyo Bay between 1960 and 2015 (source).
The following are several of the 1956 photos stitched together:
Older methods of nori farming
The Omori Nori Museum has a large painting of nori harvesting off the coast of Ota-ku. In the picture (below, second), one of Tokyo Bay’s daiba defensive islands is visible, in front of what I first assumed to be sea grass. These ‘grasses’, however, are evidence of seaweed farming.
Older methods of seaweed farming in Tokyo Bay (and other places) consisted of inserting bundles of bamboo into the ocean floor and allowing seaweed to accumulate on the bamboo branches. Some of the words related to this activity are explained in this helpful glossary:
- Takehibi 竹ひび / 竹ヒビ – bundles of bamboo used for attracting seaweed
- Kihibi 木ヒビ – bundles of tree branches used for attracting seaweed (possibly the Lithocarpus tree / matebashi マテバシイの木 / マテバシイ属)
- Furabo 振り棒（ふりぼう）: a stick with two handles and a sharp tip, used for making a hole in the sand into which the bamboo posts are placed (source)
This processes is depicted in an amusing and helpful diorama at the Omori Nori Museum:
As seen in the diorama, the seaweed farmer stands on stilts called 海苔下駄 nori geta ノリゲタ, which literally means ‘seaweed sandals’. The top of the norigeta is practically identical to the top of a regular geta 下駄 sandal.
This is what it used to look like in practice:
Seaweed Cultivation in Mikawa Bay 三河湾, Aichi (source)
Today, the old traditions of seaweed farming are occasionally practiced such as during that event near Kasai Rinkai Park 葛西臨海公園 in Edogawa, near Tokyo Disney (source):
After World War II, the old bamboo method of seaweed farming was generally replaced by the use of nets (second photo is captioned 海苔網 ‘seaweed nets’):
Seaweed (Nori) Aquaculture on the Ota-ku coast at its peak, 1959 最盛期の大田区沿岸の海苔養殖漁場
Although seaweed farming is no longer practiced off the coast of Ota-ku, there are places all over Japan where it continues. I was excited to catch a glimpse of it in action in Nagasu, Kumamoto Prefecture (Kyushu) (map):
The Ota-Ku Local History Museum 大田区立郷土博物館 also has a room dedicated to the history of Ota-ku’s nori farming; it overlaps with the Omori Nori Museum, but it’s worth a visit. Seen here is a map of the nori farming locations superimposed over the location of the expanded Haneda Airport. Also shown here are nori farming artifacts and photos.
- Drying seaweed in Kiba, Koto-ku (Twitter)
- Takehibi in Funabashi (website)
- Kawasaki Nori-making Materials Design Room 川崎の海苔づくり資料室 (website) (PDF) (map)
- Odaiba, then & now: a visual history お台場の歴史
- Tokyo reclaimed land map 東京都の埋立地地図