Sea stone - Kaijōkoku

…A type of miscellaneous tax in early modern Japan, also called umikoku or umijoishi. In the early Edo period, villages along the sea or river estimated their harvests from fishing, hunting and gathering seaweed in the sea and river, and included this in their village tax just like fields.

*Some of the terminology that refers to "sea stone" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…近世日本の色高(雑税)の一種で，海石（うみこく），海上石ともいう。江戸初期，海川付けの村が海川で行う漁猟採藻の収獲高を見積り，それを田畑同様村高に結んだもの。…

※「海上石」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報