The report about Sea-lion hunging on Takeshima dates back to two weeks before the famous Battle of Tsushima which almost ended around Takeshima on 28th May 1905. This is one of the good evidence not only that incorporation was not "secret" at all, but also people of Shimane has already know the fact of incorporation very well.
"●Sea-lion Hunting on Takeshima
As you readers have already know, Takeshima is a solitary island far off in the sea which locates 85 sea-ris north-west of Oki country and one of the island is around 20-chou(町), the other is merely aounrd 12-chou. Mr. Nakai Yonesaburo first voyaged tothe year before last and found the colony of Sea-lion. He found it is a pity that the island is omitted from the sea-chart, and petitioned to the national government. Through the good offices of Mr. Nakai, the islands were determined as the territory of the empire and incorporated into our Shimane prefecture by the Prefectural Order on 22 Feb. Ths islands are, as were described above, a meeting place of sea-lions for three months from May to July. Now apart from Nr. Nakai, three more rivals has emerged. Then they publised the licence only to those four and is going to let the four to hunt cooperatively. Furthermore, from what I hear, the period of time above are the period of their deivery, so the female are on the land for nurcing the baby, and male also land for the love of female. This is convenient for hunting. 7-8 thousand of sea-lion are on the same zone, tops, but excessive hunting would damage their reproduction. So the number of hunting is limited to 6-7 hundred per year so that they would make a profit for 5-10 years."
The article says the man's name was Yonesaburo, but it is Yozaburo or Yosaburo, in fact. San-in Shimbun(山陰新聞) is a local newspaper in Matsue, and now it called San-in Chuo Shinpo(山陰中央新報).
The article was founded and provided by Mr. Magic Eye, who is a good researcher and a collector of those historical stuff. Thank you for sharing a good information with us !