In 1787 he visited the mainland coast of Korea then crossed over to Oku-Yeso (Sakhalin). La Pérouse was enthusiastic about the people of Sakhalin and their friendliness:
“Since leaving France, we had not encountered others, who so excited our interest and admiration… It went against our preconceived ideas to find among a hunting and fishing people, who neither cultivated the earth nor raised domestic animals, manners which were in general more gentle and grave -and who perhaps had greater intelligence- than that to be found in any European nation.”
The inhabitants had drawn him a map, showing their country, Yeso (also Yezo, now called Hokkaido) and the coasts of Tartary (mainland Asia). La Pérouse wanted to sail through the channel between Sakhalin and Asia, but failed, so he turned south, and sails through La Pérouse Strait.
The La Pérouse Strait is a strait dividing the southern part of the Russian island of Sakhalin (Karafuto) from the northern part of the Japanese island of Hokkaidō, and connecting the Sea of Japan on the west with the Sea of Okhotsk on the east. It is 40 km (25 mi) long and 20 to 40 m (66 to 130 ft) deep.
Japan’s territorial waters extend to three nautical miles into the strait instead of the usual twelve, reportedly to allow nuclear-armed United States Navy warships and submarines to transit the strait without violating Japan’s prohibition against nuclear weapons in its territory