Oka traveled the world gathering information about whaling practices including to Norway for harpoons, cannons and expertise.
Whalers would spot whales from stations along the shore and launch boats to catch them with harpoons and lances.enforcement of the Shorui-Awaremi-no-rei (ordinances of animal protection) excluded whales due to being perceived locally as fish, despite the fulfillment of terms of protection for having "mammalian natures", and that a paper regarding whales as mammals was published in Kyoto in 1758.As a precept, Buddhists and other concerned people created folklore tales about whaling communities and those who practiced whaling on an industrial scales met tragic downfalls by supernatural phenomenon such as phantoms and the curses of whales.When they kill whales, hunters invoke the Buddha and pray for the repose of whales' souls; they held funerals for whales, built cenotaphs for them, gave posthumous Buddhist names to them, and when a dead fetus is removed from a butchered cow, an effort is made to release it into the sea.These practices are intended to encourage emotionally healthy or spiritual relationships with whales, and are connected with Japanese religious beliefs.The incident effectively marked the end of traditional Japanese whaling practice.
Norwegian-style modern whaling, based on the use of power-driven vessels, cannons and exploding harpoons, was introduced in the Meiji period largely through the efforts of Jūrō Oka who is considered the "father of modern Japanese whaling".
This decline of coastal stocks resulted not only in financial solvency of many industrial groups but also in disputes between feudal domains in western Japan that required the intervention of the shogunate.
As early as the Edo Period, Japanese writers may have tried to call attention to overkill by American and Norwegian whalers, whose hunting practices led to depletion of whale populations, and the tragedy called Semi-nagare, an incident in which over 100 Taiji whalers were lost in the ill-timed pursuit of the only two whales they had seen in December 1878.
There harpooners would approach in four boats of their own.
The nets made escape more difficult and, in its struggle to escape, the whale got tired sooner.
Blue whales, sei, Bryde's and sperm whales were however also taken when possible.