Oka traveled the world gathering information about whaling practices including to Norway for harpoons, cannons and expertise.
He also established the first modern whaling company in Japan in 1899, Nihon Enyo Gyogyo K. which took its first whale on February 4, 1900, with a Norwegian gunner, Morten Pedersen.
On January 15, 2017, a helicopter in the Australian Whale Sanctuary photographed the Japanese whaling vessel Nisshin Maru with a freshly-killed minke whale on its deck.
Antarctic minke whale have experienced an apparent decline in population, though the International Union for Conservation of Nature (IUCN) indicates that it lacks sufficient data to confer a "threatened" designation on the species of minke whale.
Oka later became the first president of the Japan Whaling and Fishing Association, established in 1908.
In the early 20th century, Jūrō Oka dominated the whale meat market in Japan with assistance and instruction from Norwegian whalers and their leased or purchased ships.
Another boost was provided by the capture of a Russian whaling fleet and subsequent transfer to Toyo Gyo Gyo Co. As Japan's whaling industry expanded into new territory, including Korean waters, ship production and oil processing, Oka's company (renamed Toyo Hogei K.
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.