Off the coast of Japan, the distributions of the Shiho and Naisa types are well-documented and largely nonoverlapping, with the Naisa-type inhabiting the warm-temperate waters of the Kuroshio Current, and the Shiho-type inhabiting cold-temperate waters of the Oyashio Current. Some evidence suggests these populations might even be distinct subspecies, based on differences in morphology, mitochondrial DNA and breeding seasons. Beyond Japan, the Naisa-type occurs in southeast Asia, the Indian Ocean, and Hawaii, and the Shiho-type can be found in the California Current and off Peru.