Though the Japanese population of Great Cormorants Phalacrocorax carbo has increased in recent decades, information on its spread to the northern island of Hokkaido has not been reported outside of Japan. The purpose of this paper is to update the scientific community about the distribution and breeding ecology of Great Cormorants and to provide comparative information on the abundant and phenotypically similar resident Japanese Cormorant P. capillatus. Several ornithological groups and researchers were contacted in order to gather information about the current distribution and breeding activity of the Great Cormorant in the region. This paper consolidates the findings of Japanese research groups, translated publications and direct observations.