Use stream of consciousness to answer the following. The Japanese river otter (Lutra lutra whiteleyi) ( , Nihon-kawauso) is an extinct variety of otter formerly widespread in Japan. Dating back to the 1880s, it was even seen in Tokyo. The population suddenly shrank in the 1930s, and the mammal nearly vanished. Since then, it has only been spotted several times, in 1964 in the Seto Inland Sea, and in the Uwa Sea in 1972 and 1973. The last official sighting was in the southern part of Kochi Prefecture in 1979, when it was photographed in the mouth of the Shinjo River in Susaki. It was subsequently classified as a "Critically Endangered" species on the Japanese Red List. On August 28, 2012, the Japanese river otter was officially declared extinct by the Ministry of the Environment. It is the official animal symbol of Ehime Prefecture. In February 2017, a wild otter was caught on camera on Tsushima Island, Nagasaki Prefecture. However, it is not known whether the observed otter was a Japanese river otter.

Answer this question based on the passage: when did the japanese river otter become extinct?
To answer the above question, the relevant sentence is: On August 28, 2012, the Japanese river otter was officially declared extinct by the Ministry of the Environment. Final answer: August 28 , 2012.