Cambaroides japonicus has been assessed as Data Deficient. While this species is threatened by competition with the invasive Signal Crayfish (Pacifastacus leniusculus), and associated crayfish plague, there is currently uncertainty over this species extent of occurrence and the number of locations in which it is found. With a restricted distribution and low number of locations this species could be classified under a threatened category; however further research is needed to determine the extent to which this species is impacted upon by the presence of the Signal Crayfish, and to determine its extent of occurrence before a more accurate assessment of conservation status can be made.

This species is indigenous to northern Japan, and is found in Hokkaido, Aomori, Akita, and Iwate Prefectures (T. Kawai and Y. Machino pers. comm. 2009).

There is no current population information available for this for this species. This species was considered common in Hokkaido until the twentieth century; however following the introduction of the Signal crayfish in the 1920s and habitat destruction since the 1960s C. japonicus populations have continued to decline, and the species is thought to be rare in Hokkaido (Y. Machino pers. comm. 2010).

This species inhabits swift or high gradient streams without fish, and is associated with abundant cover in dense broadleaf forests. This type of habitat serves as a conservation area, and consideration of riparian composition may facilitate conservation efforts (Usio 2007). This species will carry 30-100 eggs and grow to approximately 8 cm (T. Kawai and Y. Machino pers. comm. 2009).

This species is threatened by interspecific competitor from the invasive Signal Crayfish Pacifastacus leniusculus. Pacifastacus leniusculus is competitively advantageous, and has a markedly higher reproductive ability in terms of egg numbers (Nakata, Tanaka and Goshima 2004). Fewer eggs, more larval stages, slower growth, smaller pereopods, and poor disease resistance all contribute to the displacement of indigenous populations of this species by introduced competitors such as P. leniusculus. The fecundity of this species is an order of magnitude lower than that of P. leniusculus (Yamanaka, Kuwabara and Shio 1997).

In the past, this species had a widespread distribution in Hokkaido (Kawai 1996), but the population has drastically declined, prompting the Japanese Fisheries Agency in 1998 and the Environmental Agency in 2000 to declare it an endangered species (Nakata, Tsutsumi, Kawai and Goshima 2005, Usio 2007). Crayfish plague may be a factor in species displacement in some Hokkaido rivers and lakes, though there is yet no evidence of infection in this prefecture but it should be investigated further (Usio, Motoharu and Shigeru 2001).

This species is commercially harvested for human consumption, both from wild and captive populations.

This species has been listed as an endangered species by the Japanese Fisheries Agency in 1998 and the Environmental Agency in 2000 (Nakata, Tsutsumi, Kawai and Goshima 2005, Usio 2007). Protection measures, such as education and awareness, particularly in schools, have been initiated; however further efforts are necessary, such as new protection measures and policy to prevent further declines (Y. Machino pers. comm. 2010). Further research on the threat from the Signal Crayfish, and monitoring of populations trends is recommended.