The rediscovery of Oncorhynchus kawamurae, Kunimasu: problems and perspectives for its conservation

It is almost a miracle that T. Nakabo, K. Nakayama, N. Muto, and M. Miyazawa (2011) have discovered an extant population of Oncorhynchus kawamurae, or Kunimasu as the standard Japanese name, from Lake Saiko, Yamanashi Prefecture, Japan, from outside of its original distribution. Kunimasu had been believed to be extinct for more than 70 years in the type locality (and only known locality), Lake Tazawa, Akita Prefecture, owing to the introduction of strongly acidic water to the lake. This great discovery is certainly epoch-making in the study of the conservation of threatened freshwater fishes in Japan. The extant population seems to be safe so far under the conditions of local fishery activity in Lake Saiko. Nakabo et al. (2011) basically succeeded in clarifying both the morphological distinction and genetic isolation of Kunimasu from those of another sympatrically occurring kokanee, Oncorhynchus nerka, or Himemasu, which was also introduced to Lake Saiko from Hokkaido before World War II. Those facts consequently confirm the specific (not subspecific) status (sensu Mayr 1942, 1969) of Kunimasu as O. kawamurae, referring to some ecological peculiarity, i.e., deep swimming/spawning layer and spawning in winter or spring. However, its basic biology remains too obscure, so the information to certify them as O. kawamurae and subsequent protection for this valuable extant population is not yet sufficient. Major problems are as follows. (1) Genetic property: The small number of the specimens examined (n = 9) is not sufficient to show their full population genetic traits. Nakabo et al. (2011) successfully rejected large-scale hybridization between Kunimasu and Himemasu in Lake Saiko. The presumed differences in spawning season and sites may have worked as reproductive isolation mechanisms. However, their data cannot rule out the possibility that they have partially hybridized and some gene introgression from Himemasu to Kunimasu (and vice versa) has occurred. A huge number of Himemasu had already been introduced even to Lake Tazawa for a period of 30 years (Sugiyama 2000). Only morphologically typical specimens might have been examined by Nakabo et al. (2011). Information on the founder effect during the introduction process is lacking for both Kunimasu and Himemasu in Lake Saiko. Taking into consideration the repeated artificial transplantation of Himemasu among several lakes, the original geographic variation of Himemasu should be clarified, and the Kunimasu population in Lake Saiko should be compared with it by using adequate molecular markers. Verifiable information on the presence/ absence or extent of gene introgression is essential when reintroduction or conservation/benign introduction of this ‘‘extinct in the wild’’ species is considered. It has not been concluded yet whether the Kunimasu population in Lake Saiko is genetically pure. Genetic comparison between the current and original Kunimasu specimens would be the only direct test to certify the ‘‘rediscovery.’’ DNA analysis for old formalin-fixed specimens is generally difficult or impossible (Sugiyama 2000). However, recently developed next-generation sequencers might have the power to pick up and sequence short DNA fragments even from such old specimens. K. Hosoya Nature Conservation Committee of the Ichthyological Society of Japan, Tokyo, Japan