Reproduction of Kunimasu, Oncorhynchus kawamurae (Salmonidae), in Lake Saiko, Yamanashi Prefecture, Japan II. Spawning and inhibiting factors

Abstract

Kunimasu, Oncorhynchus kawamurae, spawning and its inhibiting factors were investigated in Lake Saiko, central Japan, by direct observation while scuba diving and recording images using underwater time-lapse cameras. The cameras were installed on three stations in gravel areas with high or low spring water discharge at a depth of c.a. 30 m from November 2016 to February 2017. Kunimasu were observed to visit these areas, and digging behavior was observed. It was inferred that the number of fish visiting the gravel areas was related to the size of the gravel areas rather than the magnitude of spring water discharge. The underwater cameras confirmed the presence of freshwater eels, which were actively digging gravel and eating Kunimasu eggs. Two eels captured were identified to be European eel, Anguilla anguilla, by mitochondrial DNA sequence analysis. Since we found only a few Kunimasu eggs on the spawning ground, the egg-eaters appear to have had a substantial negative impact on the reproduction of Kunimasu. These results indicate that the maintenance of gravel areas and spring water, as well as the expulsion of the European eel, are vital for the conservation of the Kunimasu population in Lake Saiko.