EFFECT OF SEASONAL CHANGES AND RIVER STRUCTURES ON THE BEHAVIORAL PATTERNS OF THE HYBRID GIANT SALAMANDER IN THE KAMO RIVER, JAPAN

The introduction of Chinese Giant Salamanders (Andrias davidianus) has been a problem in various regions in Japan. Hybridization between A. davidianus and native Japanese Giant Salamanders (A. japonicus) has jeopardized survival of the latter species. Conservation of A. japonicus requires implementation of measures that prevent further interbreeding. The lack of knowledge of the behavior of Andrias spp., however, impedes development of appropriate conservation strategies. We used biotelemetry to examine seasonal variations in behavioral patterns of seven hybrid giant salamanders in the Kamo River, Kyoto, Japan. We successfully tracked five individuals for one year. Hybrids occupied habitats within 50 m downstream of vertical river structures significantly more frequently during the pre-breeding (May-August) and post-breeding (September-December) seasons than during nonbreeding months (January-April; chi(2) = 124.7, df = 4, P < 0.001). Home range (Kernel Density Estimations; KDE) tended to be larger in September-December (95% KDE: 208.3 +/- 70.7 m; 50% KDE: 57.2 +/- 34.7 m) but smaller in January-April (95% KDE: 108.1 +/- 65.3 m; 50% KDE: 22.7 +/- 8.6 m). Water level and season had no significant effects on either distance or direction of movement. Movement was, however, affected by weirs installed to mitigate flooding affects; hybrids traveled upstream over only two of 11 of these structures. We propose leaving intact the river structures in the lower reach and conducting intensive captures at breeding sites and below the river structures during the breeding season to identify and remove introduced or hybrid individuals to limit potential hybridization.