Distribution and habitat characterisation of unionid mussels in irrigation ditches in Kinomoto-cho,Nagahama City, Shiga Prefecture

Abstract

A field survey was conducted in irrigation ditches in Kinomoto-cho, Nagahama City, Shiga Prefecture to clarify the distribution and habitat characteristics of unionid mussels. Seven unionid species (Pronodularia japanensis, Pseudodon omiensis, Sinanodonta japonica, Lanceolaria grayana, Inversidens brandtii, Nodularia douglasiae biwae and Inversiunio yanagawensis) were collected from October to November 2015. The relationship between mussel density and physical factors was analysed using generalized linear models (GLMs) for all but one rare species (I. yanagawensis). The GLM results indicated that the densities of P. japanensis and P. omiensis were higher in ditches with a sand bottom, hard sediment and shallow depth; the density of S. japonica was higher in ditches with a sand bottom, hard sediment, shallow depth and slow flow velocity; the density of L. grayana was higher in ditches with a sand bottom and hard sediment, and the density of N. d. biwae was higher in ditches with hard sediment and slow flow velocity. No parameter clearly affected the density of I. brandtii. A range of ditch environments should be maintained or restored to conserve unionid mussels because mussel species are likely to differ in terms of the most suitable environment for habitation.