Influences of human maintenance work for ditch on nesting habitat of ninespine stickleback, Pungitius pungitius

We studied that maintenance work on the irrigation ditches in Akita Prefecture had effect on the nest building conditions of Pungitius pungitius and examined methods for the conservation of their nesting habitats. As a result of the action of maintenance work once between May and August compared with a single maintenance work done at the beginning of May, the number of nests decreased from 36 to 14. When frequent maintenance was carried out, the water level fell, the water velocity got faster at nest sites and the number of aquatic plants that were capable of supporting nests decreased. For the conservation of the nest-building environment, management of maintenance activities in areas other than those that the ninespine stickleback, Pungitius pungitius use for nesting and management of the plants that need to be eliminated is essential. As for methods of conservation nesting habitats and improvement ability of flow, we proposed maintenance work with conservation area. The conservation area is a 50-60 m section of curved area where Sparganium japonicum communities grow and a 50-72 m section of the right bank where Acorus gramineus communities grow.