Survey of the Lotus Root Habitats in the Sediment Using Acoustic Coring System

The lotus plant (Nelumbo nucifera Gaertn.) is an aquatic emergent angiosperm that is distributed in wetlands. In Japan, the lotus is widely distributed in Japanese eutrophic waters [1]. A large proportion of Lake Izunuma has been dominated by lotus, and the area of the lake covered by lotus has increased. The lake was registered as a wetland under the Ramsar Convention in 1985, and therefore, there is a great need to conserve the biodiversity at the lake. Lake Izunuma-Uchinuma is also designated as a National Bird and Animal Protection Region, and it is one of the most famous wintering grounds for whooper swans and geese in Japan [2]. Additionally, foraging behavior of whooper swans was observed often at the survey areas. Therefore, the lotus root is important food for the whooper swans during overwinter and the lotus distribution in the lake affects their behavior [3]. However, the lotus plant usually grows by vegetative reproduction of the lotus root under the water bottom, and the real situation of the lotus distribution is not clear unless the lotus root is dug up. To overcome the problems, we have developed a new monitoring system, named “acoustic coring system” [4]. In this study, the lotus root habitats in the sediment is monitored using the acoustic coring system to investigate the lotus root distribution and estimate the foraging pressure of whooper swan during overwinter.