[A-CG39] Coastal Ecosystems - 1. Water Cycle and Land-Ocean Interactions

[ACG39-10] Influence of ducks on the short-neck clam population in tidal flats: a study of duck response to water depth

*Rikuto Honda¹, Tomohiro Komorita¹, Tatsuya Ozaki¹, Nana Yamashita¹, Takehisa Yamakita² (1.Prefectural University of Kumamoto, 2.JAMSTEC)

Keywords:Ariake Bay, migration bird, Ruditapes philippinarum, tidal flat

Ducks, including mallards (Anas platyrhynchos), have been the target of eradication efforts because they are thought to predate short-neck clams (Ruditapes philippinarum). However, ducks are an important component of coastal ecosystems. To date, stomach content and behavioral observations have been primarily used to assess duck predation on clams. Although ducks are active in response to water depth, short-term tidally induced migration ecology has not been assessed on tidal flats. Therefore, quantitatively evaluating the effects of ducks on clams is necessary to clarify the behavior of ducks on tidal flats and to conserve ducks and clams. In this study, the effects of ducks on clams were investigated using antipredation experiments on the Midorikawa tidal flat in Ariake Bay, Kyushu, Japan. Furthermore, the relationship among water depth, duck activity, and duck density was investigated using a fixed-point camera and a drone. Results showed that ducks predate on only about 3% of individuals per unit area during the 5 months they fly to this tidal flat based on the results of the fixed-point camera and drone monitoring. In the experiment for preventing predation during the study period, no significant difference in the number of clams was found between “without protection” and “under protection”. In this study, the impact of duck predation on clams was not significant.