Impact of duck predation on the population of Manila clam (Ruditapes philippinarum) in tidal flat

Abstract

Ducks such as mallards (Anas platyrhynchos), have been the target of predation control, including extermination efforts, on land and in coastal regions, because they fly in colonies and prey on a wide variety of agricultural crops and marine products, including Manila clams (Ruditapes philippinarum). To date, stomach content analysis and behavioral observations have primarily been used to assess duck predation on clams. Although ducks appear to respond to water depth, their response to short-term changes in water depth (i.e., tidal height) has not been assessed in tidal flats. Therefore, a quantitative evaluation of the effects of duck predation on clams is needed to clarify the behavior of ducks on tidal flats and to conserve ducks and clams. In this study, the influence of duck predation on the clam population was investigated using anti-predation experiments on the Midorikawa River tidal flat in Ariake Bay, Kyushu, Japan. Furthermore, the relationships among water depth, duck activity, and duck flock density were investigated using a trail camera and a drone. In the anti-predation experiment during the study period, no significant difference in clam density was found between the experimental and control clam density. This study showed that duck predation may have a small impact on the Manila clam population in the tidal flats of the Midorikawa River.