Quantification of the rate of stingray predation on short-neck clams(Ruditapes philippinarum)on the Midorikawa River tidal flat in Ariake Bay, Kyushu, Japan

Abstract

Stingrays, including longheaded eagle ray(Aetobatus flagellum),have been the target of eradication activities as they are considered to prey on short-neck clams(Ruditapes philippinarum).However, stingrays play a critical role as a keystone species in tidal flat communities. To date, the assessment of stingray predation on short-neck clams has only been limited to laboratory experiments and gut content analyses. Therefore, to conserve both stingrays and short-neck clams, it is necessary to quantitatively evaluate the stingray predation on short-neck clams. In this study, we focused on the foraging pits made by stingrays on the Midorikawa River tidal flat in Ariake Bay, Kyushu, Japan. Moreover, we estimated the rate of stingray predation on short-neck clams and examined the magnitude of the effects of predation on the decline of short-neck clams using unmanned aerial vehicle and quantitative surveys. We found that the maximum rate of stingray predation on short-neck clams was 0.29% per day, which accounted for approximately 17.7% of the overall mortality rate of short-neck clams during the same month. Therefore, our findings suggest that stingray predation exerts only a limited effect on the decline of short-neck clam stocks in the study area.