The red stingray
Dasyatis akajei is a predator that is increasing in abundance in estuarine and coastal ecosystems in Japan. It is presumed to predate on commercial clams, but this relationship has not been demonstrated in Japan. We focused on the relationship between red stingrays and commercial clams and studied the food habits of red stingrays in estuarine ecosystems of the Hii River with high and low salinity, the Lakes Nakaumi and Shinji, respectively. Red stingrays were caught by longlines, sting, and small set nets from 12 sites on the Hii River. Food materials in the gastrointestinal tract of red stingrays were classified into several items. Frequency of occurrence were determined for each food item. Appearance of clams in the gastrointestinal tract of red stingrays differed among with respect to the species. Frequencies of occurrence of
Ruditapes philippinarum and
Corbicula japonica were high. The weight of
R. philippinarum was higher than that of
C. japonica . Red stingrays tend to prey on clams found in high density in L. Nakaumi. However, C. japonica is not extensively preyed upon by red stingrays despite its high density in L. Shinji. The ark shell
Anadara kagoshimensis did not appear from the gastrointestinal tract of red stingray.
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