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摘要
We investigated the dietary habits of the polkadot skate, Dipturus chinensis (Japanese name: Gangi-ei), in the East China Sea by analyzing the stomach contents of 529 individuals. Of these, 18 (3.40%) had empty stomachs. The mean and maximum fullness indices (FIs) were 0.67% and 6.12%, respectively. The mean FI of female skates > 500 mm in total length (TL) was higher than that of males and smaller females. The most dominant prey category was crustaceans, which included shrimps, crabs, and anomurans, followed by fishes. Cephalopods were additionally observed. Dipturus chinensis fed on a wide variety of crustacean taxa, and among them, Caridea and Galatheidae were particularly common. Fishes that could be identified were mostly demersal fishes, such as Callionymidae, Triglidae, and Rajidae. Some juvenile D. chinensis were also observed, indicating that cannibalism occurs in this species. Even though dental sexual dimorphism was observed in large size classes (mainly > 500 mm TL), the diet of males and females significantly overlapped. Size-related dietary shifts from small crustaceans, such as shrimps and anomurans, to relatively fast-swimming prey, such as fishes, crabs, and cephalopods, were observed in all seasons. The composition of these prey categories varied among seasons. Shannon-Wiener diversity indices calculated for each size class ranged from 2.01 to 2.51, indicating D. chinensis are generalist predators. As size increased, trophic level increased from 3.58 to 3.85, indicating that larger specimens are at a slightly higher trophic level than smaller specimens. These results suggest that D. chinensis are middle-trophic-level generalist predators that utilize diverse prey depending on their size and the season, and thus play an influential role in the demersal ecosystem of the East China Sea.
- 出版日期2018-7
