Examining an ontogenetic shift in the diet of the whitespotted bamboo shark Chiloscyllium plagiosum in northern Taiwanese waters

Abstract

The diet and feeding habits of the whitespotted bamboo shark (Chiloscyllium plagiosum) were described using stomach content analysis and stable isotope analysis based on 327 and 78 specimens, respectively, that were collected in northern Taiwanese waters from October 2013 to March 2015. The index of relative importance indicated that both females and males mainly fed on Demospongiae, unidentified organisms, Annelida, and crustaceans. Juveniles (< 65 cm in total length, TL) preferred Annelida and crustaceans, while adults (> 65 cm in TL) fed more on teleost fishes. Similar standardized diet breadths (Ba) were found for sharks caught by different fishing gear and for sharks at different maturity stages; however, seasonal variation in Ba was noted. These results suggest that the whitespotted bamboo shark is a prey specialist. No significant differences in prey composition among fishing gear, sexes, maturity stages, or seasons were found by the multi-variate statistical analysis. Permutational multi-variate analysis of variance and a global test also indicated that there were no significant differences in diets between the maturity stages and sexes. The stable isotope analysis indicated that the mean values of δ15N and δ13C for the females and males were similar, suggesting the existence of high overlap in terms of feeding for both sexes. A multi-variate analysis of variance indicated that significant differences were found for the mean values of δ13C and δ15N among the different seasons, maturity stages and season–maturity stage interactions. These results suggested that an ontogenetic shift in the diet of C. plagiosum may occur when the fish approach the size of maturity.