Food variations and ontogenetic dietary shift of the starspotteddogfish Mustelus manazo at five locations in Japan and Taiwan

Abstract

Stomach contents were examined from 936 individuals of Mustelus manazo, collected by trawl at five locations: Aomori, Tokyo Bay, Maizuru and Shimonoseki in Japan, and one location off Taiwan. The vacuity index was relatively low (0-6.1%). Based on three indices (%W, %F, RI), the major dietary component was crustaceans at all locations. The most important prey category was crabs in Aomori, Shimonosei and Taiwan, mantis shrimps in Tokyo Bay, and shrimps in Maizuru. Fishes were a minor food category for M. manazo in most locations, except in Maizuru where fishes were second in importance in the diet. Dietary overlap revealed a medium degree of overlap between Tokyo Bay and Aomori, and between Tokyo Bay and Shimonoseki. The other locations showed a high degree of overlap with each other. Significant ontogenetic dietary shifts were found in Tokyo Bay, Maizuru and Taiwan, and prey diversity showed a trend being relatively low in larger size classes. The feeding habit of M. manazo was unique in Tokyo Bay, where crustaceans in the muddy substrata were taken in preference to the most abundant benthic prey item available, such as a southern rough shrimp, Trachypenaeus curvirostris. Mustelus manazo appears to use two feeding strategies based upon stomach contents. One, in Tokyo Bay, involved the digging up or removing of burrowing invertebrates from muddy substrata without crushing them. The other, at the other four locations, involved the crushing of prey on the substrata surface.