Food Habits of Narrow-Ridged Finless Porpoises (Neophocaena asiaeorientalis) in Sendai Bay–Tokyo Bay, Japan

Stomach contents of 23 narrow-ridged finless porpoises (Neophocaena asiaeorientalis) from Sendai Bay–Tokyo Bay, Japan, were examined. These specimens had been stranded and were collected in 1996–2016. Of the 23 stomachs, 19 contained hard parts of prey, and 421 prey items were retrieved from all stomachs. We assessed the importance of prey species using the percentage of numerical abundance of the prey species (%N) and the frequency of occurrence of the prey species (%F), which were as follows: cephalopods, 78.9 %N; fishes, 20.2 %F. Although different prey types, nekton, nektobenthos, and benthos, were present in stomachs, benthic species (families Octopodidae, Sepiolidae, and Sciaenidae) were frequently present. Families Loliginidae and Ommastrephidae, which exhibit diel vertical migrations and remain in the middle and/or bottom layers during the daytime, were also highly abundant. Evidently, narrow-ridged finless porpoises in Sendai Bay–Tokyo Bay most often prey on the bottom layer during the daytime and sometimes prey on species swimming in the surface layer.