Food Habits of Narrow-Ridged Finless Porpoises Neophocaena asiaeorientalis sunameri in Ise and Mikawa Bays, Central Japan Revealed through Stomach Content Analysis

A stomach content analysis of 80 stranded and bycatch narrow-ridged finless porpoises in Ise and Mikawa Bays, central Japan, was conducted between 1992 and 2020. Prey items were identified in 76 samples. We combined three types of analyses to comprehensively explain their feeding habits: 1) numerical abundance and frequency of occurrence were used to analyze prey type utilization, 2) a combined rank index was used to search for important prey taxa, and 3) cluster analysis of flexible mixture modeling was used to detect the characteristics of feeding. Our results showed that the food habits of this population were characterized by frequent cephalopod and nektonic fish feeding and infrequent but large amount of benthic fish feeding. They changed their prey seasonally, where cephalopods were dominant during the spring-summer season. Cephalopods belonging to Teuthida and Octopoda, and fish belonging to Clupeiformes, Sillagidae, Gobiidae, and Callionymiae were suggested as important prey. We showed that in Ise and Mikawa Bays, porpoises likely feed opportunistically on various fish species and cephalopods.