著者

神田 育子 古山 歩 若林 郁夫 若井 嘉人 船坂 徳子 吉岡 基 Kanda Ikuko Furuyama Ayumi Wakabayashi Ikuo Wakai Yoshito Funasaka Noriko Yoshioka Motoi

出版者

三重大学大学院生物資源学研究科

雑誌

三重大学大学院生物資源学研究科紀要 = The bulletin of the Graduate School of Bioresources Mie University

巻号頁・発行日

vol.47, pp.13-23, 2021-12

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In this study, we aimed at clarifying the recent trends in narrow-ridged finless porpoise stranding on the west coast of Ise Bay. We analyzed the annual/monthly change in the number of stranded individuals, the status found, the length and sex of the individuals, and the seasonality of the geographical distribution data from 486 individuals collected along the northern central coast of Mie Prefecture for 10 years from January 2011 to December 2020. The annual number of stranded individuals fluctuated between 2011 and 2015, although it was stably around 60 individuals after 2016 when a local stranding network of universities, aquariums, museums, and local governments were established. As for the status of stranding, 96.5% of the individuals were found alone and they were dead except one. More males were observed among the stranded individuals than females with a sex ratio of 1.4. The body length frequency data showed that 75-85 cm individuals, approximately of birth length, accounted for 51.1% and 39.1% in the male and female groups, respectively, and stranding during the newborn period was overwhelmingly predominant. Several individuals below the birth length were found in April-July while the peak of calving season was considered to be April-June. The monthly number of stranded individuals peaked in May-June every year, and dead newborn calves were major factors in boosting the number of stranded individuals found during this period. The geographical distribution of stranded individuals displayed seasonal changes. Most stranded animals were recorded in the central part of the west coast of Ise Bay in April-June, exhibiting a gradual decrease and becoming scarce by January-March.