First Stranding Record of the Fraser’s Dolphin Lagenodelphis hosei in Kanagawa, Japan

Abstract

A debilitated female dolphin was stranded on Kugenuma-Kaigan, Kanagawa Prefecture, Japan (35° 18’ 55” N, 139° 27’ 57” E) on 13 August 2022. This individual was rescued and transported to the Yokohama Hakkeijima Sea Paradise, but unfortunately died the next day. We carried out morphological survey, dissection, blood analysis, and genomic analysis for the animal. The dolphin was 241.2 cm in body length and had a short (1.1 % of the body length) but distinct beak and proportionally small flippers. The mitochondrial control region sequence of the specimen showed the highest homology (99.06 %) with that of Fraser’s dolphin Lagenodelphis hosei. Based on these data, this individual was identified as a Fraser’s dolphin. Blood biochemical parameters indicated that the individual was under low-nutrition and dehydrated condition, and inflammation was occurred. To the best of our knowledge, this is the first stranding record of this species in Kanagawa Prefecture. The sea surface temperature off Kugenuma-Kaigan was over 25 ºC around on the stranding day, which corresponded to that of the primary distribution range of this species. Sea surface temperatures over 25 ºC are usually observed in Sagami Bay in summer, and this stranding event indicates the stranding/sighting of this species would occur again off Kanagawa when high sea surface temperatures and other environmental condition are satisfied. Age determination, osteological study, histological observation of the specimen, and accumulation of stranding/sighting information of this species are the next steps to understand the maturation and distribution pattern. The whole skeleton was cataloged in the Kanagawa Prefectural Museum of Natural History.