**3. Ontogenetic change in δ15N and δ13C signatures of marine mammals stranded in Hokkaido, Japan**

### **3.1 Stranding of marine mammals along the coast of Hokkaido, Japan**

Hokkaido is the northernmost island in Japan and is surrounded by the North Pacific Ocean, the Sea of Japan, and the Sea of Okhotsk. Most stranded cetaceans in Hokkaido are odontocetes, such as DP, harbor porpoise (*Phocoena phocoena*), Pacific white-sided dolphin (*Lagenorhynchus obliquidens*), and the mysticete MW. In this section, we describe the δ15N and δ13C profiles in muscle samples of MW and DP calves, in addition to the muscle samples of Kurill harbor seals (*Phoca vitulina stejnegeri*; HS) stranded in Hokkaido. Furthermore, we compared the δ15N and δ13C values in calf muscle samples from MW, DP and KW stranded in Hokkaido. We analyzed the δ15N and δ13C values in the muscle samples after lipid extraction.
