Carbon, nitrogen, and oxygen stable isotope ratios of striped dolphins and short-finned pilot whales stranded in Hokkaido, northern Japan, compared with those of other cetaceans stranded and hunted in Japan

Abstract

Strandings of striped dolphins (SD) and short-finned pilot whales (PW) in Hokkaido, northern Japan, are rare but have recently increased, probably due to global warming. We quantified δ¹³C, δ¹⁵N, and δ¹⁸O in muscles of SD (n = 7) and PW (n = 3) stranded in Hokkaido and compared these values with those in muscles (red meat products) of hunted SD and PW in three areas of central and southern Japan. δ¹⁸O in stranded SD, except for the calf, decreased with increasing body length (BL), whereas δ¹³C increased, with no BL-related changes in δ¹⁵N. The variability of δ¹⁸O (range of maximum and minimum) was larger in the stranded SD (7.5 ‰) than of the hunted SD in three areas (0.9, 1.9, and 1.4 ‰), whereas that of δ¹⁵N was smaller in the stranded SD than in the hunted SD. Similarly, the variability of δ¹⁸O was larger in the stranded PW in Hokkaido (3.3 ‰) than in the hunted PW in central Japan (1.4 ‰). The larger variability of δ¹⁸O and smaller variability of δ¹⁵N in stranded SD imply long-term sojourning in coastal waters and feeding on small amounts of limited prey species at low trophic levels before death.

Keywords: Carbon-13; isotope ecology; mercury; migration; nitrogen-15; oxygen-18; short-finned pilot whales (Globicephala macrorhynchus); stranding; striped dolphins (Stenella coeruleoalba).