Resumen
The changes in the stable isotope ratios of carbon (d13C), nitrogen (d15N), oxygen (d18O), and mercury (Hg) concentrations in muscle and liver tissues during and after lactation were studied in killer whales stranded along the coast of Hokkaido, in the northern area of Japan (n = 16). Calf muscles displayed d13C- and d15N-enriched peaks and a d18O-depleted peak during lactation. The d13C- and d15N-enriched peaks appear to reflect the extensive nursing of 13C- and 15N-enriched milk and the onset of weaning, whereas the d18O-depleted peak may be attributable to the extensive nursing of 18O-depleted milk and the onset of weaning. The d13C and d15N values tended to gradually increase after the weaning, whereas the d18O values tended to decrease. The d13C and d15N levels in calves were similar between liver and muscle samples, whereas those in mature animals were higher in liver than in muscle samples. The isotopic turnover rates of C and N may be similar between the liver and muscle tissues in calves, which are rapidly growing animals. The Hg concentrations in muscle tissues were slightly higher in small calves than in large calves, probably due to the Hg transfer across placenta. The Hg concentrations in liver and muscle samples increased with increasing body length, and those in two liver samples from mature animals exceeded the high-risk threshold for marine mammal health effects (82 µg/wet g).