Changes in Carbon, Nitrogen, and Oxygen Stable Isotope Ratios and Mercury Concentrations in Killer Whales ( Orcinus orca ) during and after Lactation

• Published in: Journal of Marine Science and Engineering
• Main Authors: Tetsuya Endo, Osamu Kimura, Masaru Terasaki, Yoshihisa Kato, Yukiko Fujii, Koichi Haraguchi
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2024
• Subjects: lactation; feeding ecology; stable isotope of carbon; stable isotope of nitrogen; stable isotope of oxygen; Naval architecture. Shipbuilding. Marine engineering; VM1-989; Oceanography; GC1-1581; Orca; Orcinus orca
• Online Access: https://doi.org/10.3390/jmse12040623; https://doaj.org/article/db46d19a69a64447a12b30cd67323ff7

The changes in the stable isotope ratios of carbon (δ 13 C), nitrogen (δ 15 N), oxygen (δ 18 O), 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 δ 13 C- and δ 15 N-enriched peaks and a δ 18 O-depleted peak during lactation. The δ 13 C- and δ 15 N-enriched peaks appear to reflect the extensive nursing of 13 C- and 15 N-enriched milk and the onset of weaning, whereas the δ 18 O-depleted peak may be attributable to the extensive nursing of 18 O-depleted milk and the onset of weaning. The δ 13 C and δ 15 N values tended to gradually increase after the weaning, whereas the δ 18 O values tended to decrease. The δ 13 C and δ 15 N 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).