Ontogenetic Growth Changes in Mercury and Stable Isotope Ratios of Carbon, Nitrogen, and Oxygen in Male and Female <i>Dalli</i>-Type Dall’s Porpoises (<i>Phocoenoides dalli</i>) Stranded in Hokkaido, Japan

Ontogenetic Growth Changes in Mercury and Stable Isotope Ratios of Carbon, Nitrogen, and Oxygen in Male and Female <i>Dalli</i>-Type Dall’s Porpoises (<i>Phocoenoides dalli</i>) Stranded in Hokkaido, Japan

We investigated the ontogenetic growth changes in total mercury (THg) concentrations, δ<sup>13</sup>C, δ<sup>15</sup>N, and δ<sup>18</sup>O values, and body length (BL) of <i>dalli</i>-type Dall’s porpoises. THg concentrations in the liver of mature po...

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Bibliographic Details
Main Authors:	Tetsuya Endo, Osamu Kimura, Masaru Terasaki, Yoshihisa Kato, Yukiko Fujii, Koichi Haraguchi
Format:	Article
Language:	English
Published:	MDPI AG 2025-04-01
Series:	Journal of Marine Science and Engineering
Subjects:	lactation mercury stable isotope ratio of carbon stable isotope ratio of nitrogen stable isotope ratio of oxygen Dall’s porpoise (<i>Phocoenoides dalli</i>)
Online Access:	https://www.mdpi.com/2077-1312/13/5/892
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Summary:	We investigated the ontogenetic growth changes in total mercury (THg) concentrations, δ<sup>13</sup>C, δ<sup>15</sup>N, and δ<sup>18</sup>O values, and body length (BL) of <i>dalli</i>-type Dall’s porpoises. THg concentrations in the liver of mature porpoises stranded in Hokkaido, Japan, were markedly higher than those in the muscle. The THg concentrations in the livers of males and females increased sharply when their BLs exceeded approximately 1.9 m and 1.8 m, respectively, the BLs at which they might attain maturity. The asymptotes of the THg increases were close to their maximum BLs of 2.2 m and 2.0 m for males and females, respectively. The δ<sup>15</sup>N levels in muscles were higher in the calves than in the weaned porpoises, probably due to the consumption of <sup>15</sup>N-enriched milk, whereas the δ<sup>13</sup>C values in the calves were variable and similar to those in the weaned porpoises. The δ<sup>18</sup>O values of male and female muscles increased with increasing BL. Positive correlations were found between the THg concentrations and either the δ<sup>13</sup>C values or the δ<sup>18</sup>O values in the weaned animals, but not with the δ<sup>15</sup>N values. These results imply a feeding shift towards deeper pelagic areas with growth, as the δ<sup>13</sup>C and δ<sup>18</sup>O values and the THg concentrations tend to be higher in these areas.
ISSN:	2077-1312