Volume 34, Issue 18 e8857
RESEARCH ARTICLE

Development of an analytical method to exclude the effect of decomposition on carbon and nitrogen stable isotope ratios using muscle samples collected from stranded narrow-ridged finless porpoise (Neophocaena asiaeorientalis)

Ayuma Furuyama

Ayuma Furuyama

Graduate School of Bioresources, Mie University, Tsu, Mie, 514-8507 Japan

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Taiga Yodo

Taiga Yodo

Graduate School of Bioresources, Mie University, Tsu, Mie, 514-8507 Japan

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Noriko Funasaka

Noriko Funasaka

Graduate School of Bioresources, Mie University, Tsu, Mie, 514-8507 Japan

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Ikuo Wakabayashi

Ikuo Wakabayashi

Toba Aquarium, Toba, Mie, 517-8517 Japan

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Tatsuya Oike

Tatsuya Oike

Minamichita Beachland Aquarium, Mihama, Aichi, 470-3233 Japan

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Motoi Yoshioka

Corresponding Author

Motoi Yoshioka

Graduate School of Bioresources, Mie University, Tsu, Mie, 514-8507 Japan

Correspondence

M. Yoshioka, Graduate School of Bioresources, Mie University, Tsu, Mie, 514-8507, Japan.

Email: [email protected]

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First published: 12 June 2020
Citations: 2

Peer Review: The peer review history for this article is available at https://publons.com/publon/10.1002/rcm.8857.

Rationale

Carbon and nitrogen stable isotope ratios (i.e., δ13C and δ15N values) in soft tissues of cetaceans are reported to change on decomposition. Care should be taken when determining the values using samples collected from dead-stranded cetaceans. We have developed a new analytical method to exclude the effect of decomposition on δ13C and δ15N values using muscles from narrow-ridged finless porpoises (Neophocaena asiaeorientalis).

Methods

The muscles from 53 fresh (bycatch and live-stranded individuals) and 213 dead-stranded individuals were analyzed by isotope ratio mass spectrometry combined with an elemental analyzer. The carbon and nitrogen content was compared between fresh and dead-stranded samples to investigate any decrease in the content with decomposition. In dead-stranded samples, the effect of changes in the carbon and nitrogen content and the C:N ratio (carbon/nitrogen) on δ13C and δ15N values was predicted by the generalized additive model (GAM).

Results

The carbon and nitrogen content (mean ± SE) in the muscles of fresh samples was 0.462 ± 0.0019 mg/mg and 0.147 ± 0.0005 mg/mg, respectively, while the content of dead-stranded samples was lower: carbon: 0.441 ± 0.0033 mg/mg and nitrogen: 0.135 ± 0.0012 mg/mg. When using the GAM, knowledge of the carbon and nitrogen content and the C:N ratio improved the prediction precision.

Conclusions

Prediction by the GAM showed changes in δ13C and δ15N values with a change in carbon and nitrogen content. The effect of decomposition can be excluded in statistical analysis of stranded samples by using samples with carbon and nitrogen content and C:N ratio equivalent to those of fresh samples or by using the carbon and nitrogen content and C:N ratio as an explanatory variable in the GAM.