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).

Carbon and nitrogen stable isotope ratios (i.e., δ13 C and δ15 N 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 δ13 C and δ15 N 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 δ13 C and δ15 N 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 δ13 C and δ15 N 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.

Sound variation and function in captive Commerson's dolphins (Cephalorhynchus commersonii).

Commerson's dolphin (Cephalorhynchus commersonii), one of the smallest dolphin species, has been reported to produce only narrow-band high-frequency (NBHF) clicks and no whistles. To clarify their sound repertoire and examine the function of each type, we analysed the sounds and behaviour of captive Commerson's dolphins in Toba Aquarium, Japan. All recorded sounds were NBHF clicks with peak frequency >110kHz. The recorded click-trains were categorised into four types based on the changing pattern of their Inter-click intervals (ICI): Decreasing type, with continuously decreasing ICI during the last part of the train; Increasing type, with continuously increasing ICI during the last part; Fluctuating type, with fluctuating ICI; and Burst-pulse type, with very short and constant ICI. The frequency of the Decreasing type increased when approaching an object newly introduced to the tank, suggesting that the sound is used for echolocation on approach. The Burst-pulse type suddenly increased in front of the object and was often oriented towards it, suggesting that it was used for echolocation in close proximity to the object. In contrast, the Increasing type was rarely recorded during approach, but increased when a dolphin approached another dolphin. The Increasing and Burst-pulse types also increased when dolphins began social behaviours. These results suggest that some NBHF clicks have functions other than echolocation, such as communication.

Hematology and serum biochemistry values in five captive finless porpoises (Neophocaena phocaenoides).

Hematological and serum biochemical values in five captive finless porpoises (Neophocaena phocaenoides) were examined, and abnormalities of aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase and γ-glutamyltransferase were determined in a male finless porpoise. The numbers of white and red blood cells in pregnant female porpoises were significantly lower than those in nonpregnant ones (P<0.05). Significantly higher values of serum creatinine were observed in summer when compared with the values in winter (P<0.01). Abnormalities of hepatic enzymes could improve with administration of ursodeoxycholic acid and a hepatic hydrolysate drug.