Temporal shift in the isotopic niche of female Antarctic fur seals from Bouvetøya

Abstract

The Antarctic fur seal (Arctocephalus gazella) is a key marine predator in the Southern Ocean, a region that has recently started to show changes as a result of global climate change. Here, carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope analyses on whole blood and plasma samples were used to examine the isotopic niche of lactating female Antarctic fur seals. Using recently developed Bayesian approaches to determine changes in isotopic niche, a significant increase in δ¹³C and δ¹⁵N was found between 1997 and 2015; this change occurred at an average rate of 0.067‰ (δ¹³C) and 0.072‰ (δ¹⁵N) per year over this period. This suggests that a marked isotopic niche shift has occurred over this period, which very likely corresponds to a shift in diet towards prey at a higher trophic level, such as fish (replacing krill). Although our sampling design prevented us from exploring a seasonal trend in a conclusive manner, our data suggest that concurrent increases in δ¹³C and δ¹⁵N might occur as the breeding season progresses. At a seasonal scale, an average decrease of −0.7‰ per month (95% confidence interval=[−0.9; −0.6]) in δ¹³C might have occurred, concurrently with an average increase of 1.1‰ per month in δ¹⁵N. The results of this study constitute the first isotopic assessment for female Antarctic fur seals from Bouvetøya and provide a baseline for the use of this predator species as a sentinel of the marine trophic system in one of the least studied areas within this species’ distributional range.

• Arctocephalus gazella
• krill
• predation
• Southern Ocean
• stable isotopes
• trophic relationships.

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Acknowledgements

This work was supported by the Norwegian Antarctic Research Expedition programme and the Norwegian Polar Institute. We thank all of the people who have helped with sample collection over the years. All capture and handling procedures were done in accordance with the requirements of the Norwegian Animal Research Authority. We thank Heidi Ahonen (Norwegian Polar Institute) for preparing the samples and Ricardo Álvarez and Susana Carrasco (LIE) for conducting the lipid extractions and the isotopic analyses.

Notes

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