Stable isotopes confirm a coastal diet for critically endangered Mediterranean monk seals

^†Contribution to the Special Issue “Stable Isotopes in Mammals”.

Abstract

Understanding the ecology and behaviour of endangered species is essential for developing effective management and conservation strategies. We used stable isotope analysis to investigate the foraging behaviour of critically endangered Mediterranean monk seals (Monachus monachus) in Greece. We measured carbon and nitrogen isotope ratios (expressed as δ¹³C and δ¹⁵N values, respectively) derived from the hair of deceased adult and juvenile seals and the muscle of their known prey to quantify their diets. We tested the hypothesis that monk seals primarily foraged for prey that occupy coastal habitats in Greece. We compared isotope values from seal hair to their coastal and pelagic prey (after correcting all prey for isotopic discrimination) and used these isotopic data and a stable isotope mixing model to estimate the proportion of coastal and pelagic resources consumed by seals. As predicted, we found that seals had similar δ¹³C values as many coastal prey species and higher δ¹³C values than pelagic species; these results, in conjunction with mean dietary estimates (coastal=61 % vs. pelagic=39 %), suggest that seals have a diverse diet comprising prey from multiple trophic levels that primarily occupy the coast. Marine resource managers should consider using the results from this study to inform the future management of coastal habitats in Greece to protect Mediterranean monk seals.

Keywords:

• carbon-13
• diet
• endangered species
• food web
• foraging
• Greece
• isotope ecology
• Monachus monachus
• nitrogen-15
• seals

Acknowledgements

We would like to thank the Hellenic Centre for Marine Research for providing potential prey samples. This study was conducted in accordance with the guidelines of the research permits (92705/770/09-03-05 and 86286/340/31-01-07) issued by the Hellenic Ministry of Rural Development and Food. The data of the study were partially collected within the framework of the LIFE Nature project ‘Monk seal and fisheries: Mitigating the conflict in Greek seas’ (LIFE05NAT/GR/000083). We thank G. Strauch and two anonymous reviewers for critical comments on an earlier draft of the manuscript.

Notes

^† Contribution to the Special Issue “Stable Isotopes in Mammals”.