ESR 16:149-163 (2012)  -  DOI:

Age estimation, growth and age-related mortality of Mediterranean monk seals Monachus monachus

Sinéad Murphy1,*, Trevor R. Spradlin1,2, Beth Mackey1, Jill McVee3, Evgenia Androukaki4, Eleni Tounta4, Alexandros A. Karamanlidis4, Panagiotis Dendrinos4, Emily Joseph4, Christina Lockyer5, Jason Matthiopoulos1

1Sea Mammal Research Unit, Scottish Oceans Institute, University of St. Andrews, St. Andrews, Fife KY16 8LB, UK
2NOAA Fisheries Service/Office of Protected Resources, Marine Mammal Health and Stranding Response Program, 1315 East-West Highway, Silver Spring, Maryland 20910, USA
3Histology Department, Bute Medical School, University of St. Andrews, St. Andrews, Fife KY16 9TS, UK
4MOm/Hellenic Society for the Study and Protection of the Monk Seal, 18 Solomou Street, 106 82 Athens, Greece
5Age Dynamics, Huldbergs Allé 42, Kongens Lyngby, 2800, Denmark

ABSTRACT: Mediterranean monk seals Monachus monachus are classified as Critically Endangered on the IUCN Red List, with <600 individuals split into 3 isolated sub-populations, the largest in the eastern Mediterranean Sea. Canine teeth collected during the last 2 decades from 45 dead monk seals inhabiting Greek waters were processed for age estimation. Ages were best estimated by counting growth layer groups (GLGs) in the cementum adjacent to the root tip using unprocessed longitudinal or transverse sections (360 µm thickness) observed under polarized light. Decalcified and stained thin sections (8 to 23 µm) of both cementum and dentine were inferior to unprocessed sections. From analysing patterns of deposition in the cementum of known age-maturity class individuals, one GLG was found to be deposited annually in M. monachus. Ages ranged from 0.5 to 36 yr for females, 0.5 to 21 yr for males and 0.5 to 25.5 yr for individuals of unknown sex. The majority of seals (65%) were considered adults (≥4 yr), followed by juveniles (20%, <1 yr) and sub-adults (15%, 1−3.9 yr). Thirty percent of the aged sample had died from human-related causes, such as accidental entanglement in fishing gear and direct killings. A single-Gompertz growth curve was generated for both sexes using standard length data, resulting in asymptotic values of 212.3 cm for females and 221.8 cm for males. This study represents the first quantitative glimpse of sex-specific growth in monk seals and the age structure of dead individuals in this rare species’ core range.

KEY WORDS: Mediterranean monk seal · Monachus monachus · Teeth · Age estimation · Growth layer groups · Mortality · Endangered species · Conservation

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Cite this article as: Murphy S, Spradlin TR, Mackey B, McVee J and others (2012) Age estimation, growth and age-related mortality of Mediterranean monk seals Monachus monachus. Endang Species Res 16:149-163.

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