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Robust age estimation of southern sea otters from multiple morphometrics.

Authors
  • Nicholson, Teri E1
  • Mayer, Karl A1
  • Staedler, Michelle M1
  • Gagné, Tyler O1
  • Murray, Michael J1
  • Young, Marissa A1
  • Tomoleoni, Joseph A2
  • Tinker, Martin Tim2, 3
  • Van Houtan, Kyle S1, 4
  • 1 Monterey Bay Aquarium Monterey CA USA.
  • 2 U.S. Geological Survey Western Ecological Research Center Santa Cruz CA USA.
  • 3 Department of Ecology and Evolutionary Biology Long Marine Laboratory University of California Santa Cruz CA USA.
  • 4 Nicholas School of the Environment Duke University Durham NC USA.
Type
Published Article
Journal
Ecology and Evolution
Publisher
Wiley (John Wiley & Sons)
Publication Date
Aug 01, 2020
Volume
10
Issue
16
Pages
8592–8609
Identifiers
DOI: 10.1002/ece3.6493
PMID: 32884643
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

Reliable age estimation is an essential tool to assess the status of wildlife populations and inform successful management. Aging methods, however, are often limited by too few data, skewed demographic representation, and by single or uncertain morphometric relationships. In this study, we synthesize age estimates in southern sea otters Enhydra lutris nereis from 761 individuals across 34 years of study, using multiple noninvasive techniques and capturing all life stages from 0 to 17 years of age. From wild, stranded, and captive individuals, we describe tooth eruptions, tooth wear, body length, nose scarring, and pelage coloration across ontogeny and fit sex-based growth functions to the data. Dental eruption schedules provided reliable and identifiable metrics spanning 0.3-9 months. Tooth wear was the most reliable predictor of age of individuals aged 1-15 years, which when combined with total length, explained >93% of observed age. Beyond age estimation, dental attrition also indicated the maximum lifespan of adult teeth is 13‒17 years, corresponding with previous estimates of life expectancy. Von Bertalanffy growth function model simulations of length at age gave consistent estimates of asymptotic lengths (male Loo = 126.0‒126.8 cm, female Loo = 115.3‒115.7 cm), biologically realistic gestation periods (t 0 = 115 days, SD = 10.2), and somatic growth (male k = 1.8, SD = 0.1; female k = 2.1, SD = 0.1). Though exploratory, we describe how field radiographic imaging of epiphyseal plate development or fusions may improve aging of immature sea otters. Together, our results highlight the value of integrating information from multiple and diverse datasets to help resolve conservation problems. © 2020 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.

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