From the forests to teeth: Visual crossdating to refine age estimates in marine mammals

Hamilton, Vicki; Evans, Karen; Hindell, Mark A.

doi:10.1111/mms.12392

Cited by 3 publications

(2 citation statements)

References 21 publications

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“…Teeth GLGs have been used to assess climate–growth relationships in odontocetes (Dellabianca et al 2011; Hamilton et al 2017) and fur seals (Boyd and Roberts 1993; Hanson et al 2009; Knox et al 2014; Wittmann et al 2016). Earbone GLGs of manatees, whose health is closely associated with seagrass habitat and coastal water temperature, may also be influenced by extrinsic variables.…”

Section: Discussionmentioning

confidence: 99%

“…It is thought that the narrow adhesion line forms during periods of reduced growth (in most cases during winter or when there is reduced foraging, migration, hibernation, or environmental stressors), whereas the broader band forms during periods of rapid growth (when food resources are abundant or an animal is allocating more nutrients toward growth—Weinmann and Sicher 1947; Sissons 1949, 1971; Morris 1972; Klevezal 1996). The rate of GLG deposition can vary among species and individuals, as well as with environmental variables, sex, geographic region, life-history events, and various stressors (Scheffer and Peterson 1967; Harwood and Prime 1978; Klevezal and Myrick 1984; Manzanilla 1989; Boyd and Roberts 1993; Klevezal and Stewart 1994; Klevezal 1996; Hanson et al 2009; Medill et al 2010; Dellabianca et al 2011; Knox et al 2014; Wittmann et al 2016 and references therein; Hamilton et al 2017).…”

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confidence: 99%

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Accuracy, precision, and error in age estimation of Florida manatees using growth layer groups in earbones

Lonati

Howell

Hostetler

et al. 2019

Journal of Mammalogy

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Ages of Florida manatees (Trichechus manatus latirostris) can be estimated by counting annual growth layer groups (GLGs) in the periotic dome portion of the tympanoperiotic complex of their earbones. The Florida Fish and Wildlife Conservation Commission manages an archive of more than 8,700 Florida manatee earbones collected from salvaged carcasses from 1989 to 2017. Our goal was to comprehensively evaluate techniques used to estimate age, given this large sample size and changes to processing protocols and earbone readers over time. We developed new standards for estimating ages from earbones, involving two independent readers to obtain measurements of within- and between-reader precision. To quantify accuracy, precision, and error, 111 earbones from manatees with approximately known ages (first known as calves: “KAC”) and 69 earbones from manatees with minimum known ages (“MKA,” based on photo-identification sighting histories) were processed, and their ages were estimated. There was greater precision within readers (coefficient of variation, CV: 2.4–8.5%) than between readers (CV: 13.1–13.3%). The median of age estimates fell within the true age range for 63.1% of KAC cases and was at least the sighting duration for 75.0% of MKA cases. Age estimates were generally unbiased, as indicated by an average raw error ± SD of −0.05 ± 3.05 years for the KAC group. The absolute error (i.e., absolute value of raw error) of the KAC data set averaged 1.75 ± 2.50 years. Accuracy decreased and error increased with increasing known age, especially for animals over 15 years old, whose ages were mostly underestimated due to increasing levels of resorption (the process of bone turnover that obscures GLGs). Understanding the degree of uncertainty in age estimates will help us assess the utility of age data in manatee population models. We emphasize the importance of standardizing and routinely reviewing age estimation and processing protocols to ensure that age data remain consistent and reliable.

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