Age determination of common bottlenose dolphins (Tursiops truncatus) using dental radiography pulp:tooth area ratio measurements

Abstract

Age is an important parameter to better understand wildlife populations, and is especially relevant for interpreting data for fecundity, health, and survival assessments. Estimating ages for marine mammals presents a particular challenge due to the environment they inhabit: accessibility is limited and, when temporarily restrained for assessment, the window of opportunity for data collection is relatively short. For wild dolphins, researchers have described a variety of age-determination techniques, but the gold-standard relies upon photo-identification to establish individual observational life histories from birth. However, there are few populations with such long-term data sets, therefore alternative techniques for age estimation are required for individual animals without a known birth period. While there are a variety of methods to estimate ages, each involves some combination of drawbacks, including a lack of precision across all ages, weeks-to-months of analysis time, logistical concerns for field applications, and/or novel techniques still in early development and validation. Here, we describe a non-invasive field technique to determine the age of small cetaceans using periapical dental radiography and subsequent measurement of pulp:tooth area ratios. The technique has been successfully applied for bottlenose dolphins briefly restrained during capture-release heath assessments in various locations in the Gulf of Mexico. Based on our comparisons of dental radiography data to life history ages, the pulp:tooth area ratio method can reliably provide same-day estimates for ages of dolphins up to about 10 years old.

Multi-Tissue Methylation Clocks for Age and Sex Estimation in the Common Bottlenose Dolphin

“…Recent efforts to develop rapid, non-invasive methods for age determination include pectoral flipper bone ossification and dental radiographic determination of the pulp to tooth area ratio (Barratclough et al, 2019;Herrman et al, 2020). Although bone ossification and pulp to tooth ratios benefit from portability of radiography units that can be used in the field to estimate age within hours of image collection, they still require animal restraint and suffer from reduced accuracy with animals that have reached physical maturity (Barratclough et al, 2019;Herrman et al, 2020). By contrast, the epigenetic clocks described herein can accurately be applied to the entire life-span of the bottlenose dolphin.…”

“…As such, other aging methods have been evaluated for use with bottlenose dolphins or other cetaceans including eye lens aspartic acid racemization (Bada et al, 1980;George et al, 1999), fatty acid composition (Koopman et al, 1996;Herman et al, 2009;Marcoux et al, 2015), radiocarbon 14 dating from fallout (Stewart et al, 2006), telomere length (Olsen et al, 2012), radiograph changes in tooth to pulp ratio (Herrman et al, 2020), and pectoral flipper bone ossification (Barratclough et al, 2019). However, all methods vary in inherent accuracy and must be calibrated against some age estimate of the species in question, most often by using GLG counts, and each have limitations for field use and accuracy across different age classes.…”

Long‐Term Immunological Alterations in Bottlenose Dolphin a Decade after the Deepwater Horizon Oil Spill in the Northern Gulf of Mexico: Potential for Multigenerational Effects

“…In a subset of the dolphins examined, a tooth was extracted for age determination using the growth layer group method (Hohn et al 1989). Several dolphins underwent dental radiography for age determination based on pulp‐tooth area ratios (Herrman et al 2020), as validated in humans (Cameriere et al 2007). In all cases, dolphin ages were assessed using a similar combination of methods in Barataria Bay and Sarasota Bay to determine whether or not they were alive at the time of the spill.…”

Multi-tissue methylation clocks for age estimation in the common bottlenose dolphin

“…Compared to recent efforts to develop rapid, non-invasive methods for age determination, including, pectoral flipper bone ossification and dental radiographic determination of the pulp to tooth area ratio which appear to be accurate in juvenile animals[15, 16]. Although bone ossification and pulp to tooth ratios benefit from portability of radiography units that can be used in the field to estimate age within hours of image collection, they still require animal restraint and suffer from reduced accuracy with animals that have reached physical maturity[15, 16]. By contrast, epigenetic clocks apply to the entire life-span of the bottlenose dolphin [1].…”

“…As such, other aging methods have been evaluated for use with bottlenose dolphins or other cetaceans including eye lens aspartic acid racemization[8, 9], fatty acid composition[10–12], radiocarbon 14 dating from fallout[13], telomere length[14], radiograph changes in tooth to pulp ratio[15] and pectoral flipper bone ossification[16]. However, all methods vary in inherent accuracy and must be calibrated against some age estimate of the species in question, most often by using GLG counts, and each have limitations for field use and accuracy across different age classes.…”