Comparison of age determination techniques for known-age Cape fur seals

Abstract

Known-age teeth were used to validate age determination techniques for the Cape fur seal (Arctocephalus pusillus pusi/lus). Thin sectioning and staining of decalcified teeth produced the poorest age estimates. For etched half canines, only upper canines could be used to estimate age with good results, and coating improved the accuracy. Scanning electron microscopy produced poor accuracy in age estimation. External ridges reflected age accurately only in younger age classes and should only be used to verify counts of internal growth layer groups, or when rapid, preliminary estimates of age are necessary. This study has highlighted the importance of comparing different age determination techniques and validating such techniques with known-age anImals. The reliability with which age can be estimated for the Cape fur seal has also been improved.

Canine morphometrics as a tool for distinguishing species, sex, and age class in Southern Ocean fur seals

“…Several studies showed different upper age limits at which age determination by external ridge counts becomes inaccurate. Payne (1978) years and older (Oosthuizen & Bester, 1997). When comparing GLG counts to the true age of known-age females (tagged at 6 weeks of age), age estimates from the GLG counts appeared to underestimate age, likely due to poor sample preparations (Oosthuizen, 1997).…”

“…2009). (Oosthuizen & Bester, 1997). In the few cases where teeth had closed pulp cavities in older individuals, the age was then recorded by counting to the last visible ring.…”

“…Mammalian tooth morphology is diverse and has been used successfully to determine species (e.g., Balasse & Ambrose, 2005 ), sex (e.g., Vodanović et al, 2007 ), age (e.g., Chevallier et al, 2017 ; Richardson et al, 1995 ; White et al, 2016 ), body size (e.g., Gingerich et al, 1982 ; Read et al, 2018 ), and diet (e.g., Chemisquy et al, 2021 ; Tarquini et al, 2020 ; Uchida, 1998a ). Marine mammals are no exception, with tooth morphology having been used to inform on age (e.g., Jeglinski et al, 2010 ; Oosthuizen & Bester, 1997 ; Read et al, 2018 ), sex (e.g., Ramos et al, 2000 ), and diet (e.g., Ford et al, 2011 ; Purnell et al, 2017 ) of various species. Further, many marine mammals, particularly cetaceans and pinnipeds, are born with permanent dentition which represents the full postnatal record of that animal (Kubota et al, 2000 ; Read et al, 2018 ).…”

“…Teeth of pinnipeds grow continuously throughout life, with new layers of dentine being deposited on the inside of the pulp cavity until it closes in older adults (e.g., Boyd & Roberts, 1993 ; Hohn & Fernandez, 1999 ; Lowry & Folk, 1990 ; Read et al, 2018 ). Each one of these growth layers can be seen externally as ridges on the root of the tooth (EARs: external annular ridges) and internally as growth layer groups (GLGs) on longitudinally sectioned teeth (Boyd & Roberts, 1993 ; Lowry & Folk, 1990 ; Oosthuizen & Bester, 1997 ). These annual accumulations represent a year in the life of the animal with dentinal age being close to true age (Hohn et al, 1989 ; Oosthuizen & Bester, 1997 ).…”

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

“…Thus, researchers have developed a variety of methods in an attempt to estimate age in marine mammals, each giving varying accuracy and precision. These techniques include, but are not limited to, long term photographic-identification (photo-ID) monitoring in live animals [1], morphometric comparisons in live and dead animals [2][3][4], dentinal growth layer groups from extracted teeth (GLGs) [1,3,5,6], bone GLGs in carcasses [7,8], skeletal ossification live dolphins [9], bone density [10][11][12], micro-CT scanning [13], radiometric aging in auditory bullae from carcasses [14], ear plug layers in mysticete carcasses [15], aspartic acid racemization in carcasses [16][17][18], baleen length or radiocarbon dating in carcasses [19,20], bomb radiocarbon dating in extracted teeth for animals alive in the 1960s [18,21], telomere sequence analysis in live animals [22][23][24], DNA methylation analysis in live animals [25], and fatty acid signatures in live or dead animals [26][27][28][29]. Unfortunately, many of the aforementioned techniques are inapplicable for use in studies with living dolphins, are unsuitable to be used in field studies, and/or provide poor precision.…”