Age estimation and growth layer patterns in teeth of crabeater seals: A comparison of techniques

2020 ◽  
Author(s):  
Julieta Cebuhar ◽  
Javier Negrete ◽  
Silvina Botta
Keyword(s):  
Age Estimation ◽  
Growth Layer ◽  
Comparison Of Techniques ◽  
Crabeater Seals

scholarly journals Validation of Age Estimation in the Harp Seal, Phoca groenlandica, Using Dentinal Annuli

1983 ◽  
Vol 40 (9) ◽  
pp. 1430-1441 ◽  
Author(s):  
W. D. Bowen ◽  
D. E. Sergeant ◽  
T. Øritsland
Keyword(s):  
Outer Layer ◽  
Age Estimation ◽  
Transverse Section ◽  
Age Determination ◽  
Middle Layer ◽  
Harp Seal ◽  
Growth Layer ◽  
Phoca Groenlandica ◽  
Incremental Growth ◽  
Absolute Age

We investigated the validity and accuracy of age estimation in harp seals, Phoca groenlandica, using a sample of 155 known-age teeth from seals age 3 mo to 10 yr. Under transmitted light, transverse sections of harp seal canine teeth showed distinct incremental growth layers (IGLs) in the dentine. The first growth-layer group (GLG), representing Ist-year growth, consists of two IGLs: an outer layer of opaque dentine, bounded by the neonatal line, and an inner layer of translucent dentine. Subsequent GLGs, each representing 1 yr of growth, generally consist of three IGLs: an outer layer of interglobular dentine deposited during the annual molt in April, a middle layer of opaque dentine formed during the northward spring migration (May–June), and an inner layer of translucent dentine formed from July to March. We show that dentinal GLGs can be used to estimate the absolute age of harp seals. The accuracy of the method decreases with age. Only 72.4% of estimates of 0-group seals were correct using only transverse sections. These errors were virtually eliminated (99.0% correct age determination) when the tooth root was examined. Based on a single examination of a transverse section, the probabilities of correctly estimating age are 0.983, 0.889, 0.817, and 0.553 at ages 1, 2, 3, and 4 + yr, respectively, when clearly inaccurate tag-tooth associations are omitted. The respective probabilities are only slightly higher when age is based on the average of five blind readings, being 1.0, 0.889, 0.833, and 0.625. Beyond age 3 yr, existing data are insufficient to estimate reliably the accuracy of age determined by counting GLGs.

A comparison of techniques in age estimation using the third molar

2017 ◽  
Vol 50 (2) ◽  
pp. 74-83 ◽  
Author(s):  
Michelle E. Berkvens ◽  
Scott I. Fairgrieve ◽  
Scott Keenan
Keyword(s):  
Age Estimation ◽  
Third Molar ◽  
The Third ◽  
Comparison Of Techniques

Age estimation in crabeater seals (Lobodon carcinophagus)

2002 ◽  
Vol 258 (2) ◽  
pp. 197-203 ◽  
Author(s):  
R. M. Laws ◽  
A. Baird ◽  
M. M. Bryden
Keyword(s):  
Age Estimation ◽  
Crabeater Seals ◽  
Lobodon Carcinophagus

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

2019 ◽  
Vol 100 (4) ◽  
pp. 1350-1363 ◽  
Author(s):  
Gina L Lonati ◽  
Amber R Howell ◽  
Jeffrey A Hostetler ◽  
Paul Schueller ◽  
Martine de Wit ◽  
...  
Keyword(s):  
Age Estimation ◽  
Wildlife Conservation ◽  
Absolute Error ◽  
Large Sample Size ◽  
Growth Layer ◽  
Florida Manatee ◽  
Data Set ◽  
Photo Identification ◽  
Layer Groups ◽  
Age Estimates

AbstractAges 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.

Age estimation of marine tucuxi dolphins (Sotalia fluviatilis) in south-eastern Brazil

2003 ◽  
Vol 83 (1) ◽  
pp. 233-236 ◽  
Author(s):  
M.C. de O. Santos ◽  
S. Rosso ◽  
R.M.A. Ramos
Keyword(s):  
Body Length ◽  
Growth Curve ◽  
Age Estimation ◽  
East Coast ◽  
Von Bertalanffy ◽  
Growth Layer ◽  
Thin Sections ◽  
Eastern Brazil ◽  
Sotalia Fluviatilis ◽  
Layer Groups

This study reports the age estimation of marine tucuxi dolphins (Sotalia fluviatilis) found dead along the south-east coast of Brazil (24°40′S–25°30′S). The investigated specimens were collected from August 1995 to December 1998. Ages were estimated through the number of Growth Layer Groups (GLGs) from decalcified and stained thin sections of teeth. A total of 36 individuals was investigated. Estimated ages of marine tucuxis varied from zero to 29 years. The growth curve was attained from a modification of the von Bertalanffy equation applied to body length and age data. It was possible to estimate the total length of 97·8 cm in newborns, physical maturity was attained at seven years of age, and an asymptotic length of 179·8 cm.

scholarly journals A review of age estimation methods in marine mammals with special reference to monodontids

2018 ◽  
Vol 10 ◽  
Author(s):  
Fiona L. Read ◽  
Aleta A. Hohn ◽  
Christina H. Lockyer
Keyword(s):  
Age Estimation ◽  
Marine Mammals ◽  
Estimation Methods ◽  
Growth Layer ◽  
Mineral Density ◽  
Relative Age ◽  
Accuracy And Precision ◽  
Absolute Age ◽  
Hard Structures ◽  
Layer Groups

This paper presents a critical review of methods for estimating absolute or relative age in marine mammals. Absolute age is achieved by counting growth layer groups (GLGs) in hard structures such as teeth, ear plugs, baleen, bones and claws. Relative age can be obtained by methods such as aspartic acid racemisation, genetic telomeres, bone mineral density, fatty acid signatures and other methods. Each method is discussed in detail. Accuracy and precision, including inter-reader calibration and anomalies, as well as methods of validating GLG deposition rates are also addressed. Each section concludes with methods of age estimation applicable to monodontids, and suggestions on the focus of future age-estimation research.

scholarly journals An evaluation of age estimation using teeth from South Asian River dolphins (Platanistidae)

2014 ◽  
Vol 8 ◽  
Author(s):  
Christina H Lockyer ◽  
Gill T Braulik
Keyword(s):  
South Asian ◽  
Age Estimation ◽  
Population Biology ◽  
Survival Rates ◽  
Museum Collections ◽  
Age At Maturity ◽  
Growth Layer ◽  
Growth And Survival ◽  
River Habitat ◽  
Layer Groups

The South Asian river dolphins (Platanista gangetica minor and P. g. gangetica) are endangered, geographically isolated, freshwater cetaceans. Accurate age estimation of individuals is an important aspect of population biology as it is used for calculating parameters such as age at maturity and reproduction, longevity, and growth and survival rates. However this has never been comprehensively studied for this endangered cetacean family. A sample of 41 teeth from 29 skulls stored in museum collections was available. We compared two different aging methods to select the most appropriate. This involved decalcification and freeze-sectioning of teeth at variable thicknesses (10–25 micron), and staining with 1) Toluidine Blue, or 2) Ehrlichs Acid Haematoxylin. Stains were then compared for readability of Growth Layer Groups (GLG). The optimum section was found at 20 micron using Erhlichs Acid Haematoxylin. Both dentinal and cemental GLG were readable and comparable, but cemental GLG were generally easier to interpret because they were better defined. Ages varied from newborn / young of year (with none or only a neonatal line present) to a maximum age of 30 GLG. There is currently no validation available for GLG deposition rate, but it is likely annual because of the extreme seasonal changes in the river habitat. 

Sign in / Sign up

Export Citation Format

Share Document