Age estimation in giant otters (Pteronura brasiliensis) (Carnivora: Mustelidae) using growth layer groups in canine teeth

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.

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

Journal of the Marine Biological Association of the United Kingdom ◽

10.1017/s0025315403007021h ◽

2003 ◽

Vol 83 (1) ◽

pp. 233-236 ◽

Cited By ~ 10

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.

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

NAMMCO Scientific Publications ◽

10.7557/3.4474 ◽

2018 ◽

Vol 10 ◽

Cited By ~ 6

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.

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

NAMMCO Scientific Publications ◽

10.7557/3.3268 ◽

2014 ◽

Vol 8 ◽

Cited By ~ 2

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.

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Inter-lab comparison of precision and recommended methods for age estimation of Florida manatee (Trichechus manatus latirostris) using growth layer groups in earbones

NAMMCO Scientific Publications ◽

10.7557/3.3786 ◽

2016 ◽

Vol 8 ◽

Cited By ~ 1

Author(s):

Katherine Brill ◽

Miriam Marmontel ◽

Meghan Bolen-Richardson ◽

Robert EA Stewart

Keyword(s):

Age Estimation ◽

Effective Management ◽

Growth Layer ◽

Florida Manatee ◽

Trichechus Manatus ◽

Trichechus Manatus Latirostris ◽

Apparent Source ◽

Layer Groups ◽

Age Estimates ◽

Good Agreement

Manatees are routinely aged by counting Growth Layer Groups (GLGs) in periotic bones (earbones). Manatee carcasses recovered in Florida between 1974 and 2010 provided age-estimation material for three readers and formed the base for a retrospective analysis of aging precision (repeatability). All readers were in good agreement (high precision) with the greatest apparent source of variation being the result of earbone remodelling with increasing manatee age. Over the same period, methods of sample preparation and of determining a final age estimate changed. We examined the effects of altering methods on ease of reading GLGs and found no statistical differences. Accurate age estimates are an important component for effective management of the species and for better models of population trends and we summarize the currently recommended methods for estimating manatee ages using earbones.

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Ageing live New Zealand sea lions (Phocarctos hookeri) using the first post-canine tooth

Wildlife Research ◽

10.1071/wr03006 ◽

2004 ◽

Vol 31 (2) ◽

pp. 177 ◽

Cited By ~ 20

Author(s):

S. Childerhouse ◽

G. Dickie ◽

G. Hessel

Keyword(s):

New Zealand ◽

Age Estimation ◽

Growth Layer ◽

Canine Tooth ◽

Sea Lions ◽

Glass Slides ◽

Significant Difference ◽

Layer Groups ◽

Phocarctos Hookeri ◽

Age Estimates

Live New Zealand sea lions (Phocarctos hookeri) were aged from growth layer groups (GLGs) in the cementum of a lower first post-canine tooth. A single post-canine (PC1) was removed from individuals of known-age (n = 74) between 1997 and 2001 while under a full anaesthetic. Teeth were decalcified, sectioned on a cryostat, stained and then mounted on glass slides. Age was estimated by counting GLGs in the cementum multiple times. Age estimates were calibrated with known-aged individuals and confirmed the annual formation of cementum annuli in PC1 tooth. While there is some variation in assigning exact age to individuals, it was possible to age 94% of teeth to the exact year or to within 1 year of actual age. There was no significant difference in the slope of regression lines associated with actual and estimated age using this technique (t-test, t = 0.309, d.f. = 144, P < 0.05). Accuracy in ageing was improved by discarding sets of readings with low precision and re-reading the tooth until a precise set of estimates was made. GLGs in the cementum were more accurate and robust for age estimation than using GLGs in the dentine. This paper describes a reliable method for the preparation and ageing of the first post-canine tooth (PC1) from live New Zealand sea lions.

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GROWTH LAYER GROUPS (GLGs) IN THE TEETH OF AN ADULT BELUKHA WHALE (DELPHINAPTERUS LEUCAS) OF KNOWN AGE: EVIDENCE FOR TWO ANNUAL LAYERS

Marine Mammal Science ◽

10.1111/j.1748-7692.1987.tb00148.x ◽

1987 ◽

Vol 3 (1) ◽

pp. 14-21 ◽

Cited By ~ 16

Author(s):

Arthur D. Goren ◽

Paul F. Brodie ◽

Stephen Spotte ◽

G. Carleton Ray ◽

H. W. Kaufman ◽

...

Keyword(s):

Delphinapterus Leucas ◽

Growth Layer ◽

Layer Groups

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Growth of the skull of the bottlenose dolphin, Tursiops truncatus, in the Southwest Atlantic Ocean

Latin American Journal of Aquatic Mammals ◽

10.5597/00229 ◽

2017 ◽

Vol 11 (1-2) ◽

pp. 199-211 ◽

Cited By ~ 3

Author(s):

André Silva Barreto

Keyword(s):

Bottlenose Dolphin ◽

Tursiops Truncatus ◽

Growth Equation ◽

Growth Layer ◽

Southwest Atlantic ◽

Development Patterns ◽

Skull Measurements ◽

The One ◽

Layer Groups ◽

Mature Size

Defining the age of attainment of physical maturity is important for many studies, including identification of stocks, populations or species. In order to identify the age when the skull of the bottlenose dolphin, Tursiops truncatus, reaches maturity, skulls of fifty-three specimens found stranded along the coasts of southern Brazil, Uruguay and northern Argentina (27o35’S, 48o34’W-36o49’S, 55o19’W) were analyzed. Sixty skull measurements were taken to compare the growth rate of the different functional apparatuses. Age was estimated by counts of growth layer groups in the dentine of decalcified, stained longitudinal sections of teeth. Von Bertalanffy’s equation was applied to assess the growth and determine the age at maturity of each apparatus. Generally the maturation of skull starts at age two and stabilizes at age five, and the age of reaching the mature size varies amongst different characters. The braincase is the most precocious apparatus, while the feeding is the one that last stabilizes. The development patterns observed for the hearing, vision and breathing apparatuses were similar. Statistic analysis revealed significant differences among the ages at maturity, but not for von Bertalanffy’s growth equation parameters for each functional apparatus. For the studied population it is suggested that skulls can be considered mature in animals with more than five years.

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

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f83-165 ◽

1983 ◽

Vol 40 (9) ◽

pp. 1430-1441 ◽

Cited By ~ 65

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.

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