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

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

Journal of Mammalogy ◽

10.1093/jmammal/gyz079 ◽

2019 ◽

Vol 100 (4) ◽

pp. 1350-1363 ◽

Cited By ~ 1

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.

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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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Touch, Hearing, and Vision of the Florida Manatee, Trichechus manatus latirostris

PsycEXTRA Dataset ◽

10.1037/e598112013-034 ◽

2010 ◽

Author(s):

Gordon B. Bauer ◽

Joseph C. Gaspard ◽

Debborah E. Colbert ◽

Roger L. Reep ◽

David Mann

Keyword(s):

Florida Manatee ◽

Trichechus Manatus ◽

Trichechus Manatus Latirostris

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Seasonal warm-water refuge and sanctuary usage by the Florida manatee (Trichechus manatus latirostris) in Kings Bay, Citrus County, Florida

GIScience & Remote Sensing ◽

10.1080/15481603.2016.1245822 ◽

2016 ◽

Vol 54 (1) ◽

pp. 1-19 ◽

Cited By ~ 2

Author(s):

Danielle C. Sattelberger ◽

Joyce M. Kleen ◽

Aarin-Conrad Allen ◽

Richard O. Flamm

Keyword(s):

Warm Water ◽

Florida Manatee ◽

Trichechus Manatus ◽

Trichechus Manatus Latirostris ◽

Kings Bay

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Florida manatees Trichechus manatus latirostris actively consume the sponge Chondrilla caribensis

PeerJ ◽

10.7717/peerj.8443 ◽

2020 ◽

Vol 8 ◽

pp. e8443

Author(s):

William Fitt

Keyword(s):

Direct Evidence ◽

Chemical Defenses ◽

Chicken Liver ◽

Direct Sunlight ◽

Florida Manatee ◽

Trichechus Manatus ◽

Trichechus Manatus Latirostris ◽

Variable Chemical

The Florida manatee (Trichechus manatus latirostris Linnaeus 1758) actively selects and consumes the “chicken-liver” sponge Chondrilla caribensis. Manatees ate over 10% of C. caribensis on a sample dock, mostly from pylons that received no direct sunlight. Since manatees reportedly eat mostly seagrasses and algae, it was thought that the chlorophyll-a content of the symbiotic cyanobacteria in C. caribensis might be correlated to the amount eaten; however the correlation was not significant (P > 0.05). C. caribensis has variable chemical defenses and round spherasters (spicules), but these do not appear to be effective deterrents to predation by manatees. This is the first direct evidence that manatees actively seek out and consume a sponge.

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