AGE DETERMINATION IN MANATEES USING GROWTH-LAYER-GROUP COUNTS IN BONE

Authors

  • Miriam Marmontel,

    1. Department of Wildlife and Range Sciences, University of Florida, Gainesville, Florida 32611
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  • Thomas J. Nhea,

    1. U.S. Fish and Wildlife Service National Ecology Research Center, Sirenia Project, 412 NE 16th Ave., Gainesville, Florida 32601
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    • 2National Biological Service, Midcontinent Ecological Science Center, 4512 McMurry Ave., Fort Collins, Colorado 80525-3400, U.S.A.

  • Howard I. Kochman,

    1. Florida Museum of Natural History, University of Florida, Gainesville, Florida 32611
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  • Stephen R. Humphrey

    1. Department of Wildlife and Range Sciences, University of Florida, Gainesville, Florida 32611
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  • 1Projeto Mamiraua, Av. Brasil, 197, 69470 Tefe AM, Brazil.

  • 3now with National Biological Service, same address.

Abstract

Growth layers were observed in histological preparations of bones of known-age, known minimum-age, and tetracycline-marked free-ranging and captive Florida manatees (Trichechus manatus latirostris), substantiating earlier preliminary findings of other studies. Detailed analysis of 17 new case histories showed that growth-layer group (GLG) counts in the periotic bone were consistent with known age, or time since tetracycline administration, but were less reliable in other bones. GLG counts were also made in periotic bones of 1,196 Florida manatees of unknown age found dead from 1974 through 1991. These counts were conducted in order to assess variability and to determine relationships among estimated age, size, sex, and degree of bone resorption. Resorption can interfere with accuracy of GLG counts. This effect does not occur until ages greater than about 15 yr and body lengths greater than 300 cm are attained. GLGs were also observed in periotic bones of Antillean manatees (Trichechus manatus manatus) but were not validated against known-age specimens. Use of GLG counts in the periotic bone is suitable for application to studies of population dynamics and other age-related aspects of manatee biology.

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