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An Analysis of Manatee Mortality Patterns in Florida, 1976-81

Thomas J. O'Shea, Cathy A. Beck, Robert K. Bonde, Howard I. Kochman and Daniel K. Odell
The Journal of Wildlife Management
Vol. 49, No. 1 (Jan., 1985), pp. 1-11
Published by: Wiley on behalf of the Wildlife Society
DOI: 10.2307/3801830
Stable URL: http://www.jstor.org/stable/3801830
Page Count: 11
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An Analysis of Manatee Mortality Patterns in Florida, 1976-81
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Abstract

Mortality frequency distributions were analyzed for 406 dead manatees (Trichechus manatus) recovered in Florida from April 1976 through March 1981. Numbers in each major category based on probable circumstances at death were: undetermined, 187; collisions with boats, 87; perinatal/early juvenile with open diagnoses, 58; entrapment in gates of navigation locks and flood-control dams, 35; other human-related causes, 20; natural, 19. Log-linear models were used to test for associations among the variables location, sex, year, season, and cause of death. No significant associations involved more than two variables simultaneously; none involved sex. Significant associations were accounted for largely by increases in numbers of undiagnosed deaths in winter, flood-control dam entrapments in southeastern Florida, and collisions with boats in northeastern Florida, the latter involving a disproportionately large number of adults. High winter mortality occurred in 1977 and 1981. Winter mortality chiefly involved the late juvenile/subadult size class, and numbers of cases showed a negative partial correlation with minimum air temperatures. Some winter deaths may result from metabolic drains on young manatees inexperienced at utilizing thermal refuges. The numbers of human-caused deaths and the projected human population growth in Florida require increased efforts to reduce mortality, provide meaningful sanctuaries, and reach a better understanding of manatee population dynamics and environmental relationships.

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