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Robert A. Garrott, Bruce B. Ackerman, John R. Cary, Dennis M. Heisey, John E. Reynolds III, Patrick M. Rose, J. Ross Wilcox, Trends in Counts of Florida Manatees at Winter Aggregation Sites, The Journal of Wildlife Management, Vol. 58, No. 4 (Oct., 1994), pp. 642-654
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Garrott et al. (1994) studied this question.
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