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Because manatees (Trichechus manatus) are large aquatic herbivores they have often been considered as potential control agents for aquatic plants. Several problems are associated with this concept, and a major one has been the gap in knowledge concerning food consumption rates of manatees. We estimated food consumption by measuring chews per unit time, chews per amount of food consumed, and time spent chewing food. Data were collected on captive manatees of various sizes and used to construct regression equations that predict consumption rates based on body size. Time budget data were obtained by radiotelemetry of free-ranging animals. Estimates of consumption rates for manatees eating hydrilla (Hydrilla verticillata Royle) were compared to the estimates biomass of hydrilla in Kings Bay, Florida, the overwintering site for a large manatee populations (116 in the winter of 1980-1981). Estimates show that nearly ten times as many manatees would have been needed just to consume the standing biomass of hydrilla. The inefficiency of manatees as control agents for aquatic plants becomes even more apparent when plant productivity is included in these estimates.

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