RESULTS AND DISCUSSION 



MANATEES 



Abundance and Distribution 



Two hundred and ninety-seven groups of manatees, totaling 554 individuals, were 

 observed during 12L8 survey hours (Figure 1). Numbers sighted (Table 1) and average 

 number of individuals per group (Table 2) varied by county and month. Total numbers of 

 manatees sighted increased from September to November, but the total per county 

 consistently increased only in Monroe County. Total counts in our study were not 

 statistically compared among counties because habitat type, weather, and amount of 

 survey area were not equivalent. 



From 51 to 100 manatees, representing 54.3 to 75.7% of those sighted on July to 

 November surveys, respectively, and 58.5% overall, were observed in Monroe and Collier 

 Counties (Table 1). Manatees were consistently sighted in Whitewater Bay, Chevalier 

 Bay, and in the Lopez River (ENP, Monroe County), but the largest concentrations were 

 found in Collier County from Marco Island to Chokoloskee. Due to water turbidity 

 (estimated visibility 0-0.5 m) and the complexity of marsh-river habitats, we believe that 

 many manatees were overlooked because they were not near the surface or creating 

 obvious surface wakes or mud trails. 



Odell (1979) sighted from to 71 manatees during transect-surveys conducted 

 from July to December, 1973 through 1976, in Monroe and Collier Counties. Hartman 

 (1974) sighted 45 manatees in Monroe and Collier Counties during a summer survey; Irvine 

 and Campbell (1978) reported observing 163 manatees during a 1976 winter survey of the 

 same area. Although abundance reports by different authors are not completely 

 comparable because of variability among surveys, results of our study clearly support 

 previous reports (Moore 1951a, 1951b, Hartman 1974, Irvine and Campbell 1978) that 

 southwestern Florida is an important center of manatee abundance. Relative abundance 

 of manatees away from warm -water refuges (see below) has been documented in the 

 Banana River, Brevard County, where over 100 manatees were counted during biweekly 

 surveys (Irvine et al. 1978, Shane 1981), but few other warm season counts are available. 



Southerly shifts in the distribution of manatees in Florida during the fall were 

 predicted by Moore (1951b) and Hartman (1974). Although total counts in Monroe and 

 Collier Counties generally increased during fall surveys, the significance of this trend is 

 unclear. Increased sightings may correlate with changes in manatee abundance, but 

 could also indicate that the animals are for some reason more easily observed in that 

 season. In any event, a southerly autumn shift in distribution cannot be conclusively 

 shown based on our data. 



