INTRODUCTION 



West Indian manatees (Trichechus manatus) and bottlenose dolphins (Tursiops 

 truncatus) occur in rivers, estuaries, and coastal areas in Florida (Moore 1953a, Layne 

 1965, Hartman 1974, Irvine and Campbell 1978). Manatees are dispersed during the 

 summer, but concentrate around warm -water sources or in southwestern Florida in 

 winter (Hartman 1974, Irvine and Campbell 1978). Bottlenose dolphins are usually sighted 

 in coastal and estuarine waters of Florida (Moore 1953a, Layne 1965, Odell 1976, 1979, 

 Leatherwood 1979), and may remain in some areas throughout the year (Irvine et al. 

 1979). Seasonal changes in local distribution and abundance have only been documented 

 in a few areas for manatees (Odell 1976, 1979, Irvine et al. 1978, Shane 1981) or dolphins 

 (Odell 1976, 1979, Shane and Schmidly 1978, Irvine et al. 1979). The distribution of 

 manatees and dolphins in various habitat types and salinities in Florida also is unclear. 



Manatees and dolphins are protected by the Marine Mammal Protection Act of 

 1972 and manatees are also protected by the Endangered Species Act of 1973. Areas with 

 high densities of these animals, which would potentially be impacted by Outer 

 Continental Shelf (OCS) development, must therefore be identified. Southwestern 

 Florida, encompassing Everglades National Park (ENP, Monroe County) and the Ten 

 Thousand Islands (Collier-Monroe Counties), is of particular interest because this area 

 has relatively large numbers of manatees (Moore 1951a, Hartman 1974, 1979, Irvine and 

 Campbell 1978) and only minimal human development. Abundance, habitat use, and herd- 

 size data will provide baseline information for comparison with more developed areas. 



Especially over large areas, aerial surveys are the only cost-effective means to 

 census marine mammals. Statewide census flights in probable manatee habitat have been 

 conducted by Hartman (1974) and Irvine and Campbell (1978), and the population in 

 Florida may number as few as 1,000 manatees (Brownell et al. 1978). Comparable surveys 

 for bottlenose dolphins have not been conducted, although results of transect surveys 

 have been reported by Leatherwood (1979) for the Indian and Banana Rivers in eastern 

 Florida, and by Odell and Reynolds (1980) who censused dolphins up to 48 km offshore of 

 western Florida. Counts from any aerial surveys for marine mammals must be viewed 

 with caution, because the number of animals undetected during a survey is never known, 

 and ground truthing techniques are not available (Hartman 1974, Irvine and Campbell 

 1978). The results of nearshore aerial surveys for manatees and dolphins may therefore be 

 only an index of minimum abundance at the time of the survey, but these counts are also 

 useful to show distribution and habitat use. 



We conducted a series of aerial surveys from July to December 1979 to examine 

 the distribution and relative abundance of manatees and dolphins from Bayport, Hernando 

 County , Florida (28°32'N, 82°39'W), south to Flamingo Ranger Station (ENP), Monroe 



