FISHERY BULLETIN: VOL. 80, NO. 3 



during transect surveys conducted from July to 

 December 1973 through 1976 in Monroe and 

 Collier Counties. Hartman (footnote 3) sighted 45 

 manatees in Monroe and Collier Counties during 

 a summer survey; Irvine and Campbell ( 1978) re- 

 ported observing 163 manatees during a 1976 

 winter survey of the same area. Although abun- 

 dance reports by different authors are not com- 

 pletely comparable because of variability among 

 survey methodologies, results of our study clear- 

 ly support previous reports that southwestern 

 Florida is a center of manatee abundance (Moore 

 1951; Hartman footnote 3; Irvine and Campbell 

 1978). 



Southerly shifts in the distribution of mana- 

 tees in Florida during the fall were predicted by 

 Moore (1951) and Hartman (footnote 3). Al- 

 though total counts in Monroe and Collier Coun- 

 ties generally increased during fall surveys, the 

 significance of this trend is unclear. Increased 

 sightings may correlate with changes in mana- 

 tee abundance, but could also indicate that the 

 animals are for some reason more easily ob- 

 served in that season. In any event, a southerly 

 autumn shift in distribution cannot be conclu- 

 sively shown based on our data. 



The preponderance of manatee sightings in 

 brackish water and marsh-river habitats occur- 

 red in the areas of Collier and Monroe Coun- 

 ties, which are characterized by that combina- 

 tion of habitat and salinity. Inland bays in ENP 

 and Ten Thousand Islands area of Collier County 

 were classified as "marsh-river" habitat because 

 access to the Gulf of Mexico is restricted by 

 relatively narrow or shallow channels. Although 

 the survey results may be general indicators of 

 habitat use, they should be viewed with some 

 caution because all habitat types were not sur- 

 veyed equally, and local salinities may have 

 varied seasonally due to runoff from rainfall. 

 Irvine and Campbell (1978) reported the relative 

 frequencies of manatee sightings in fresh, brack- 

 ish, and salt water as 19.1, 42.5, and 38.3%, re- 

 spectively, during winter surveys, and 35.2, 34.9, 

 and 29.6% during a summer survey of the entire 

 state. In contrast, 80% of the manatees sighted 

 in our surveys were in brackish water (Table 3). 



The few sightings in Charlotte Harbor are 

 noteworthy because manatees are often sighted 

 by residents in this area (Moore 1951; Hartman 

 footnote 3), and 36 manatees were counted in 

 Charlotte Harbor during a summer aerial sur- 

 vey by Hartman (footnote 3). Manatee use of the 

 Bartow and Anclote power plants has not been 



specifically reported, but two sightings mapped 

 by Irvine and Campbell (1978) were at these 

 plants. 



We sighted few manatee calves (4.9% maxi- 

 mum per survey) compared with other surveys. 

 Calves made up 5.2% of the animals sighted by 

 Odell (1979) in Collier and Monroe Counties in 

 1973 through 1976, but during a 1976 winter sur- 

 vey of the same area, 10.4% of the manatees 

 sighted were calves (Irvine and Campbell 1978). 

 Leatherwood (1979) counted 9.9% calves in the 

 Indian and Banana Rivers in eastern Florida, 

 and Irvine and Campbell (1978) reported overall 

 calf percentages of 9.6% in winter and 13.4% in 

 summer from surveys of the entire state. Odell 

 (1979) suggested that the tendency of calves to 

 stay close to their mothers might result in fewer 

 calf sightings in turbid waters, but this hypo- 

 thesis has not been verified. Too few calves were 

 sighted in our study to indicate seasonal repro- 

 ductive trends. 



The dolphin sightings are of particular inter- 

 est due to the paucity of information on T. 

 truncatus in nearshore areas of western penin- 

 sular Florida. The sightings were not analyzed 

 for abundance and density estimates (see dis- 

 cussion by Leatherwood et al. 1978), because 

 flight routes were designed to optimize manatee 

 sightings and were not flown as straight lines. 

 Our observations can, however, provide informa- 

 tion on dolphin herd size and habitat use. 



Average herd size (3.2 dolphins/herd) was con- 

 siderably smaller than herd sizes reported from 

 other aerial surveys in nearshore areas. In 

 coastal waters of Alabama, Mississippi, and 

 Louisiana, herd sizes averaged 25.2 dolphins 

 with herd size in marshlands averaging 16.7 

 (Leatherwood and Platter footnote 10). Sub- 

 groups contained a mean of 5 dolphins in sounds 

 and 3.8 dolphins in marshes (Leatherwood and 

 Platter footnote 10). Barham et al. (1980) re- 

 ported that herd sizes averaged 6.95 dolphins in 

 Texas, and Leatherwood (1979) reported herds 

 averaging 8.20 dolphins in eastern Florida. In 

 primarily estuarine areas of western Florida, 

 group size (equivalent to herd size as used here) 

 was 4.8 dolphins/group (Irvine et al. 1981). 

 Differences between observed herd sizes have 

 been attributed to the influence of geography 

 and habitat on dolphin groups structure (Leath- 

 erwood and Platter footnote 10), with largest 

 groups found offshore (Wells et al. 1980). How- 

 ever, criteria for defining "herds" or "subgroups" 

 are rarely reported, and could influence differ- 



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