IRVINE ET AL: AERIAL SURVEYS FOR MANATEES AND DOLPHINS 



and well into Tampa Bay. In the Charlotte-Lee 

 Counties area, dolphins were common in the Gulf 

 of Mexico, around Pine Island, and occasionally 

 in the lower Caloosahatchee River. Most coastal 

 sightings were within 0.5 km of the beach. 



Dolphin herd sizes were not sighted with equal 

 frequency (Fig. 3); most sightings (56%) con- 

 sisted of two or more animals (P<0.005; chi- 

 square). Mean herd size for the pooled sample of 

 all sightings was 3.2 dolphins/herd (SE = ± 0.26). 

 Effects of county and month on average herd size 

 in counties with sightings in each month (Table 

 2) were analyzed as a two-way ANOVA. The 

 county by month interaction was significant 

 (P<0.0005), indicating that monthly variations 

 in dolphin herd sizes were not comparable among 

 counties. A separate one-way ANOVA for each 

 county indicated that monthly variation in herd 

 size was significant (P<0.05) only in Lee County, 

 due to a high December mean. Pooled sightings 

 from all counties indicated that herd size-fre- 

 quency distributions varied significantly be- 

 tween months (P<0.001; chi-square), with fewer 

 single dolphins and more large groups (>4) 

 sighted in July and December. 



Numbers of dolphins observed were not pro- 

 portional to the amount of survey time in differ- 

 ent habitats and salinities (P<0.005; chi-square). 

 More animals were observed off the beach and 

 in saltwater (Table 3), but monthly trends were 

 not apparent. Dolphins were not sighted in fresh- 

 water. Pooled samples from all counties where 



sightings occurred indicated that numbers of 

 dolphins sighted per month varied significantly 

 by habitat and salinity (P<0.001). Most dolphins 

 were sighted offshore in Pinellas and Sarasota 

 Counties; more animals were in bay-estuary than 

 in other habitats in Lee County; and most were 

 in marsh-river habitats in Collier and Monroe 

 Counties. 



A maximum of 5.3% calves was observed dur- 

 ing both the September and December surveys. 

 A high of 12.5% calves was sighted in Monroe 

 County in December, but this total may not be 

 representative because relatively few dolphins 

 were sighted in the area during the abbreviated 

 surveys (Table 1). 



DISCUSSION 



Manatees are usually sighted in small groups 

 when away from warm water refuges. Eighty- 

 six percent of the sightings during aerial surveys 

 by Odell (1979) and 89% of the sightings by Hart- 

 man (1979) were of one to four manatees. Our 

 results and those from other surveys (Hartman 

 1979; Odell 1979; Reynolds 1981) indicate 

 that the greater percentage of manatees sighted 

 are found in groups, but one is the most common 

 group size. Although Hartman (1979) suggested 

 that manatees are "essentially solitary," solitary 

 manatees are nevertheless a minority of the total 

 numbers sighted. 



Odell (1979) sighted from to 71 manatees 



2 

 Z 



O 40 - 



QoQn 



nnnnr, 



a> 



l-l [-1 l—l n I— l,;( l I ;H-t ; l f-l ,;■!-! 



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 27 30 44 72 



HERD SIZE 



FIGURE 3.— Herd size-frequency distribution of bottlenose dolphins sighted during 

 aerial surveys from July through December 1979. 



627 



