Louisiana, herd sizes averaged 25.2 dolphins with herd size in marshlands averaging 16.7 

 (Leatherwood and Platter 1979). Subgroups contained a mean of 5 dolphins in sounds and 

 3.8 dolphins in marshes (Leatherwood and Platter 1979). Barham et al. (1980) reported 

 that herd sizes averaged 6.95 dolphins in Texas, and Leatherwood (1979) reported herds 

 averaging 8.20 dolphins in eastern Florida. Differences between observed herd sizes have 

 been attributed to the influence of geography and habitat on dolphin groups structure 

 (Leatherwood and Platter 1979), with largest groups found offshore (Wells et al. 1980). 

 However, criteria for defining "herds" or "subgroups" are rarely reported, and could 

 influence differences in reported results. During our surveys we often encountered 

 several herds within a few km of each other, after not seeing dolphins for distances of 20 

 km or more. Although such assemblages may have been dispersed subgroups of a larger 

 herd, they did not meet our arbitrary criteria for defining a "herd" (see methods 

 section). Our spatial definition of herd may be unsatisfactory if bottlenose dolphins, like 

 some other cetaceans, maintain acoustic contact over many kilometers (Payne and Webb 

 1971). Acoustic contact among free ranging groups of T. truncatus , however, has not 

 been demonstrated, and we know of no more appropriate basis for defining herds from 

 aerial sightings. 



Habitat Use 



Numbers of dolphins observed were not proportional to the amount of survey time 

 in different habitats and salinities (P < 0.005; chi-square). More animals were observed 

 offshore and in salt water (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; chi-square). Most dolphins were sighted offshore in 

 Hernando, 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. 



Calf Sightings 



A maximum of 5.3% of all animals sighted were calves during both the September 

 and December surveys. A high of 12.596 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). 



The proportion of dolphin calves noted during our surveys is low when compared 

 with other reports. Leatherwood (1979) observed 8.1 to 10% calves during aerial surveys 

 in eastern Florida, while Irvine et al.(1979) reported a maximum of 11% from May to July 

 during boat surveys near Sarasota, Florida Shane and Schmidly (1978) noted that calves 

 constituted 7.6% of all dolphin sightings during surface surveys near Port Aransas, Texas, 

 and Barham et al. (1980) sighted 9.3% calves from the air in the same area. Leatherwood 

 (1977) observed 7.7% calves in 1974 and 7.9% calves in 1975 near the mouth of the 

 Mississippi River. Our calf counts may be lower because we only counted very small 

 animals; calves may grow to 2 m long within the first year (Leatherwood 1977), and 

 therefore we may not have distinguished large calves from adults. 



16 



