August of each year. The estimates are based on a catalog that includes all of those 

 dolphins for which satisfactory identification photographs were obtained during the 

 survey period, without distinguishing between differences in the degree of use of 

 the study area waters by different dolphins. 



The catalog makes no distinction between those dolphins using the waters of 

 the study area on a regular basis vs. those photographed during an infrequent 

 passage through the study area. A number of overlapping home ranges occur along 

 the central west coast of Florida, including Tampa Bay, Sarasota Bay, and Charlotte 

 Harbor (Wells 1986), and home ranges apparently exist in Pine Island Sound (Shane 

 1987). The degree of overlap in home ranges in the Charlotte Harbor study area 

 appears to vary. The probability of finding a given dolphin occupying a partially 

 overlapping home range would be a function of the degree of overlap. The limits of 

 our study area were not biologically based. They did not necessarily coincide with 

 home range boundaries, for example, and therefore do not address the relative 

 importance of waters and habitat features in the study area. Evaluation of the 

 biological basis of population units has important management implications, but 

 this requires more-detailed analysis of the community structure of dolphins in the 

 Charlotte Harbor area. 



Natality 



Natality is likely underestimated because, if a diffuse calving season is 

 assumed, then it is likely that some young calves were lost prior to each annual 

 survey, and some may have been born after the survey. A spring through early fall 

 peak in calving with occasional births occurring at anytime during the year has been 

 reported for Sarasota Bay (Wells et al. 1987) and for the west coast of Florida in 

 general (Urian et al.. in press). Thus, the actual crude birth rate may have been 

 higher than the 0.020 to 0.050 reported from the 1990-1994 surveys. 



The average Charlotte Harbor natality estimate of 0.034 for the period 1990- 

 1994 is comparable to that reported for Tampa Bay for 1988-1993 (0.033 ± 0.0909, 

 Wells et al. 1995), and slightly lower than that reported for Sarasota Bay (0.055 + 

 0.0089 for Sarasota dolphins was calculated for the period 1980-1987 (Wells and Scott 

 1990). Observational effort in Sarasota has been ongoing, providing opportunities to 

 observe a higher proportion of births. The narrow window for the Charlotte Harbor 

 survey means that some calves are more likely to be missed. Thus, the Charlotte 

 Harbor natality measure should be compared to a Sarasota measure between the 

 crude birth rate and the recruitment rate (the proportion of calves surviving to age 

 1). For Sarasota Bay, the mean recruitment rate for 1980-1987 was 0.048 + 0.0085 

 (Wells and Scott 1990). Therefore, a comparable measure of Sarasota natality might 

 be between 0.048 and 0.055. 



The variation in the natality rate over the five-year survey period also 

 supports the conclusions drawn from the abundance estimates regarding the 

 increase in population size. 



