16 



The CVs for the estimates for the mark-resight method (Method 3) ranged 

 from 0.06 to 0.10, with an average CV of 0.08 for 1990-1994. This would allow an 

 increasing or a decreasing trend to be detected in three surveys. 



Method 4 (resighting-rate method) used the regression analysis described in 

 Method 1 to yield a CV of 0.23. Three survey sessions would be required to detect a 

 decreasing trend and four for an increasing trend. 



Natality 



The natality rate, the proportion of dolphins considered young-of-the-year, 

 varied during the course of the surveys, ranging from 0.020 to 0.050 (Table 5). If 

 these rates are applied to the population size estimates derived by Method 2 (mark- 

 proportion method), then annual estimates of 7 to 17 young-of-the-year are derived 

 for the Charlotte Harbor study area. The mark-proportion estimates are used here 

 because the variances were low, and the estimates for population size and natality 

 were calculated in a similar manner, i.e. on a proportion-of-school basis. 



Mortality 



There were 116 records of stranded animals from South Sarasota, Charlotte, 

 and Lee counties from 1979-1994; 70 of these records were from 1990 to 1994 (Table 6, 

 Figure 9). We were unable to calculate a mortality rate due to the bias associated 

 with an increase in stranding response effort since the mid-1980s. Coastal 

 development and boating activity on Charlotte Harbor waters have also increased 

 dramatically, possibly contributing to the discovery of carcasses in previously 

 isolated areas. However, there are still many remote and inaccessible areas within 

 Charlotte Harbor where carcasses are unlikely to be found. All these factors 

 confound determination of the actual number of strandings and make it impractical 

 to calculate a mortality rate based on stranding records alone. 



In an attempt to distinguish between mortalities and other kinds of losses 

 from the population, photographs of stranded dolphins were examined. A total of 

 30 photographs were available to compare with the photo-ID catalog. Dorsal fins in 

 photographs of 7 animals were deemed non-distinctive, i.e., they belonged to 

 neonates, calves or otherwise had no diagnostic markings. Twenty-three animals 

 were considered distinctive and were used to compare with the photo-ID catalog 

 (Table 6). We identified 2 of the stranded animals: One animal was sighted in the 

 first four years of the Charlotte Harbor surveys and stranded in March of 1994. The 

 other was first identified in 1990 and died in November of 1991. 



Of the 411 dolphins in the 1990-1994 Charlotte Harbor catalog, 165 were not 

 seen during the last year of the study. Two of these (0.012) were confirmed as 

 mortalities based on fin identifications. 



Immigration. Emigration. Residency, and Transience 



We were unable to develop a reasonable quantitative estimate of rates of 

 immigration or emigration for Charlotte Harbor due to the brevity of the study 



