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 (Wells 1986). The degree of 

 overlap in home ranges in the Tampa Bay study area varies. 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 are not biologically 

 based. They do 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 Tampa Bay area. 



Natality 



The natality estimate probably underestimates the total number of births in a 

 given year. 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 prep.). Thus, the 

 actual crude birth rate may have been higher than the 0.028 to 0.040 reported from 

 the 1988-1993 surveys. 



The average natality estimate of 0.033 + 0.0909 is slightly lower than that 

 reported for Sarasota Bay. A mean crude birth rate of 0.055 + 0.0089 for Sarasota 

 dolphins was calculated for the period 1980-1987 (Wells and Scon 1990). 

 Observational effort in Sarasota has been ongoing, providing opportunities to 

 observe a higher proportion of births. The narrow window for the Tampa Bay 

 survey means that some calves are likely missed. Thus, the Tampa Bay 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 consistency of the natality rate over the six-year survey period also 

 supports the conclusions drawn from the abundance estimates regarding the 

 stability of the population size. 



Mortality 



Measurements of dolphin mortality rates for Tampa Bay proved to be difficult 

 to obtain during our survey period. In most cases we were unable to distinguish 

 between mortalities, emigrations, undetected fin changes, and animals missed during 

 the Tampa Bay surveys. In Sarasota, it has been possible to evaluate losses from the 

 population from two directions, through the collection and examination of carcasses 

 of identifiable individuals, and through records of disappearances of known 

 individuals (Wells and Scott 1990). Mortality estimates are facilitated in Sarasota as 

 compared to the Tampa Bay project because Sarasota involves a smaller number of 

 dolphins with a higher proportion of them being identifiable, a smaller study area, a 

 more-intensive, year-round monitoring effort, and more-complete and consistent 

 stranding response effort. 



