14 



(Figures 2a-e). The total number of sightings and dolphins seen each year closely 

 track the level of survey effort (Figure 3). On average, six or seven photographs per 

 dolphin were taken each year. These results compare favorably with those of the 

 Tampa Bay survey project (Wells, et al, 1995). 



Photo-ID Catalog Dev elopment 



The level of survey effort was considered sufficient to warrant generation of 

 abundance estimates based on mark-resighting analyses. This conclusion was 

 supported by the high proportion of identifiable dolphins in the population (58% to 

 80%, Table 3), and the frequency distribution of resightings of identifiable dolphins 

 within survey years (Figures 4a-e). About one quarter of the dolphins were sighted 

 at least twice during a given survey year, up to a maximum of 8 times each. 



Our Charlotte Harbor catalog for 1990-1994 included 411 different dolphins. 

 The catalog size provides a minimum population estimate for the Charlotte Harbor 

 study area ranging from 165 identifications in 1992 to 243 in 1994. On average, 55% 

 of the dolphins in an annual catalog were also seen in either the previous or 

 subsequent year, 51% were seen two years earlier or later, 51% were seen three years 

 earlier or later, 50% were seen four years earlier or later (Table 4). 



Photographs taken during the 1990-1994 NMFS surveys built upon an existing 

 Charlotte Harbor catalog initiated in 1982 (Figure 5; Wells 1986). Of the animals 

 identified prior to the initiation of the surveys, 16 individuals were sighted 

 subsequently during the surveys in 1990-1994. As expected, during the initial years 

 of the surveys many identified dolphins were added to the catalog. New fins were 

 added to the catalog at a slower rate during subsequent years (Figure 5). The 

 proportion of first-time identifications comprising the annual catalog each year 

 declined from 99% in 1990 to 14% in 1994. These results are comparable to those 

 from the Sarasota community (Wells and Scott 1990) and Tampa Bay (Wells et al. 

 1995), suggesting a relatively closed population for the Charlotte Harbor study area. 

 Identifications added to the catalog over the years may represent changes to the fins 

 of known animals, non-distinctive calves acquiring new markings (only a small 

 number of calves are in our catalog), or animals that may have been missed in 

 previous years. We found that overall there were few changes to fin markings 

 throughout the surveys, and minor changes could be detected by a skilled observer 

 familiar with the catalog. However, dramatic changes to fin markings could easily 

 be undetected and could result in a previously identified animal being entered twice 

 in the catalog. 



The stability of fin markings over time enhances the probability of resighting 

 individuals. The high frequency of resighting individuals and the long-term 

 sighting histories suggestt i high degree of residency for some animals in the 

 Charlotte Harbor study area during the survey period (Figure 6). The consistency of 

 the catalog and stability of fin markings over time contribute to our confidence in 



