15 



There were 28 dolphins considered immigrants in 1991 because they were first 

 identified in 1991 and subsequently in 1992 and 1993. Twelve dolphins had sightings 

 in months outside our census period but no sighting histories in adjacent study areas. 

 One animal had a sighting record outside our artificial Tampa boundary but within 

 the range of its other sightings. Again, approximately half the animals were 

 described as having subtle features and half were considered distinctive with 

 multiple diagnostic features. 



The proportion of dolphins in the catalog that met the criteria for immigration 

 was 0.044 in 1990, and 0.066 in 1991, for an average of 0.055 across both years (Table 

 6). None of these animals was observed outside the Tampa Bay study area prior to 

 their first sighting in the study area, so it was not possible to confirm that they were 

 indeed immigrants, nor was it possible to determine their points of origin. 



Emigration 



Seven dolphins were considered to be emigrants in 1990 because they were 

 identified in each of the first three years of the study but not in the last three years. 

 Two of these animals were identified during the first three years in months outside 

 the survey period. All of their sightings were within the Tampa Bay study area. All 

 were considered distinctive, however none of these potential emigrants was 

 identified from the stranding records or photographs we examined. 



Ten dolphins were identified during each of the first four years of our study 

 but not in the last two years and thus were defined as potential emigrants from 

 Tampa Bay during 1991. Nine of these dolphins were identified in Tampa Bay in 

 months outside the survey period but had no sighting records from the adjacent 

 communities. All were distinctively marked and five had initial sightings between 

 1975 and 1983. 



The proportion of potential emigrants in 1990 was 0.022 of the catalog size for 

 that year, and 0.023 in 1991 (Table 6). None of these animals was seen in other 

 regions after disappearing from the Tampa Bay study area, so it was not possible to 

 confirm that they were actual emigrants, nor was it possible to determine then- 

 destinations because there were no sighting records of these dolphins after 

 disappearing. 



Transience, 



Dolphins identified during only one year of the surveys were defined as 

 transients. There were 12 dolphins that met our criteria in 1990 (Table 6). This was 

 0.038 of the catalog size in 1990. In 1991, 22 dolphins were defined as transients 

 (0.052 of the catalog). None of these animals was seen in the Tampa Bay study area 

 outside of the survey season, nor were they seen in adjacent study areas, so their 

 origins and destinations remain undetermined. 



Discussion 



Photo-Ide ntification Catalog 



The ability to identify individuals over time using natural markings has 

 proved to be a valuable and benign research tool and a standard in population studies 

 of marine mammals. Maintaining a photographic database of individual dolphins 



