Low-Level Monitoring of Bottlenose Dolphins, Tursiops truncatus, in Charlotte 



Harbor, Florida, 1990-1994 

 Final Report, NMFS Contract 50-WCNF-0-06023 



Randall S. Wells, M. Kim Bassos, Kim W. Urian, William J. Carr, Michael D Scott 



Chicago Zoological Society, Sarasota Dolphin Research Program 



c/o Mote Marine Lab, 1600 Thompson Parkway, Sarasota, Florida 34236 



Executive Summary 



The National Marine Fisheries Service (NMFS) has recognized a need for 

 low-level monitoring of bottlenose dolphin stocks in southeastern U.S. waters, 

 designed to detect catastrophic changes in the stocks. The main goals of the 

 monitoring are detection of large-scale changes in dolphin abundance and 

 establishment of archival databases for long-term trend detection. Low-level 

 monitoring can provide a short-term means of detecting large-scale changes in 

 population abundance and give decision makers the information necessary to 

 determine if modification of management plans is necessary. To these ends, the 

 NMFS has funded several local research efforts in the southeastern U.S., including 

 the photographic identification effort in Charlotte Harbor, Florida, reported here. 

 Charlotte Harbor was of interest to management agencies at least in part because of 

 the use of this region from the 1960s through the 1980s for commercial dolphin 

 collection. More recently, Charlotte Harbor has been designated as a National 

 Estuary under the Clean Water Act. 



Our Charlotte Harbor study area included the inshore waters from Lemon 

 Bav southward to northern Pine Island Sound on the central west coast of Florida. 

 Photographic identification surveys were conducted through the study area on an 

 average of 24 boat-days in August of each year from 1990 through 1994. Mark- 

 resighting analyses modeled after a comparable study in Tampa Bay during 1988- 



1993 allowed eshmahon of abundance and natality, analysis of inter-year trends, and 

 evaluation of seasonal residency. Our Charlotte Harbor photo-ID catalog for 1990- 



1994 included 411 different dolphins. 



During August of each year from 1990 through 1994, an average of about 308 

 dolphins used the Charlotte Harbor study area. The abundance apparently 

 increased from 198 - 369 (95% CLs) in 1990 - 1992 to 315 - 463 in 1993 - 1994. Part of 

 this increase appeared to be due to an increase in reproduction. The average natality 

 across the study years was 0.034, but a peak of 0.050 was reached in 1993. The 

 increase in the proportion of calves from 0.120 in 1990 to 0.210 in 1993 and 1994 

 suggests the successful recruitment of many of the young-of-the year. It was not 

 possible to calculate rates of immigration or emigration. Evidence from the high 

 proportion of animals present in multiple years and the absence of documentation 

 of unidirectional movements between Charlotte Harbor and other adjacent and 

 distant contiguous study areas along the central west coast of Florida indicate that 

 permanent immigration and emigration appear to be rare events. About 9% of the 



