Seasonal abundance, site-fidelity, and utilization areas of bottlenose dolphins in St. Joseph Bay, Florida

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Brian C. Balmer (Creator)
The University of North Carolina Wilmington (UNCW )
Web Site:
Ann Pabst

Abstract: During three Unusual Mortality Events (UMEs), (1999-2000, 2004, and 2005-2006), a total of more than 300 bottlenose dolphins (Tursiops truncatus) have died along the Florida Panhandle. St. Joseph Bay, in Gulf County, was the geographic focus of the 2004 mortality event. The most recent NOAA abundance estimate for bottlenose dolphins in St. Joseph Bay, based upon aerial surveys conducted in 1994, is zero (Waring et al. 2000). Thus, there exist critical gaps in our knowledge of bottlenose dolphin abundance in this region. The goals of this study were to estimate seasonal abundance and to identify site-fidelity patterns of coastal bottlenose dolphins in the St. Joseph Bay region. Mark-recapture photo-identification surveys were conducted during February/March, April, May, and July 2005 as well as February and September/October 2006 to estimate seasonal abundance in and around St. Joseph Bay. Seasonal abundance estimates were determined using closed and robust population models in the programs MARK and CAPTURE. A site-fidelity index was calculated from the total number of sightings of each identified individual during all photo-identification efforts carried out in the region (from April 2004-October 2006). Abundance estimates were highest in spring (279 - 460) and fall (295 - 376) and lowest in summer (101 - 178) and winter (81 - 126). Site-fidelity indices also varied by season; on average individuals with low site-fidelity indices were sighted more in spring and fall than in summer and winter. The relatively small number of individuals sighted during summer and winter displayed high site-fidelity indices. These results suggest that the potential impacts of UMEs in the St. Joseph Bay region will vary by season. During spring or fall a UME will likely affect both those dolphins with high site-fidelity indices, as well as dolphins moving into or through the region, and, thus, may have a wider regional impact. Mortality events that occur during summer and winter will be focused on a smaller number of individuals with high site-fidelity to the St. Joseph Bay region. Since 1999, three Unusual Mortality Events have occurred along the Florida Panhandle, resulting in more than 300 bottlenose dolphin (Tursiops truncatus) deaths. St. Joseph Bay, Florida was the geographic focus of the 2004 unusual mortality event. Recent mark-recapture photo-identification surveys have demonstrated that dolphin abundance varies across seasons in this region- abundance estimates are highest in spring and fall, and lowest in winter and summer. Most dolphins sighted in spring and fall had low site-fidelity indices, while most sighted in summer and winter had high site-fidelity indices to the St. Joseph Bay photo-id region. Until this study, no information was available on movement patterns of individual bottlenose dolphins in this region of the Florida Panhandle. In this study 23 dolphins were radio tagged and monitored intensively for up to three months following NOAA-sponsored bottlenose dolphin health assessment studies during April 2005 and July 2006. Individual utilization areas (UAs) (i.e. region an individual conducts its daily activities during a study period) and site-fidelity indices were compared across radio tracking periods. An individual’s site-fidelity index was calculated as the proportion of survey months that it was sighted, relative to the total number of months surveys were conducted in the region. Dolphins tagged in spring 2005 displayed three different UA patterns- those extending largely outside the St. Joseph Bay photo-id region (n=2), those partially overlapping this region (n=2), and those completely within the region (n=2). In contrast, during summer, radio tagged individuals displayed only two UA patterns, those partially overlapping the region (n=2) and themajority were those completely within the St. Joseph Bay region (n=11). Individual site-fidelity indices in spring were lower (mean 10.54, range 0.11-1.0) than in summer (mean 0.76, range 0.38-1.0). These results, along with those of Balmer (Chapter 1) suggest that during the summer, when abundance estimates are relatively low, the St. Joseph Bay region hosts a group of dolphins that spend most of their time within this geographic area. In spring, when dolphin abundance increases, St. Joseph Bay is visited by dolphins that will range far, and spend most of their time outside this region. The past and potential future impacts of Unusual Mortality Events on bottlenose dolphins in the St. Joseph Bay region likely depend upon these distinct seasonal patterns of habitat utilization.

Additional Information

A Thesis Submitted to the University of North Carolina at Wilmington in Partial Fulfillment of the Requirement for the Degree of Masters of Science
Language: English
Date: 2009
Bottlenose dolphin--Florida--St.Joseph Bay, Bottlenose dolphin--Geographical distribution, Bottlenose dolphin--Seasonal distribution
Bottlenose dolphin -- Florida -- St.Joseph Bay
Bottlenose dolphin -- Geographical distribution
Bottlenose dolphin -- Seasonal distribution

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