During three Unusual Mortality Events (UMEs), (1999-2000, 2004, and 2005-2006), more than 300 bottlenose dolphins died along the Florida Panhandle.  St. Joseph Bay was the geographic focus of the 2004 mortality event.  The most recent (1994) NOAA’s Fisheries Service abundance estimate for bottlenose dolphins in St. Joseph Bay is zero, but dolphins are currently observed in the region throughout the year.  Thus, critical gaps exist in our knowledge of bottlenose dolphin abundance in this region.  The goals of this study were to estimate seasonal abundance, identify site-fidelity patterns, and determine utilization areas (region in which an animal conducts its normal activities during the study period) of bottlenose dolphins in the St. Joseph Bay region.

“X14” (2001) and  “X16” (2002), the first two cataloged dolphins in the St. Joseph Bay project in April 2004.

       Mark-recapture photo-identification surveys were conducted during each season to estimate abundance using closed and robust population models.  Site-fidelity indices (i.e. the amount of time individuals were spending within the St. Joseph Bay region) were calculated from the total number of sightings of each identified individual during all photo-identification efforts carried out in the region (April 2004-July 2007).  Mark-recapture abundance estimates were highest in spring (327-480) and fall (282 - 462) and lowest in summer (116-176) and winter (122-184).  Individuals with low site-fidelity indices were sighted more often in spring and fall than in summer and winter.  Individuals sighted during summer and winter displayed higher site-fidelity indices. 
                As a result of two NOAA-sponsored bottlenose dolphin health assessments (April 2005, July 2006), 23 dolphins were radio-tagged and monitored for up to three months.  Dolphins tagged in spring 2005 displayed variable utilization areas and variable site-fidelity patterns.  In contrast, during summer 2006, the majority of radio tagged individuals displayed similar utilization areas and moderate to high site-fidelity patterns.  These results suggest that during the summer, St. Joseph Bay hosts dolphins that spend most of their time within this region.  In spring, St. Joseph Bay is visited by dolphins that range outside of this area. 
                These results suggest that the 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 that may represent the resident community of the St. Joseph Bay region.  The impacts of past and potential future UMEs in the St. Joseph Bay region likely are affected by these seasonally variable patterns of habitat utilization.
                This research would not have been possible without funding from NOAA’s Fisheries Service and the Disney Wildlife Conservation Fund.