The Florida Panhandle coastline has been repeatedly exposed to pollution, infectious disease, red tide events and most recently the DeepWater Horizon oil spill. Over 1200 bottlenose dolphins (Tursiops truncatus) have stranded (95% dead) from the Texas/Louisiana border to the Panhandle since February, 2010. Pensacola Bay, in particular, has been described as one of the most heavily polluted bays in Florida. Our ability to evaluate threats to dolphin populations is impeded by the paucity of baseline population dynamics data. There is a need for population assessments in this area to meet both management needs for stock structure analyses in a previously understudied area and to determine if there are threats to dolphin populations in this system.
The goals of this study were to estimate seasonal abundance and quantify seasonal site fidelity and residency patterns for bottlenose dolphins in the Pensacola Bay system. We performed mark-recapture analyses via photo-identification using Pollock’s robust design and best fit models in program MARK. Site fidelity indices were estimated based on the frequency of individual re-sights within and across seasons. Seasonal abundance is expected to vary with either the distributional shifts of residents in and out of the system or with a seasonal influx of non-residents.
Results/Conclusions
Estimates of bottlenose dolphin abundance in the Pensacola Bay system was 152 (± 19.74 SE) in the summer of 2013, 200 (± 36.52 SE) in the fall of 2013, and 237 (± 93.71 SE) in the spring of 2014.These preliminary data demonstrate peaks in abundance during the fall and spring and a low in the summer, similar to that reported in other areas of the Florida Panhandle. However, preliminary site fidelity indices do not indicate seasonal variation in the proportion of non-residents visiting the system, suggesting a difference in seasonal movement patterns compared to other Florida Panhandle areas. The number of re-sights we have per individual is currently low, potentially masking any real variation. We plan to include additional seasons of data in our analyses to improve the power to detect seasonal variation in site fidelity patterns.
An organism’s seasonal movement patterns can greatly influence resource acquisition, breeding opportunities, exposure to environmental stressors, and other factors that can influence individual survival and fitness as well as population viability. In addition to providing updated stock assessments to resource managers, our results will contribute towards a growing body of literature necessary to better understand the mechanisms behind bottlenose dolphin seasonal movement patterns.