Extremely high concentrations of persistent organochlorine contaminants (POCs or POPs) have been measured in bottlenose dolphins from the Georgia coast, particularly in dolphins sampled from the Turtle/Brunswick River Estuary (TBRE) in Glynn County, Georgia. Potential sources for the contamination include four National Priority List sites located in Brunswick, Georgia. The high contaminant levels have raised concerns for the health of this protected species in this region and have prompted questions as to the movement of the POCs through the food web and adjacent estuaries. Dolphins sampled over 40 km northeast of the Brunswick area in the Sapelo Island National Estuarine Research Reserve (SINERR) were found to have POC concentrations that exceeded levels previously measured from any other area of the U.S. coast. While the measures of dolphin contaminant concentrations will provide important information on bioavailable contaminants in the food web, understanding site fidelity and movement patterns of dolphins between the two areas is critical for accurate interpretation of data.
Therefore, in February 2008 a photo-identification study was initiated to characterize the bottlenose dolphin communities near SINERR and within TBRE. The objectives of the photo-identification study were to estimate dolphin abundance, identify site fidelity indices for individual dolphins in each area, quantify movements between locales, and classify habitat utilization at each site. Photo-identification surveys were conducted each season during 2008 and 2009. Preliminary abundance estimates in 2008 were highest in both SINERR and TBRE during spring and summer and lowest in fall and winter. Individuals sighted in spring and summer also had lower site fidelity indices than other seasons. These preliminary results may suggest overlapping stocks (coastal and estuarine) of bottlenose dolphins in both regions.
In addition to the photo-identification study, a capture-release health assessment of bottlenose dolphins was conducted in August 2009 to examine potential health impacts from POC exposures. Aside from assessing health endpoints, an objective of this project was to identify fine scale movement patterns of individual dolphins to allow for correlation of measured POC concentrations with potential exposure sources. With the help of DRCI staff, 28 dolphins were tagged with small VHF radio transmitters. The 28 radio-tagged dolphins were monitored daily through vessel-based tracking for the transmission duration of the radio tags. Vessel-based tracking is effective in obtaining single locations for individual animals daily. However, this technique is labor intensive, the geographic range of tracking coverage is limited, and it is logistically infeasible to perform 24 hours a day. Fourteen experimental remote receivers were positioned along 90 kilometers of coastline in the area to offset the limitations of vessel-based tracking. The benefits of these receivers included: increased number of daily locations, the ability to alert the field team to animals’ locations based on real-time notifications, and an extended geographic tracking coverage.
Three radio-tagged individuals were also instrumented with prototype, satellite-linked transmitters. The goals of this new design were to maximize transmission duration while minimizing long-term effects on the tagged animal. Each satellite-linked tag transmitted location data for over 58 days. The single-pin attachment coupled with relatively small (40g) tags resulted in minimal long-term impacts on tagged individuals. The use of these new and innovative tools in conjunction with conventional radio tracking techniques increases our ability to assess fine scale spatial distribution of marine mammals. This research would not be possible without the commitment of Brian Balmer’s time by the Chicago Zoological Society, and funding from NOAA Fisheries and the Georgia Department of Natural Resources.