Abstract
<p>This study investigated a bottlenose dolphin community within an urban estuary impacted by anthropogenic stressors. Social structure, genetic structure and organohalogen pollutant (OH) concentrations in bottlenose dolphins ( Tursiops truncatus) in Biscayne Bay, Florida were evaluated. Social structure analysis identified 2-4 overlapping social groups segregated along a north/south gradient. Significant genetic structure was found between 78 Biscayne Bay and 53 Florida Bay dolphins using mitochondrial DNA and 10 nuclear microsatellite markers (FST = 0.14, p<0.01 and FST = 0.04, p<0.01 respectively). Within Biscayne Bay, northern dolphins were significantly differentiated from southern dolphins at microsatellite loci (FST = 0.01, p<0.01), but not at the mitochondrial locus. Spatial autocorrelation analysis within Biscayne Bay found dolphins within 16 km of each other were more closely related than would be expected by chance, indicating significant small scale genetic structure. OH pollutants, including PCBs, DDTs, PBDEs, and other pesticides, were analyzed in blubber samples from 45 dolphins. Total PCBs (Sigma73PCBs) were present in the highest concentrations and were 5 times higher in males with sighting histories in the northern, metropolitan area of Biscayne Bay than males in the southern, more rural area [Geometric Mean: 43.3 (95% CI: 28.0--66.9) vs. 8.6 (6.3--11.9) mug/g wet mass respectively]. All compound classes had higher concentrations in northern animals than southern animals for both male and juveniles combined and adult females.The results of this study have important implications for research and management. The genetic structure found between Biscayne Bay and Florida Bay suggests that the current stock definitions for Atlantic coast bottlenose dolphins are inadequate, and that estuarine dolphin communities should be managed separately. Knowledge of social and genetic structure within Biscayne Bay aids in interpreting the observed fine-scale differences in OH concentrations. The PCB concentrations in northern Bay dolphins are among the highest observed in estuarine dolphins and may place these animals at risk of reproductive failure and decreased immune function. The differences found on this small geographic scale demonstrate that differential habitat use can strongly influence OH concentrations and should be considered when interpreting OH data in relation to both dolphin and ecosystem health.</p>