Abstract
An increased number of bottlenose dolphins (Tursiops truncatus) with skin lesions indicative of freshwater exposure stranded in Alabama during Spring 2020. Little is known about the salinity threshold and length of exposure required for lesions to appear. Grossly, these lesions present acutely as combinations of pale, proliferative skin with areas of ulceration and erosions. These lesions progress to multifocal to coalescing erosions with blubber involvement and algal matting in presumably more chronic cases. In this study, stranding location, sex, age class, and presence/absence of skin lesions were analyzed for freshly dead and moderately decomposed dolphins (n=39) stranded between 1 Jan to 31 Aug 2020. Sixteen animals were not included in this study due to advanced state of decomposition. Discharge from the Alabama and Tombigbee Rivers and salinity data from Dauphin Island were examined during the same period to identify freshwater influx trends. A 40-year flood occurred in Mobile Bay between February and March, with the highest rate of discharge occurring in February, 2.4x greater than the 6-month average, and the lowest salinity occurring in March, 8 psu lower than the 6-month average. Fifty-one percent (20/39) of T. truncatus examined had evidence of freshwater-associated lesions. Prevalence of lesions was highest in adults (13 adults, 6 subadults, 1 calf), but did not differ between sexes. Individuals with freshwater lesions primarily stranded in April (n=13) and were more likely to strand in Mobile Bay (n=17) than in the Gulf of Mexico (n=1). The prevalence of freshwater-associated lesions on dolphins stranded in the Mobile Bay estuary, the fourth largest freshwater drainage system in the country, demands further investigation and highlights the importance of stranding response and skin lesion documentation, especially in times of environmental disruptions.
