Short-term Effects of Hurricane Harvey on Bottlenose Dolphins (Tursiops truncatus) in Upper Galveston Bay, TX

From August 26 to 30, 2017, Hurricane Harvey inundated the Galveston Bay estuary in Texas with record-breaking rainfall. As a result, salinity levels in the bay declined rapidly from an average of 14 to < 1 ppt, altering aquatic habitat in the weeks following the storm. Long-term photo-identification monitoring efforts provided an opportunity to undertake a case study describing the effects of this extreme flood event on the bottlenose dolphins (Tursiops truncatus) inhabiting upper Galveston Bay. We compared dolphin encounter rates for the months preceding and following Harvey to a year with no hurricane, examined shifts in habitat-based encounter rates, and evaluated the prevalence and extent of dolphin skin lesions, typically presenting as ulcerated or degraded epidermis. Encounter rates decreased from 1.09 dolphins per linear kilometer (d/km) in August 2017 before Harvey to 0.29 d/km in September 2017 (compared to 0.85 d/km in August 2016 and 0.91 d/km in September 2016). While most dolphins evacuated the upper portion of the bay, many remaining dolphins shifted habitats from shallow open bay to deep channels where salinity increased with depth. Of the dolphins that were sighted in the upper bay during the low salinity event, 96% exhibited at least one lesion and 65% of those dolphins had lesions of medium or high extent (significant increases compared to pre-Harvey levels). After salinity returned to levels above 11 ppt (approximately 8 weeks after Harvey), encounter rates increased and extent of lesions decreased, but prevalence of lesions remained elevated for at least 4 months after Harvey.