Abstract
The Bonnet Carré Spillway was built in 1927 in response to the Great Mississippi Flood. Now the spillway is used to divert water from the Mississippi River into Lake Pontchartrain, which then empties into the Mississippi Sound. Prior to 2019, the Bonnet Carré Spillway had been opened a total of 12 times, with nine of those openings occurring since 1973.1 Since 2011, dolphin strandings average 105 per year when the spillway is opened, compared to 38 strandings when the spillway is not opened. In 2019, for the first time in history, the Bonnet Carré Spillway was opened twice within the year, which yielded 151 dolphin strandings with 46 of those having freshwater-associated lesions and 12 having suspected freshwater-associated lesions. In two dolphins that stranded alive with freshwater-associated lesions, bloodwork was obtained and revealed renal abnormalities (increased BUN and creatinine) and electrolyte imbalances.2 Significant consistent electrolyte imbalances included hyponatremia, hypochloridemia, hyperkalemia, and hyperphosphatemia. Unfortunately, these two dolphins died during the stranding response. Postmortem and histologic evaluations of dolphins with freshwater-associated lesions had major pathology of the skin and brain, with lesser effects on the eyes, joints, liver, adrenal glands, and lungs. Significant consistent lesions included severe epidermal ballooning degeneration with secondary bacterial and fungal dermatitis, adrenal degeneration and apoptosis in the zona glomerulosa, and cerebral edema. In our professional opinion, contributing factors to the increased stranding event in 2019 included sepsis secondary to the extensive skin lesions, electrolyte abnormalities, and widespread edema including epidermal and cerebral edema, which were all secondary to freshwater exposure.
Acknowledgements
The authors wish to thank National Fish and Wildlife Foundation, Mississippi Department of Environmental Quality, Mississippi Department of Marine Resources, Dr. Ruth Ewing from National Oceanic and Atmospheric Administration, Dr. Debra Moore from IMMS, and the IMMS Stranding Team.
*Presenting author
Literature Cited
1. Historic Operations of the Bonnet Carre’ Spillway. (n.d.). Retrieved 2020, from www.mvn.usace.army.mil/Missions/Mississippi-River-Flood-Control/Bonnet-Carre-Spillway-Overview/Historic-Operation-of-Bonnet-Carre
2. Gulland FMD, Dierauf LA, Whitman KL. 2018. CRC Handbook of Marine Mammal Medicine. Boca Raton: CRC Press Taylor and Francis Group. 1124 p.