[MARMAM] New Paper: Freshwater skin disease in dolphins, a case definition based on pathology and environmental factors in Australia

Padraig Duignan duignanp at TMMC.org
Thu Dec 17 19:57:10 PST 2020

Dear Marmam members,

We would like to bring your attention to a new TMMC/Murdoch/MMF paper on the detrimental effects of freshwater exposure in coastal bottlenose dolphins which is an emerging cause of morbidity and mortality in many parts of the world. In this study we provide a case definition for freshwater skin disease (FWSD) based on two outbreaks that occurred in Australia. The first affected Burrunan dolphins (Tursiops australis) in Victoria’s Gippsland Lakes in 2007.  Coincidentally,  a similar event is occurring there at the present time (see https://www.abc.net.au/news/2020-11-20/burrunan-dolphin-deaths-in-gippsland/12900270). The second event occurred in 2009 and affected the resident Indo-Pacific bottlenose dolphins (T. aduncus) in the Swan and Canning Rivers.  Simultaneous with the Gippsland Lakes outbreak, the first FWSD outbreak in US waters was recorded for common bottlenose dolphins (T. truncatus) entrapped in Lake Pontchartrain, Louisiana, in the aftermath of Hurricane Katrina in 2005. However, for that event, the dermatopathology was not described as necropsies were not conducted. By contrast, the outbreaks in Australia occurred in areas where the resident dolphin population was well documented by long-term and ongoing field ecology and behavior studies with many known individuals; the waters inhabited by the dolphins were intensively monitored for physical and chemical parameters before, during and after the events; and when mortalities occurred, carcasses were retrieved in a timely manner for necropsy and sampling.

Based on these data, FWSD occurs when there is a sudden (days) and profound (>25ppt to <5ppt) decrease in salinity, that persists for weeks to months. The skin lesions appear initially as patchy pallor that progresses to raised targetoid areas of ulceration and colonization by variably colored mats of algae, diatoms, fungi and bacteria. Histologically, the early changes are cell swelling in the mid layer of the epidermis (hydropic change) that progresses to full depth ulceration or inflammation arising from the superficial dermis to create intra-epidermal pustules that erupt as ulcers. Death may ensue from fluid loss and electrolyte imbalance (Think severe third degree burns over most of the body surface). For some, resolution may occur depending on prevailing salinity or presumably intercurrent disease or individual immune status. In Australia, the outbreaks followed resumption of season rainfall following a prolonged drought that flooded the Gippsland Lakes (normally brackish to marine saline) with fresh water. In Western Australia, unusually high winter-spring rainfall in the river catchments similarly turned a normally marine/brackish habitat to freshwater. In the Gulf of Mexico, events have followed the heavy rainfall and storm surges in the aftermaths of Hurricanes Katrina and Harvey and as hurricane seasons become more severe as in 2020, these events are likely to increase in frequency. A common denominator is extreme weather events the like of which are on the rise with climate change and for that reason, we regard FWSD as an emerging disease of cetaceans in vulnerable coastal habitat. To read the paper in full please use this link: https://rdcu.be/ccfbl

Pádraig Duignan (TMMC, Sausalito, CA), Nahiid Stephens (Murdoch University, Western Australia) and Kate Robb (The Marine Mammal Foundation, Vic., Australia).

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