Abstract

Bottlenose dolphins (Tursiops truncatus) have a worldwide distribution and often inhabit estuarine environments, indicating their ability to maintain homeostasis in low salinity for limited periods of time. Understanding the physiological changes and limits of low salinity and exposure duration is critical for dolphin conservation, as evidenced by multiple recent mortality events caused by significant decreases in environmental salinity, as well as increasing concern over anthropologically-driven salinity changes.

Stranding data has provided some knowledge about epidermal and biochemical changes associated with wild dolphins’ low salinity exposure; however, the exposure duration and salinity level are often unknown or estimated. A retrospective analysis of medical records from 46 managed dolphins in the U.S. Navy Marine Mammal Program and blood results from 43 Navy dolphins exposed to a variety of salinity levels during deployments for different durations covering 43 years (1967–2010) was performed to assess epidermal, biochemical and hormonal changes. Blood samples collected during low salinity exposure (0–30 parts per thousand; ppt) were compared to samples collected while the same dolphins were in seawater (31–35 ppt).

Epidermal changes were observed in 35% of dolphins in the low salinity exposure cohort, with the prevalence inversely proportional to the salinity level. Significant decreases in serum sodium, chloride, and calculated serum osmolality and significant increases in blood urea nitrogen and aldosterone were observed during low salinity exposure. An improved understanding of the homeostatic limits of exposure duration and salinity level in dolphins will allow for enhanced animal care and conservation management decisions during low salinity exposure events.

Acknowledgements

The authors would like to sincerely thank the U.S. Navy Marine Mammal Program for providing the highest standard of care to the Navy dolphins over the past 60 years and collecting valuable data that made this publication a reality.

Literature Cited

1.  McClain AM, Daniels R, Gomez FM, Ridgway SH, Takeshita R, Jensen ED, Smith CR. 2020. Physiological effects of low salinity exposure on bottlenose dolphins (Tursiops truncatus). J. Zool. Bot. Gard. 1, 61–75.