Abstract

Three atypical stranding events occurred in Virginia, USA between 2017–2021. During the month of November in 2017, 2018, and 2021, Virginia Aquarium’s Stranding Response Program responded to 14, 10, and 8 loggerhead sea turtles (Caretta caretta) over a period of 18, 6, and 11 days respectively (Live: 10, 9, 6. Fresh dead: 4, 1, 2). These events are considered atypical with near-surface water temperatures in the stranding region above threshold temperatures generally considered for cold-stun loggerheads in the NE (50–54°F).¹ Regional buoy temperatures indicated a warmer initial temperature mid-October (72–73°F) when loggerheads begin fall migration out of Chesapeake Bay (67–68°F).² This was followed by a greater negative slope (range of 10–20°F decrease) during the event periods, compared to regional data and non-event years (2019 and 2020, 66–67°F initial temperatures, range of 3–5°F decrease).² The size and species of turtles impacted during these events are also considered atypical as all were juvenile to sub-adult loggerheads and ranged in size from 19.4–110kg. In both 2018 and 2021, much smaller green and Kemp’s ridley sea turtles did not strand as cold-stuns in the region until 3–4 weeks after these atypical events with larger loggerheads.

The clinical presentation of the loggerheads that survived >12 hours are consistent with other reports of cold-stun syndrome in sea turtles.^1,3 All were severely lethargic to obtunded with marked to severe cardiorespiratory depression and ranged from normoglycemic to hyperglycemic. Respiratory or mixed acidosis (or indication of compensation) is commonly reported in the literature and is often seen in cold-stunned turtles in VA but was absent in all but one of these event turtles.^1,3 A predominate presenting condition was moderate to severe hypokalemia with normal to slightly elevated pH. Additionally, moderate to severe pneumonia was seen for most turtles on radiographs taken within 2–3 days of admission into rehab. Although pneumonia is a common sequala of cold-stunning, there is often a delay in development and/or radiograph change.⁴ Evidence of pneumonia, without overt aspiration pattern, present at time of admission may indicate respiratory infection or compromise of a longer chronicity than expected in an acute cold-stunning event. Body condition assessment via mean BCI (Fulton’s K index) at 1.38 ± 0.10 SD, was significantly lower (T=-6.592, df=57.109, p-value <0.001) when compared with regional fresh dead or live stranded loggerheads of non-disease etiology (1.578 ± 0.17 SD).⁵ The poor body condition and nutritional status is unexpected for loggerheads after foraging in the Chesapeake Bay for the summer and early fall.

The warmer initial temperatures during these events may have impacted the cues to begin migration out of the Bay. However, a degree of systemic, respiratory and or immune compromise is suspected with the lower mean BCI and chronicity of respiratory disease seen in these turtles at time of stranding. While etiology is unknown, a compromised state would make these turtles more sensitive to the water temperature changes despite their larger size and more susceptible to cold-stunning earlier in the season than other turtles that are likely still in the region.

Acknowledgements

The authors wish to thank Virginia Aquarium’s Stranding Response Program staff and volunteers for their work in stranding response, sea turtle rehabilitation, and for their contributions to this study.

Literature Cited

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2.  Mansfield KL, Saba VS, Keinath JA, Musick JA. 2009. Satellite tracking reveals a dichotomy in migrating strategies among juvenile loggerhead turtles in the Northwest Atlantic. Mar Biol Biology 156: 2555–2570.

3.  Innis CJ, McGowan JP, Burgess EA. 2019. Cold-stunned Loggerhead Sea Turtles (Caretta caretta): Initial vs. Convalescent Physiologic Status and Physiologic Findings Associated with Death. J Herpetol Med Surg 29:105–112.

4.  Stockman J, Innis CJ, Solano M, Brisson JO, Kass PH, Tlusty MF, Weber ES. 2013. Prevalence, distribution, and progression of radiographic abnormalities in the lungs of cold-stunned Kemp’s ridley sea turtles (Lepidochelys kempii): 89 cases (2002–2005). J Am Vet Med Assoc 242:675–681.

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