Abstract

Body condition evaluation in free-ranging wildlife provides an important index for health assessment, foraging success, and reproductive success. Ultrasonography has been used to measure subcutaneous fat depth as an indicator of body condition in many species but has not been applied in sea turtles. In marine mammals, ultrasonography has been used to document dynamic seasonal changes in blubber depth and regional patterns of blubber deposition and mobilization.^1-3 Leatherback turtles (Dermochelys coriacea) are ideal candidates among sea turtles to explore the use of ultrasonography due to their highly developed peripheral fat layers which allow them to forage in temperate waters.^4,5 Seasonal deposition and mobilization of fat stores result in substantial cyclical changes in body condition characterized by extreme alterations in body mass, carapace shape, prominence of dorsal ridges, and thickness of the neck and base of extremities.^6,7 To assess the efficacy of this technique for leatherback turtles, ultrasonography was performed on a total of 36 turtles: live foraging subadults and adults captured in water from central California (n = 9) and Nova Scotia (n = 3); live nesting adult females from Florida (n = 16); dead stranded adults from California (n = 2), Massachusetts (n = 1), and Nova Scotia (n = 2); and dead immatures recovered as fisheries bycatch from the Pacific Islands region (n = 3). Ultrasound images were obtained from four anatomical sites: left shoulder, left neck, dorsal neck, and dorsal base of the left hind flipper. Ultrasound sites were chosen based upon previously identified regions of fat deposition, accessibility of the site during nesting and on a capture boat, and ability of the ultrasound signal to penetrate the tissue. Ultrasound measurements were validated through direct measurement via surgical biopsy or necropsy and confirmed histologically in a subset of turtles. Linear regression was used to compare total depth values from both methods and demonstrated good correlation between ultrasound and direct measurements (r² = 0.74, p = 0.001). The dorsal shoulder region was the optimal site for differentiation of tissue layers and appeared less affected by body position or animal movement as compared with the neck and hind end. Potential issues with this method include avoidance of excessive manual pressure, maintaining the front flipper in a neutral (45–90 degree) position, tissue contracture from previous injury to the site, and possible freeze-thaw artifact. Portable ultrasound can be used to rapidly assess leatherback turtle body condition in the field with minimal manual restraint during nesting and in-water capture operations. Quantitative assessment of body condition may be used in conjunction with morphometric data, clinical health parameters, and contaminant exposure data to facilitate health comparisons between increasing and declining leatherback populations.

Acknowledgements

This project was supported in part by the California Department of Fish and Wildlife's Oil Spill Response Trust Fund through the Oiled Wildlife Care Network at the Karen C. Drayer Wildlife Health Center, School of Veterinary Medicine, University of California, Davis. The authors thank the in-water capture and aerial teams from NOAA Southwest Fisheries Science Center and Canadian Sea Turtle Network; the necropsy teams from the California Department of Fish and Wildlife's Marine Wildlife Veterinary Care and Research Center, Atlantic Veterinary College, and NOAA Pacific Islands Fisheries Science Center; C. Innis, J. Cavin, and the New England Aquarium Departments of Animal Health and Rescue and Rehabilitation; the leatherback field research team from the Loggerhead Marinelife Center; marine wildlife stranding networks in the United States and Canada; and the NOAA Pacific Islands longline fisheries observer program.

* Presenting author

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