Upwell’s Wildlife Veterinarian, Dr. Heather Harris, shares her innovative approach to measure the health of leatherback sea turtles during her recent field study in Florida. Dr. Harris’ work is part of Upwell's new ecosystem health program. The aim of this program is to better understand specific environmental threats that present health risks to sea turtles and to demonstrate to the wider public how sea turtles act as sentinels for the health of our oceans. Dr. Harris has a DVM in Veterinary Medicine and MPVM in Wildlife Disease Ecology from the University of California, Davis. She is a diplomate of the American College of Veterinary Preventive Medicine.
How do you weigh an adult leatherback sea turtle often likened to the size of a Volkswagen Bug?! On foraging grounds off the coast of California, where leatherbacks are greedily feasting on jellies (eating up to a quarter of their body weight per day), they grow enormously round and bulky, their necks and hips literally bulging with fat rolls. The development of this fatty blubber layer provides energy and insulation that allows these marine reptiles to thrive in cold temperate water, unlike their hard-shelled cousins. I like to think of them as a sort of hybrid creature, somewhere between a sea turtle and an elephant seal! In stark contrast, after many months of fasting and migrating to tropical nesting beaches, these same turtles can appear quite thin, their necks sagging and concave, hip bones jutting out, and the spiny ridges of the carapace forming prominent peaks.
How can we accurately quantify these changes? And what can this tell us about sea turtle health? To address these questions, we are applying the tools of veterinary medicine to evaluate the health and body condition of this critically endangered species. Back in 2011, I collaborated with a group of scientists including partners from the Loggerhead Marinelife Center in Juno Beach, Florida to validate a novel technique that uses ultrasonography to non-invasively measure fat depth in leatherback turtles (Harris et al., 2016). The next phase involves sampling turtles at the extremes of body condition to quantify these differences. This includes subjectively scoring their body condition using a descriptive scale that ranks individuals from 1 (emaciated) to 5 (obese), which often involves conversations about how “girthy” or “ridgey” they look. We also obtain body weights, take standard measurements of the carapace and neck, determine the fat depth with ultrasound, and analyze blood to evaluate the best predictors of body condition. I have sampled numerous foraging leatherbacks captured at sea in California with the NOAA Marine Turtle Ecology and Assessment Program for this study, including weighing them on a rocking boat suspended from an A-frame with a winch system. Last week, Upwell’s Executive Director, Dr. George Shillinger, and I had the opportunity to travel back to Juno Beach to work with the fantastic team at the Loggerhead Marinelife Center under the Director of Research, Dr. Justin Perrault. We were joined by my colleague from Cal Poly, Dr. Heather Liwanag, who generously loaned us her carbon fiber tripod and scale (which she actually uses to weigh elephant seals on the beach in California!).
Our team successfully weighed six adult female leatherbacks and collected data and blood samples from a total of nine animals. To our knowledge, these are the first body weights obtained from nesting leatherbacks in the contiguous United States. Our protocol was adapted from methods used by sea turtle colleagues in other parts of the world. We conducted nightly beach surveys by ATV, scanning the beach intently for characteristic large tracks and enormous dark shapes at the water’s edge. Once a leatherback emerged from the water, we waited from a safe distance for her to choose a nesting spot, form a body pit, and dig a deep nest chamber with her hind flippers in the wet sand. Once she began laying her eggs, we had approximately 10-minutes to complete our sampling without disrupting her natural nesting behavior. I performed ultrasound while others carefully took measurements, collected a blood sample, and checked tags by the red-filtered light of our headlamps. We positioned the tripod over the turtle and dug a channel in the sand under her body to place thick straps to support her weight. When she had finished laying the clutch and started to cover her nest, we connected the straps to the scale and gently raised her up using a manual hoist system. None of the turtles showed any response to the weighing process and once lowered to the sand immediately returned to covering and disguising their nests before heading back to the ocean.
The Atlantic leatherbacks we studied in Florida can serve as an indicator of ocean health. The ability to identify biomarkers for body condition has key implications for predicting individual and population health of leatherback sea turtles. We also plan to use the data gathered to facilitate health comparisons between the critically endangered and declining Pacific leatherback population and the more stable Atlantic population to identify health threats and contribute to their conservation and recovery.
A huge thank you from Upwell to our partners at the Loggerhead Marinelife Center for supporting this research collaboration!
Disclaimer: All marine turtle images taken in Florida were obtained with the approval of the U.S. Fish & Wildlife Service (USFWS) and the Florida Fish & Wildlife Conservation Commission (FWC) under conditions not harmful to this or other turtles. Images were acquired while conducting authorized research activities pursuant to FWC MTP-19-205.