Research - Health assessments
The relationship between turtle weight (y-axis) and shell length (x-axis) among the three species of sea turtles captured by trawling in coastal waters off SC, GA, and northern FL. Fewer than a dozen green sea turtles (green triangles) have been captured by our various surveys since 2000, all of which have been very small juveniles. Kemp’s ridley (red square) and loggerhead sea turtles (gray circles) captured to date encompass small juvenile to large adult sizes, but predominantly consist of immature individuals.
Documenting the condition of sea turtles captured in coastal waters is equally as important as monitoring catch rates and demographic trends. All sea turtles receive an external physical examination while on board, during which time particular attention is paid to prevalence of epibiont load, body mass, scale and keratin integrity, and unusual growths or injuries. Overall, sea turtles captured in our surveys since 2000 appear to be in good health. Outwardly, only about 3% appear emaciated or exhibit heavy barnacle loads often associated with emaciation. About 10% of sea turtles are described as rotund, with visibly convex plastrons and thick mass. Keratin and/or scale shedding is common, but rarely affects more than 15% of a body part. Growths and lesions are rare; however, evidence of physical injury is present in one of every four sea turtles captured.
Injuries range from minor abrasions to severe lacerations and amputations; however, nearly 90% of these injuries were fully healed at the time of capture [26]. Injuries have been recorded for all regions of the body, but most often afflict the carapace and flippers. Injured sea turtles are captured throughout the study area, but occur with significantly greater frequency near major ports. These observations collectively substantiate the resiliency of loggerhead sea turtles to sub-lethal injuries as well as identify geographic areas of greatest potential where loggerheads may become injured.
An adult female loggerhead with a healed shark bite wound on the rear portion of the right side of her carapace (shell). Because of the healed nature of this wound it is not possible to determine when the injury occurred, but given the prevalence of such wounds it is clear that turtles face a variety of threats at sea which are not always lethal.
Standard clinical blood values also substantiate the suggestion of a healthy population of sea turtles captured by trawling in the various surveys associated with this research since 2000. Red blood cell counts for loggerhead sea turtles were only deemed low (<30% of blood volume) for 1% (19) of individuals, which among other causes could indicate parasites. High (>44) red blood cell counts, a potential indication of dehydration, were only noted in 2% (28) of loggerhead sea turtles. Similar total protein levels were observed among loggerhead sea turtles with red blood cell counts <20% (total protein = 1 to 5.2 umol/dL, average = 2.7), red blood cell counts between 20% and 44% (total protein = 0.8 to 9.2 umol/dL, average = 4.7), and red blood cell counts >44% (total protein = 2.9 to 7.3 umol/dL, average = 4.7). Ninety percent of loggerhead sea turtles exhibited blood glucose values between 58 and 144 mg/dL, with only 1% each classified as hypoglycemic (<50 mg/dL) or hyperglycemic (>200 mg/dL).
Blood chemistry data analyzed by Antech Diagnostics (Memphis, TN) are available for a subset (454) of sea turtles provide additional insights. Data appear to be independent of turtle species, perceived health, collection location, and turtle size; however, relationships between blood parameters provide insight into sea turtle biology and health. A 76% similarity was noted between turtle size and total protein (predominantly globulin). An 80% similarity was noted between sodium and chloride levels. Blood urea nitrogen (BUN) was more closely aligned with blood glucose (73% similarity) than it was uric acid, which was most closely aligned (71% similarity) with Creatine Phosphokinase (CPK). Potassium levels were most closely aligned (69% similarity) with Aspartate Aminotransferase (AST).
The inter-relatedness between and influences on blood chemistry values, based on more than 450 samples. Species, size, geographic capture location, and outward physical appearance seem to exert little influence on blood chemistry values.
Red blood cell count distributions measured by the Antech Diagnostics laboratory were similar to values recorded at sea, with 95% of observations between 25 and 41% of blood volume. Ninety-five percent of white blood cell (WBC) counts ranged from 6 to 18 x 103 per microliter. Differences in WBC between perceived healthy and sick sea turtles were not detected, with the strongest relationship (lymphocytes and capture location) having only a 66% similarity. White blood cells were predominantly composed of lymphocytes (50%) and neutrophils (44%), followed by eosinophils (4%), basophils (1%), and monocytes (1%). These observations collectively suggest that sea turtles captured in various trawl surveys managed by the SCDNR MRD since 2000 are relatively healthy and/or that the analyses performed by Antech do not provide a sufficient level of resolution for discriminating between sick and healthy sea turtles.
Mercury, heavy metals, and perflourinated compounds have been examined for a subset of sea turtles captured since 2000 by a suite of collaborators. Mercury [27, 28] and heavy metals [29] appear to generally be stored in tissues or circulate in the blood at sub-lethal levels. Mercury concentration has been associated with geographic location (notably major industrial inlets [27]), but geographic location alone does not explain a large proportion of variability in mercury values among individual sea turtles. Mercury values are only weakly associated (63% similarity) with Antech blood chemistries and cell counts, although significant correlations have been reported between mercury and some Antech parameters [24]. In contrast, exposure to contaminants such as perflourinated compounds and organochlorines are strongly associated with turtle species, turtle size, and geographic location [30, 31, 32].
Since 2006, we have also partnered with numerous collaborators to conduct in depth assessments of sea turtle nutrition. Stable isotope concentrations have been evaluated for several tissues (blood, skin, and keratin) in juvenile and adult male loggerhead sea turtles. Stable isotopes correlate well with geographic region [33]; however, because it is unclear whether these correlations reflect a shift in foraging patterns or a shift in ambient food web signatures, geographic analysis of water samples and potential prey items is currently underway.
Vitamin, mineral, and lipid panels have also been completed in conjunction with several veterinary schools and rehabilitation facilities throughout the region. Preliminary nutritional data sets have been presented at several scientific symposia, and publication of final results is anticipated in the near future.
26 Alderson, J.E. 2009. Characterization of injuries and health of injured loggerhead sea turtles (Caretta caretta) in coastal waters of the southeastern U.S. Thesis, College of Charleston.
27 Day RD, Christopher SJ, Becker PR, Whitaker DW (2005) Monitoring mercury in the loggerhead sea turtle, Caretta caretta. Environ. Sci. Tech. 39(2):437-446.
28 Day RD, Segars AL, Arendt MD, Lee AM, Peden-Adams MM (2007) Relationship of blood mercury levels to health parameters in the loggerhead sea turtle (Caretta caretta). Environ. Health Perspect. 115:1421-1428.
29 Register, A.L. 2011. Effects of Heavy Metal Pollution on the Loggerhead Sea Turtle. Thesis, Loma Linda University.
30 Keller JM, Kannan K, Taniyasu S, Yamashita N, Day RD, Arendt MD, Segars AL, Kucklick JR. 2005. Perflourinated compounds in the plasma of loggerhead and Kemp’s ridley sea turtles from the southeastern coast of the United States. Enviorn Sci Technol 39:9101-9108.
31 O'Connell SG, Arendt M, Segars A, Kimmel T, Braun-McNeill J, Avens L, Schroeder B, Ngai L, Kucklick JR, Keller JM. 2010. Temporal and spatial trends of perfluorinatd compounds in juvenile loggerhead sea turtles (Caretta caretta) along the East Coast of the United States. Environ Sci Technol 44:5202–5209.
32 Ragland JM, Arendt MD, Kucklick JR, Keller JM. 2011. Persistent organic pollutants in blood plasma of satellite-tracked adult male loggerhead sea turtles (Caretta caretta). Env Tox Chem 30(7):1549-1556.
33 Pajuelo, M., K.A. Bjorndal, K.J. Reich, M.D. Arendt, and A.B. Bolten. 2012. Distribution of foraging habitats of male loggerhead turtles (Caretta caretta) as revealed by stable isotopes and satellite telemetry. Mar. Bio. 159(6):1255–1267.