Previous studies suggest one or more elements may pose a threat to manatees and dugong health.1-8,10 This is not surprising given their proximity to humans and industrialized areas, and their migratory behavior. The aims of the present study were to determine whether: 1) elements are present in potentially harmful quantities in manatees; 2) element values differ with sex, age, or subspecies; 3) element values differ between geographical areas.
Whole blood and serum element concentrations from free-living, apparently healthy West Indian manatee subspecies, Trichechus manatus latirostris (n=20) and T. m. manatus (n=14), were measured and compared. The samples were collected from animals during routine health examinations in Florida and Belize, respectively. Blood samples were collected into contaminant free serum vacutainer tubes (BD Vacutainer, Sterile Interior, BD, Franklin Lakes, New Jersey, 07417-1885 USA) and heparinized (Li) vacutainer tubes (BD Vacutainer, Sterile Interior, BD, Franklin Lakes, New Jersey, 07417-1885 USA). Whole blood (n=32) and serum (n=35) levels of 29 elements were determined at the Utah State Veterinary Diagnostic Laboratory using plasma mass spectrometry. Element min-max ranges were compared with those listed for horses, cattle, and pigs.9 Statistical analysis using a linear model two-way ANOVA was used for minerals (As, Zn, Ni, Se and Mg) outside of the reference ranges used to evaluate potential physiologic differences. Relative ages were defined as "growing" (less than 250 cm in Belize; less than 275 cm in Florida) or "mature" (>250 cm in Belize; >275 cm in Florida). One-way ANOVA was then used to compare the two geographically-isolated populations of animals.
In comparison to terrestrial and other aquatic mammals the manatees had increased magnesium, zinc, and arsenic.9 There was no statistical difference between populations of manatees studied. Zinc values were significantly lower in juvenile animals when compared to adults. Only two suckling calves were sampled precluding statistical evaluation. However, it is interesting to note that these animals had the two lowest As and Zn values by greater than two standard deviations from the mean. Interestingly, a single animal in close proximity to a powerplant was evaluated, and did not have increased mercury blood concentrations.
In conclusion, this study describes 29 elemental blood values in two free-ranging subspecies of manatee prior to significant contamination due to petroleum exploration in the coastal waters around the state of Florida or possible disasters such as Hurricane Katrina. Given the federally endangered status of these animals, and the challenges of collecting tissue samples antemortem in field settings, whole blood and serum analysis of different elements provides a rapid, safe, and easy means of further assessing manatee health status.
Further toxicological evaluations in additional geographical locations, as well as in captive holding facilities, are encouraged. Sea grass and ascidian element analysis are currently being pursued as an underlying cause of increased blood concentration of As, Zn, and Mg.
We thank Nicole Auil (Wildlife Trust), Dr. Adrienne Atkins, and the capture teams in Belize and Florida for their help in manatee capture and data collection. We also thank the Florida Fish and Wildlife Conservation Commission and the Zoological Medicine Department at the College of Veterinary Medicine, University of Florida, for financial assistance. Lastly, we thank Karen Bischoff at Cornell University Veterinary Diagnostic Laboratory for consultation on this project. This work was done according to Sirenia permit #MA79172-4
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