Abstract
Blood analytes are a critical tool in evaluating the general health status of cetacean populations, so it is important to understand the intrinsic variability of hematology and blood chemistry values.1 Previous studies have reported data for follow-up periods of several years in captive and wild populations,2 but studies over long periods of time (> 20 years) have not been reported. This long-term dataset followed 34 captive belugas from three facility locations for up to 22 years. The main objectives of this study were to characterize the long-term trajectories and variation of hematology and serum chemistry analyte values in apparently healthy captive beluga whales (Delphinapterus leucas), to quantify variation between animals, and to examine influences of biology and environment on variation, using analytical techniques for monitoring of clinical blood values that may be applied to wild populations of marine mammals that are amenable to repeated captures for health assessments and blood sampling. A series of linear mixed effects models3 was used to describe trajectories and assess the relationship between the analytes and sex, age, season, facility location, and ambient air temperature.4,5 Individual whales showed both consistent differences from each other and variation within whale over time. Most analytes showed significant differences in mean levels between males and females and changes with age. Seasonal variation was observed for hemoglobin, hematocrit, mean corpuscular volume (MCV), monocytes, alkaline phosphatase, total bilirubin, cholesterol and triglycerides. Circannual variation patterns were similar across facilities for MCV, white blood cells, creatinine, globulin, creatinine phosphokinase, phosphorus, sodium, and chloride. Facility location was associated with the largest effects on analyte levels for both hematology and serum chemistry relative to the other covariates, while age, sex and ambient temperature had lower effects on analyte levels compared to those of facility location and season. These findings from a long-term assessment of individual variation in healthy cetaceans agree with previous reports that many blood analytes differ significantly between age groups and seasons and provide important baseline information to assist in future health monitoring efforts.6,7 Variability from factors such as sex, age, season, and nutritional status, as well as individual tendencies to track high or low, should be considered when interpreting blood analyte values and animal health in both captive and wild populations over time.
Acknowledgments
The authors thank the Sea World's clinical veterinary and laboratory staff for sample collection, analysis, and tabulation of these extensive data.
References
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