Research Handling Effects on Stress Hormones, Blood Parameters, and Heart Rate in Juvenile Northern Elephant Seals (Mirounga angustirostris)

Wildlife researchers must balance the need to safely capture and handle their study animals to sample tissues, collect morphological measurements, and attach dataloggers while simultaneously ensuring their results are not confounded by stress artifacts caused by handling. To determine the physiological effects of research activities including chemical immobilization, transport, instrumentation with biologgers, and overnight holding on a model marine mammal species, I collected hormone, blood chemistry, hematology, and heart rate data from 19 juvenile northern elephant seals (Mirounga angustirostris) throughout a translocation experiment. Across my six sampling timepoints, cortisol and aldosterone data revealed a moderate hormonal stress response to handling that was accompanied by minor changes in hematocrit, blood glucose, and blood lactate, but not ketone bodies or erythrocyte sedimentation rate. I also performed the first assessment of heart rate as a stress indicator in this species and found that mean heart rate, interbeat interval range, and apnea-eupnea cycles were influenced by handling. However, by the time seals were recaptured after several days at sea, all hormonal and hematological parameters had returned to baseline levels and 95% of study animals were resighted in the wild up to two years post-translocation. Together these findings suggest that while northern elephant seals exhibit mild physiological stress responses to handling activities in the short term, they recover rapidly and show no long-term deleterious effects, making them a robust species for ecological and physiological research