Is Lachrymal Fluid a Potential Method for Cortisol Measurement in Wild Harbor Seals?: A Pilot Study

Abstract

Despite stable population size in harbor seals anthropogenic interferences in the marine environment still represent a highly discussed matter within research. In order to quantify and evaluate assumed stressful events in the marine environment, there is a permanent search for new methods and materials for the evaluation of stress. Previous studies are often based on venipuncture and determination of the classic “stress-related hormones” in blood, showing the change of activity of the hypothalamic pituitary adrenocortical (HPA) axis as well as the sympathetic adrenomedullary system. Though blood sampling represents the gold-standard, it is influenced by disturbance of sampling, representing an invasive stressful method itself. Therefore, new non–invasive approaches have to be developed to determine HPA modifications as well as other matrices to reduce stress caused by handling and trapping. In addition to saliva and blood, the present study tested cortisol measurement in lachrymal fluid as a possible method for rapid stress evaluation. Therefore, 17 harbor seals (13 male, four female) were examined during a health monitoring program in April 2013. Lachrymal fluid was collected using a swab which was carefully inserted into the conjunctival sack. For comparison, serum and saliva were also sampled afterwards. Cortisol was detected in lachrymal fluid, saliva and blood of all investigated animals. Evaluation of regression analysis showed a good correlation (R2 = 0.82) between serum cortisol and “free” cortisol in lachrymal fluid. This study showed for the first time the possibility of lachrymal fluid sampling as a non-invasive method to asses stress in harbor seals.