Hematological differences in Barents and Kara Seas polar bears (Ursus maritimus): what factors matter?

The Barents–Kara region is significantly affected by climate change, leading to the rapid degradation of habitats and the infiltration of new potential infectious agents dangerous to pagophilic species, particularly the polar bear (Ursus maritimus). For individuals captured in the Barents Sea and the Kara Sea in 2018–2021, the physiological status was monitored using hematological parameters and a body condition index, considering factors such as age, sex, reproductive status of females, and habitat type. No sex differences were found in blood characteristics, however, the total number of erythrocytes, leukocytes and neutrophils in cubs and juveniles was higher than in subadults and adults. The total number of leukocytes, lymphocytes, neutrophils, eosinophils, and the body condition index depended on the reproductive status of females. Additionally, a significant increase in the number of leukocytes, lymphocytes, and eosinophils, as well as the body condition index was observed in bears that foraged for food in the landfill near Belushya Guba (the Novaya Zemlya archipelago). Our results demonstrate the importance of including both individual characteristics and environmental conditions for assessing the health of polar bears.