Abstract 311 – Death and all its friends: mortality-based monitoring of health status in Croatian part of Dinaric-Pindos brown bear population

Djuro Huber, Nikica Prvanović Babić, Doroteja Huber, Ewa Serwa, Joanna Macur,
Łukasz Paśko, Jerzy Wiater, Lana Pađen, Maja Lazarus, Bartosz Leszczyński, Slaven Reljić,
Agnieszka Sergiel

Free-living wildlife, including bears, in most cases go through disease and eventually die
without it being directly observed. Only the most obvious cases e.g., human-induced death
(hunting, traffic kills) are recorded. However, the bodies of dead animals may reveal a wide
spectrum of pathologies at different stages, and its careful examination might give an
important insight into population health status. We conducted a limited but intensive survey of
72 human-induced brown bear mortalities in Croatia from 2021 through 2023. Most of
mortalities (67) were the result of hunting, and the remaining five individuals were traffic-killed.
Each bear was measured, aged and necropsied. Most organs were inspected on site and
multiple samples taken for further laboratory analyses, including on fatty acids, trace elements,
stress and reproductive hormones concentration in tissues, and histopathology. Reproductive
organs were also examined for its activity and eventual pathologies. One case of bilateral
polycystic ovary syndrome was recorded (out of 24 females in the sampled cohort). The
histological analysis of stomach walls revealed gastritis at various stages (from mild to
moderate chronic) in nine of 24 samples analysed. In one individual (of nine analysed) we
recorded severe fibrosis of left ventricle affecting 40% of myocardium and extending into the
heart muscle, and multifocal, moderate areas of cartilage metaplasia. Additionally, in case of
three individuals, mild myocardial fibrosis was found. The adrenal glands exhibited unilateral
cortical micronodules in case of nine individuals (out of 71 examined) that is 12,67% of bears
under study. All these examples illustrate the importance of mortality surveys, the information
load they carry on population health and warn about short-term and long-term threats. We
also propose that consistent, systematic, and extensive monitoring of mortalities additionally
facilitates surveying of contaminants and diseases.