Mortality in free-ranging Eurasian brown bears (Ursus arctos arctos) in Spain '1998-2018'

Abstract

Background: This work summarizes the mortality cases of twenty-five free-ranging Eurasian wild brown bears (Ursus arctos arctos) from the Cantabrian mountain range submitted for necropsy in Asturias and Castilla y León (northwestern Spain) from ' 1998 to 2018'. Results: Causes of death were classified both caused by (i) "human intervention" or "natural causes" and based on (ii) "infectious" or "non-infectious" etiology. In four cases (16%) it was not possible to determine the cause of death due to the inadequate preservation of collected specimens or insufficient tissue availability. Based on "human intervention" or "natural causes", seven out of the 21 (33.3%) brown bears in which the cause of death could be determined died as a consequence of "human intervention" due to illegal hunting (shooting or snare), handling or strychnine poisoning. In contrast, fourteen (66.7%) brown bears died by "natural causes" due to traumatic lesions (fights, unknown traumas or infanticide), infectious canine hepatitis, neoplasia, or mushroom poisoning. Based on "infectious" or "non-infectious" etiology nine out of the 21 (42.9%) brown bears died due to "infectious diseases", namely gangrenous myositis, infectious canine hepatitis or septicemia. The remaining twelve (57.1%) animals died due to "non-infectious" causes, which included handling, traumatic lesions such as shooting, snare, fighting or infanticide, strychnine poisoning, mushroom poisoning or neoplasia. In six of those cases traumatic lesions caused by human activities or by natural causes were complicated with bacterial infection (clostridiosis and septicemia) which finally caused the death of those animals. Additionally, exertional myopathy was observed in the handled animal and in one bear found in a snare. Conclusions: In a non-hunted population of Eurasian brown bear from the Cantabrian mountain range, main cause of death is attributed to “natural causes” mostly due to traumatic lesions and infectious diseases (primary developed such as infectious canine hepatitis or secondary developed such as clostridiosis or septicemia) which is in contrast to previously reported data for other bear populations.These data are valuable and may help in the conservation and management of this recovering population.