Legal hunting is causing demographic changes to brown bear populations in Sweden, altering vital rates such as numbers of surviving offspring and life expectancy. The findings, published online in Nature Ecology & Evolution, are the culmination of 30 years of data from tracking individual bears.
Protection and sustainable management has led to brown bear numbers in northern and central Europe slowly increasing from a state of near eradication at the start of the twentieth century. However, Richard Bischof and colleagues now suggest that hunting takes a toll that is more complex than just numbers.
By monitoring bears in southern Sweden since 1985, the researchers show that hunting alters the standard course of bear life-history. For example, although young bears are protected while they accompany their mother, hunting becomes the leading source of death among bears aged over three years, which counters the natural pattern of reduced mortality in adults compared to juveniles. The authors find that life expectancy of one-year-old bears was 8.8 years during years with low hunting pressure, but only 5.2 years when hunting pressure was at its highest. They also find that female bears’ reproductive value - the future number of female offspring - decreased during periods of high hunting pressure.
The authors conclude that these changes to bear demographics, combined with climatic changes that alter the exposure of the bears to hunting, must be considered to make hunting regulation more appropriate for long-term management.