External Effects of Mitigating Measures to Reduce Large Carnivore Predation on Sheep

Outfield range pastures with widely dispersed sheep are quite common in Norway, with a summer population of approximately 2.4 million animals. In many areas losses to predators are considerable and identifying efficient mitigating measures against predation is a prime target in nature management. In order to assess economic efficiency, any actual effect of the measure on predation and loss regime must be addressed. One problem with some research is the "scale problem". While sheep outfield home range areas have been measured from 2.2 - 33.8 km2, large carnivores on their ranges might use from several hundred up to even thousands of square kilometres. For lynx (Lynx lynx) the home range varies between 158 and 433 km2, wolverine (Gulo gulo) between 61 and 970 km2 and for the brown bear (Ursus arctos) from 171 to 33,041 km2. Thus there emerges a form of statistical dependence, since the exposure of the carnivores to actions and measures in a sheep home range or sample area might influence how the same carnivores behave outside the area. The external effects on society, the environment or other farmers may therefore outweigh advantages to farmers introducing the measure, and scale evaluation might be of crucial importance in designing field research projects exploring such measures.