Cumulative impacts of an evolving oil-field complex on the distribution of calving caribou

Abstract

We investigated changes in distribution and terrain use of calving barren-ground caribou (Rangifer tarandus granti) with increasing density of roads in the Kuparuk Development Area, an oil-field region near Prudhoe Bay, Alaska. In June of 1987-1992, caribou density, as determined by aerial surveys, was inversely related to road density, declining by 63% at >0.0-0.3 km road/km2 and by 86% at >0.6-0.9 km road/km2. The latter road density virtually excluded cow-calf pairs. Effects of avoidance were most apparent in preferred rugged terrain, comprising important habitats for foraging during the calving period. Our results show that (i) females and calves are far more sensitive to surface development than adult males and yearlings, (ii) the greatest incremental impacts are attributable to initial construction of roads and related facilities, and (iii) the extent of avoidance greatly exceeds the physical "footprint" of an oil-field complex. A disproportionate reduction in use of foraging habitats within the Kuparuk Development Area, combined with decreasing tolerance of the expanding industrial complex, may explain the recent displacement of some calving activity to areas farther inland, and, in part, lower fecundity. Possible consequences include heightened competition for forage, increased risk of predation, and lower productivity of the herd.