The caribou herd that migrates through the Prudhoe Bay oil field has tripled since development began 20 years ago. Scientists attribute the 1978-1992 increase in the Central Arctic caribou herd's population to several factors. Oil drilling activities have driven away or killed the predators in the herd's calving ground. The Prudhoe Bay area is closed to hunting. Alaska Department of Fish and Game show that birth rates have actually declined over the last ten years.
Female caribou avoid industrial facilities when they are calving or accompanied by young calves.
Since 1992, there has been a noticeable decline in the size of the herd - from about 23,400 animals in 1992 to 18,000 in summer of 1995, accordingto the count released in late October by the Alaska Department of Fish and Game. Low calf production by undernourished cows is thought to be the cause for the 23 percent recent decline. The Department's report showed that the eastern portion of the herd, that stays farthese from the oil fields, was less affected by the decline. Polar bears are especially at risk if the coastal plain is developed. The plain contains the densest concentration of polar bear dens in the U.S. and 35 percent of all Beaufort Sea polar bear dens.