The Fortymile caribou herd: novel proposed management and relevant biology, 1992-1997

  • Rodney D. Boertje
  • Craig L. Gardner
Keywords: caribou, Fortymile, management, Alaska, condition, fertility control, mortality, nutrition, predation, pregnancy rate, translocation, sterilization


A diverse, international Fortymile Planning Team wrote a novel Fortymile caribou herd {Rangifer tarandus granti) Management Plan in 1995 (Boertje & Gardner, 1996: 56-77). The primary goal of this plan is to begin restoring the Fortymile herd to its former range; >70% of the herd's former range was abandoned as herd size declined. Specific objectives call for increasing the Fortymile herd by at least 5-10% annually from 1998-2002. We describe demographics of the herd, factors limiting the herd, and condition of the herd and range during 1992-1997. These data were useful in proposing management actions for the herd and should be instrumental in future evaluations of the plan's actions. The following points summarize herd biology relevant to management proposed by the Fortymile Planning Team: 1. Herd numbers remained relatively stable during 1990-1995 (about 22 000-23 000 caribou). On 21 June 1996 we counted about 900 additional caribou in the herd, probably a result of increased pregnancy rates in 1996. On 26 June 1997 we counted about 2500 additional caribou in the herd, probably a result of recruitment of the abundant 1996 calves and excellent early survival of the 1997 calves. The Team deemed that implementing management actions during a period of natural growth would be opportune. 2. Wolf (Canis lupus) and grizzly bear (Ursus arctos) predation were the most important sources of mortality, despite over a decade of the most liberal regulations in the state for harvesting of wolves and grizzly bears. Wolves were the most important predator. Wolves killed between 2000 and 3000 caribou calves annually during this study and between 1000 and 2300 older caribou; 1200-1900 calves were killed from May through September. No significant differences in annual wolf predation rates on calves or adults were observed between 1994 and early winter 1997. Reducing wolf predation was judged by the Team to be the most manageable way to help hasten or stimulate significant herd growth. To reduce wolf predation, the Team envisioned state-sponsored wolf translocations and fertility control in 15 key wolf packs during November 1997-May 2001. Also, wolf trappers were encouraged to shift their efforts to specific areas. 3. To increase social acceptance of the management plan, the Fortymile Team proposed reducing the annual caribou harvest to 150 bulls for 5 years beginning in 1996. Reducing annual harvests from 200-500 bulls (<2% of the herd, 1990-1995) to 150 bulls (<1% of the herd, 1996-2000) will not result in the desired 5-10% annual rates of herd increase. 4. We found consistent evidence for moderate to high nutritional status in the Fortymile herd when indices were compared with other Alaskan herds (Whitten et al, 1992; Valkenburg, 1997). The single evidence for malnutrition during 1992-1997 was the low pregnancy rate during 1993 following the abnormally short growing season of 1992. However, this low pregnancy rate resulted in no strong decline in Fortymile herd numbers, as occurred in the Delta and Denali herds (Boertje et al, 1996). No significant diseases were found among Fortymile caribou. 5. Winter range can support elevated caribou numbers both in regards to lichen availability on currently used winter range and the availability of vast expanses of winter range formerly used by the herd.
How to Cite
Boertje, R. D., & Gardner, C. L. (2000). The Fortymile caribou herd: novel proposed management and relevant biology, 1992-1997. Rangifer, 20(5), 17-37.