Dynamics of caribou and wolves in northern British Columbia

Abstract

Major fluctuations in caribou (Rangifer tarandus) numbers have occurred since the settlement of European man in British Columbia. Caribou declined in the late 1930's and 1940's after moose (Alces alces) expanded their range and wolves (Canis lupus) increased. Following a wolf reduction program from 1949 to 1962, the caribou expanded until a high was reached in the late 1960's, after which the herds again diminished as wolf numbers increased and calf recruitment decreased. Three caribou populations were censused between 1976 and 1982, and an experiment was conducted on one of these areas (with the others as controls) to test the effect of wolf numbers on herd growth. The Spatsizi–Lawyers and Level–Kawdy populations inhabited ranges where wolf densities were near 9–10wolves/1000 km2;Spatsizi–Lawyers declined between 1977 and 1982(r = −0.13) and Level–Kawdy declined between 1977 and 1982(r = −0.12). We reduced wolves at the experimental Horseranch population from 10 to 1–4/1000 km2 and these caibou increased from 1977 to 1982 at an average exponential rate of 6% per year. None of the populations were heavily hunted; however, both declining populations had low calf survival with a mean of 55% of the calves dying within the first 2 weeks of life. Calf survival increased significantly at the Horseranch in the 3 years that wolves were reduced. In conclusion, we believe that the Spatsizi–Lawyers and Level–Kawdy populations declined as a result of predation on calves and adults. Yet, if wolves are managed to provide stabilizing recruitments for caribou, it should be possible to dampen the natural fluctuations of caribou and wolves that are frequent in unperturbed systems and maintain higher numbers of both species.