Changes in survival rates and population dynamics of greater snow geese over a 30-year period: implications for hunting regulations
Gilles Gauthier, Département de Biologie, Université Laval, Sainte-Foy, PQ, G1K 7P4, Canada (fax 418 656 2043; e-mail email@example.com).
- 1In recent decades, the populations of several goose species have increased dramatically and are severely impacting on their habitat. We examined the relative contribution of reproduction and mortality to changes in the dynamics of the entire North American population of greater snow geese Anser caerulescens atlanticus from 1970 to 1998.
- 2The total population increased 10-fold over this period, with two phases of rapid population growth in 1970–74 and 1984–98 separated by an intervening period of stagnation. The reproductive rate was estimated from age ratios in the autumn, survival from ring recoveries, and harvest rates from hunter surveys.
- 3Variations in population growth could not be explained by changes in reproduction, which was similar across the three periods (overall mean 26 ± 3% young in the autumn flock) with no evidence of density-dependence.
- 4Adult survival did not differ between the two periods of rapid population growth (0·84 ± 0·04 during 1970–74 vs. 0·80 ± 0·04 during 1990–96), thus providing no evidence of density-dependence effects either. The survival rates of young could only be estimated during 1990–96, when they varied greatly (mean 0·36 ± 0·12, annual range 0·11–0·48).
- 5Adult harvest rates were much higher during the period of no population growth (0·11 ± 0·01%) than before (0·04 ± 0·01%) or after (0·06 ± 0·01%). The increased harvest starting in 1975 was due to the re-opening of the US hunting season. Thus, reduced survival due to increased hunting mortality apparently caused the stagnation of growth between 1975 and 1983.
- 6We conclude that hunting mortality has had the most impact on recent population dynamics in the greater snow goose and, in the absence of density-dependent effects, hunting could be used to limit the growth of this population.