MOOSE ON KALGIN ISLAND: ARE DENSITY-DEPENDENT PROCESSES RELATED TO HARVEST?

Abstract

We studied the demography of a population of Alaskan moose (Alces alces gigas) that was closed to immigration or emigration of Kalgin Island, Alaska, USA, from 1980 to 1987. This island population experienced neither severe weather nor predation from large mammalian carnivores. Effort and success by hunters was monitored carefully, and the age structure from harvested moose was used to estimate population size during each year. Moose were harvested heavily during permit hunts to reduce the population that had overshot  carrying capacity. The estimated population declined from 212 to 8 moose between 1982 and 1986. Harvest was linearly related to population size, but moose killed per unit of hunter effort (CPUE) exhibited a disparate pattern with hunter success initially declining with population size but then increasing dramatically at lower population sizes of moose. The overall age structure of moose became younger as harvest reduced the size of the population. The percentage of moose 3.5 – 5.5, and 6.5 – 12.5 years old declined with population size, whereas 0.5 year-old moose increased as the population declined. Recruitment of yearlings into the population on Kalgin Island exhibited a strong density-dependent response. Our analysis indicated an extremely high intrinsic rate of increase (r = 0.35 - 0.44) for those moose. Even with that high productivity, moose on Kalgin Island could not withstand the heavy harvest to which they were subjected, which exceeded maximum sustained yield during the early years to meet initial management objectives. Moose on Kalgin Island exhibited a strong density-dependent response to harvest, and we hypothesize that density-dependent mechanisms interact with harvest, predation, and severe weather to influence other populations of moose in Alaska.