Harvest restrictions fail to influence population abundance

Abstract

Evaluating changes in population abundance is essential to assess the efficacy of conservation actions. Antler point restrictions are a high-profile regulatory action aimed to advance male age structure in cervid populations, but there is a limited understanding of how restrictions affect population size and structure. Our study evaluated population-level effects of an antler point restriction on white-tailed deer (Odocoileus virginianus) abundance and sex and age composition using a before–after control–impact design. Antler point restrictions are intended to increase the abundance of legal-antlered deer, but the impact on the abundance of antlerless deer is less known. By limiting the harvest of yearling males, antler point restrictions may lead hunters to shift harvest toward antlerless deer, potentially increasing female mortality and reducing population fecundity. We conducted camera-trap surveys of deer in zones with and without antler point restrictions before and 3 years after the implementation of restrictions and used N-mixture models to estimate annual abundance by sex and age class. The restriction prohibited the harvest of antlered deer with fewer than four points on a single antler beam (i.e., on one side). Our results suggest that the restrictions did not influence population abundance of deer. The abundance of legal-antlered deer increased in both the restriction zone and the non-restriction zone (opposing predictions), as did the abundance of females, sublegal-antlered deer, and fawns (opposing predictions). Partial controllability, or a failure of the regulation to influence realized harvest, likely explains these results, since antlerless deer harvest did not change throughout the duration of our study while slight but insignificant changes in antlered harvest were observed in the restriction zone. Our results highlight potential limitations of antler point restrictions achieving desired effects for population reduction goals and the importance of independently evaluating conservation and management actions.