Predicting hunting success on willow ptarmigan using bag statistics and distance sampling estimates

Abstract

Willow ptarmigan is a popular game species for recreational hunting purpose throughout its range and long term harvest statistics are available for many areas. For the State owned land in Sweden hunting report rates are unusually high and provide a high level of information, including hunting effort, making this a unique dataset. In easy accessible hunting areas hunting pressure commonly is high, making monitoring and managing populations necessary. During this study harvest data from all hunting areas within the County of Jämtland and population estimates from four long term monitoring areas from the County of Jämtland, Sweden, from 1996 – 2010 were analysed. The aim of this study was to develop methods to predict the success of hunters based on previous years harvest data and results from the yearly ptarmigan counts prior to the start of the hunting season, to avoid over-harvesting. Further a method to calculate the amount of hunting possible to achieve a defined harvest level was developed. And last, a set of management options to reduce hunting pressure were assessed. Adult density, proportion of successfully reproducing adults and average brood size explained most of the variance within bag size (R2adj. = 0.72). CPUE did not differ over time (p=0.12) and area (p=0.12) and allowed to calculate amount of hunting possible to achieve certain harvest rate. Observed amount of hunting was lower than the hunting limit in most cases. Excluding foreign hunters can reduce total harvest up to 40% (2008/2009) while reducing bag limit and shortening the hunting season will have a marginal effect on harvest. . I suggest using adult density, proportion of successfully reproducing adults and average brood size to determine harvest levels rather than overall density. Calculating hunting levels should be done by using a fixed CPUE value which takes local fluctuations into account and allows a certain amount of hunting every year. I suggest that the reporting system for hunting results is revised so the effective amount of hunting can be calculated and used for management decisions.