Evaluating measures of hunting effort in a bushmeat system

The negative impact of bushmeat hunting on prey species has been frequently claimed, but little thought has been given to how the level of hunting should most appropriately be measured. Current methods range from qualitative descriptions to quantified measures, and in many cases these are used to infer the biological impact of hunting, when they are in fact economic measures of the effort invested by a hunter. The choice of measure used has important implications for correctly attributing observed levels of prey abundance to a particular level of hunting, and for the use of hunting statistic data as an index of abundance. Using information from over 200 hunter follows and eight hunting camp diaries collected over a 15 month period in Equatorial Guinea, we investigate how hunting effort is most appropriately measured. We explore the use of time as a measure of effort, the effect of hunting method and compare hunter and prey perspectives of catch, in order to investigate the possible sources of bias associated with different measures. We show (1) that total time measures can be biased, overestimating biologically relevant effort; (2) that quantifying trapping effort is problematic due to variable trap checking rates, variable trap group composition and species trap specificity; and (3) that economically relevant measures of catch, taken from the hunter perspective underestimate the true biological impact of hunting. To our knowledge this is the first study to investigate and explicitly quantify the sources of bias that exist between different hunting effort measures. Our results have important implications for how future studies should measure hunting effort in order to assess properly the biological impact of bushmeat hunting, but further comparative studies are needed to investigate the existence of biased effort measures in a range of hunting systems.