Interpreting long-term trends in bushmeat harvest in southeast Cameroon

Measuring hunting sustainability across West/Central African forests remains a challenge. Long-term assessment of trends is crucial. Via hunter-reported surveys we collected offtake data in three villages near the Dja Biosphere Reserve (southeast Cameroon). During four months (March–June) in 2003, 2009 and 2016, we gathered information on hunters, prey species and number of carcasses brought to the three settlements. Because it was not possible to record hunter effort i.e. the time a hunter spent pursuing animals or setting traps, to calculate catch per unit effort (CPUE), we used catch per hunter per day (CPHD) to document hunter returns. We then used the changes in the mean body mass indicator (MBMI) throughout the study period to test for defaunation in the three villages. Differences in CPHD and MBMI by month and year, between villages and hunting method, were investigated using Tweedie regression models. For all species pooled, we found that the mean CPHD remained relatively constant between 2003 and 2016. There was an observed shift from traps to firearms during the study period. CPHD for each of the seven most hunted species did not vary significantly during the entire study period, and a similar change from traps to firearms was observed. MBMI also remained stable for all species pooled, but significantly declined in the remotest village. Starting MBMI values for this village were higher than for the other two settlements perhaps because wildlife here is less depleted. Although hunter effort data may be difficult to obtain over long time periods, CPHD and MBMI may be useful tools as a measure of impact of hunters on prey populations

Modelling the covariance structure in marginal multivariate count models: Hunting in Bioko Island.

The main goal of this article is to present a flexible statistical modelling framework to deal with multivariate count data along with longitudinal and repeated measures structures. The covariance structure for each response variable is defined in terms of a covariance link function combined with a matrix linear predictor involving known matrices. In order to specify the joint covariance matrix for the multivariate response vector, the generalized Kronecker product is employed. We take into account the count nature of the data by means of the power dispersion function associated with the Poisson–Tweedie distribution. Furthermore, the score information criterion is extended for selecting the components of the matrix linear predictor. We analyse a data set consisting of prey animals (the main hunted species, the blue duiker Philantomba monticola and other taxa) shot or snared for bushmeat by 52 commercial hunters over a 33-month period in Pico Basilé, Bioko Island, Equatorial Guinea. By taking into account the severely unbalanced repeated measures and longitudinal structures induced by the hunters and a set of potential covariates (which in turn affect the mean and covariance structures), our method can be used to indicate whether there was statistical evidence of a decline in blue duikers and other species hunted during the study period. Determining whether observed drops in the number of animals hunted are indeed true is crucial to assess whether species depletion effects are taking place in exploited areas anywhere in the world. We suggest that our method can be used to more accurately understand the trajectories of animals hunted for commercial or subsistence purposes and establish clear policies to ensure sustainable hunting practices