Abstracts

Presented by Thomas Riecke - Email: triecke@cabnr.unr.edu

Recent and previous research has addressed density-dependent effects on population growth rates of North American waterfowl populations. Critically, current management frameworks result in harvest regulations tracking the abundance of North American waterfowl species. Consequently, harvest is increased when the potential for density-dependent effects are high. Previous work showed that this relationship may confound our understanding of the effects of harvest on mortality. We use novel hierarchical approaches to directly examine these relationships in blue-winged teal (Spatula discors), an abundant North American dabbling duck. Our results indicate that minimal ( 0.02) changes in harvest rate paradoxically appear to have strong (> 0.15) impacts on survival rates of adult female blue-winged teal if other causal mechanisms are not considered. Survival rates of all age and sex classes decline dramatically following minor increases in harvest rate, and major increases in abundance. Process correlations () among harvest and natural mortality rates of adults appears to be additive or depensatory for both adult females (= 0.232, 95% CRI -0.055 0.440) and adult males ( = 0.193, 95% CRI -0.114 0.461). However, we note that large increases in teal abundance were strongly correlated with natural mortality rates for adult females ( = 0.565, 95% CRI 0.273 0.807), adult males ( = 0.401, 95% CRI 0.094 0.663), juvenile females ( = 0.599, 95% CRI 0.310 0.839), and juvenile males ( = 0.565, 95% CRI 0.273 0.807), despite minor variation in harvest, putatively leading to the observed major changes in survival. These results indicate that it is critically important to consider multi-dimensional relationships among harvest, natural mortality, and abundance when assessing the effects of harvest on population growth rates. These findings have important implications for the management of populations of harvested species.