Assessing Compensatory Versus Additive Harvest Mortality: An Example Using Greater Sage‐Grouse

Abstract

We used band‐recovery data from 2 populations of greater sage‐grouse (Centrocercus urophasianus), one in Colorado, USA, and another in Nevada, USA, to examine the relationship between harvest rates and annual survival. We used a Seber parameterization to estimate parameters for both populations. We estimated the process correlation between reporting rate and annual survival using Markov chain Monte Carlo methods implemented in Program MARK. If hunting mortality is additive to other mortality factors, then the process correlation between reporting and survival rates will be negative. Annual survival estimates for adult and juvenile greater sage‐grouse in Nevada were 0.42±0.07 (x̄±SE) for both age classes, whereas estimates of reporting rate were 0.15±0.02 and 0.16±0.03 for the 2 age classes, respectively. For Colorado, average reporting rates were 0.14±0.016, 0.14±0.010, 0.19±0.014, and 0.18±0.014 for adult females, adult males, juvenile females, and juvenile males, respectively. Corresponding mean annual survival estimates were 0.59±0.01, 0.37±0.03, 0.78±0.01, and 0.64±0.03. Estimated process correlation between logit‐transformed reporting and survival rates for greater sage‐grouse in Colorado was ρ = 0.68±0.26, whereas that for Nevada was ρ = 0.04±0.58. We found no support for an additive effect of harvest on survival in either population, although the Nevada study likely had low power. This finding will assist mangers in establishing harvest regulations and otherwise managing greater sage‐grouse populations.

Quantifying risk of overharvest when implementation is uncertain

“…There is an ongoing debate concerning whether tetraonid hunting mortality is compensatory or additive to natural mortality (see e.g. Sandercock et al., ; Sedinger, White, Espinosa, Partee, & Braun, ), although there is at any rate likely to be more compensation at high population densities (Péron, ). Alternatively, managers trust hunters to reduce harvest bags sufficiently with decreasing game abundances.…”

Effects of climatic variation and reproductive trade‐offs vary by measure of reproductive effort in greater sage‐grouse

“…For example, harvest may appear compensatory at the population level, but if ''superior'' individuals are removed disproportionally, effects on population size could be greater than expected. Both additive (e.g., Van Kooten et al 2007, Sedinger et al 2010 and compensatory (e.g., Connelly et al 2000, Gibson et al 2011) harvest mortality have been espoused for sage-grouse. However, harvest mortality hypotheses, as currently conceptualized, may be problematic when reproductively successful groups have differential susceptibility to harvest (Redfield 1975), contribute disproportionately to population growth rates (sensu Taylor et al 2012), and consistently contribute to population growth (i.e., consistently successful ''brood hens''; e.g., Blomberg et al 2013).…”

Northern Pintail (Anas acuta) survival, recovery, and harvest rates derived from 55 years of banding in Prairie Canada, 1960–2014

“…To provide a direct assessment of whether harvest mortality was compensatory or additive to nonharvest mortality, we used Markov chain Monte Carlo (MCMC) methods to estimate process correlations (ρ) between annual survival and recovery rates (Otis and White 2004, Sedinger et al 2010, Arnold et al 2016. Under this approach, if ρ is negative, then harvest mortality can be assumed to be additive and is considered fully additive at ρ ≈ −1.…”

“…Under this approach, if ρ is negative, then harvest mortality can be assumed to be additive and is considered fully additive at ρ ≈ −1. Conversely, harvest mortality is considered fully compensatory at ρ ≈ 0 (Sedinger et al 2010, Arnold et al 2016; ρ² is a measure of the amount of variation in annual survival rates attributable to annual recovery rates. We conducted the MCMC analysis in MARK with the global model S a*s*t , f a*s*t , and prior estimates from this model were used as initial parameter estimates for the analysis.…”