Consequences of past and present harvest management in a declining flyway population of common eiders Somateria mollissima

• Published in: Ecology and evolution Vol. 9; no. 22; pp. 12515 - 12530
• Main Authors: Tjørnløv, Rune S., Pradel, Roger, Choquet, Rémi, Christensen, Thomas Kjær, Frederiksen, Morten
• Format: Journal Article
• Language: English
• Published: Bognor Regis John Wiley & Sons, Inc 01.11.2019; Wiley Open Access; John Wiley and Sons Inc; Wiley
• Subjects: Adaptive management; Adults; Animal biology; Biodiversity and Ecology; Bird migration; CMR modeling; Computer simulation; Death & dying; demography; Environmental Sciences; Females; Hunting; hunting bag statistics; Life Sciences; Males; Management; Mortality; multi‐event model; Original Research; Overexploitation; Population decline; Population dynamics; Population number; prospective population scenario; sex ratio; Simulation; Somateria mollissima; Stochasticity; Time series; Trends; Vertebrate Zoology; Denmark; Wadden Sea; Europe; Baltic Sea; prospective population scenarios; multi-event model; demography; hunting bag statistics; CMR modelling; population dynamics; sex ratio
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.5707

Harvested species population dynamics are shaped by the relative contribution of natural and harvest mortality. Natural mortality is usually not under management control, so managers must continuously adjust harvest rates to prevent overexploitation. Ideally, this requires regular assessment of the contribution of harvest to total mortality and how this affects population dynamics. To assess the impact of hunting mortality on the dynamics of the rapidly declining Baltic/Wadden Sea population of common eiders Somateria mollissima, we first estimated vital rates of ten study colonies over the period 1970–2015. By means of a multi‐event capture–recovery model, we then used the cause of death of recovered individuals to estimate proportions of adult females that died due to hunting or other causes. Finally, we adopted a stochastic matrix population modeling approach based on simulations to investigate the effect of past and present harvest regulations on changes in flyway population size and composition. Results showed that even the complete ban on shooting females implemented in 2014 in Denmark, where most hunting takes place, was not enough to stop the population decline given current levels of natural female mortality. Despite continued hunting of males, our predictions suggest that the proportion of females will continue to decline unless natural mortality of the females is reduced. Although levels of natural mortality must decrease to halt the decline of this population, we advocate that the current hunting ban on females is maintained while further investigations of factors causing increased levels of natural mortality among females are undertaken. Synthesis and applications. At the flyway scale, continuous and accurate estimates of vital rates and the relative contribution of harvest versus other mortality causes are increasingly important as the population effect of adjusting harvest rates is most effectively evaluated within a model‐based adaptive management framework. We used multi‐event and stochastic population modeling to assess the past and present effect of hunting in a declining flyway population of common eiders. Our results indicate that even a ban on shooting female eiders is not enough to halt the current decline, because of high levels of natural mortality among the eider females.