Barren-ground caribou - a cyclic species: The development of a cycle-stratified harvest model and a cycle analysis of North American barren-ground caribou subpopulations

Abstract

Unlike all other members of the deer family, subpopulations of barren-ground caribou (Rangifer tarandus groenlandicus) exhibit fluctuations in numbers that have been described as cyclic. We created a cyclic individual-based annual life table harvest model to examine the sustainability and user-benefits of regulating the harvest during the portion of the cycle characterized by low numbers, low unharvested population growth rates, or both for the Qamanirjuaq caribou subpopulation (Chapter 1). Cyclic population dynamics were modeled using density-driven dynamic responses of both per capita survival and calf production to a cyclic carrying capacity function. Model parameters were empirically identified to produce cycles that replicated observed Qamanirjuaq (Nunavut, Canada) subpopulation dynamics, including changes in population numbers, human harvest, calf production and calf survival rates. We modified the cyclic barren-ground caribou harvest model, developed for the Qamanirjuaq caribou subpopulation, to model the Bathurst and George River subpopulations. We were able to develop models that corresponded to time-series field estimates of population numbers, calf production rates, and calf survival rates of the Bathurst and George River subpopulations, suggesting that the structure of program CARIBOU 1.0 general and robust. We identified three harvest options for the Qamanirjuaq, Bathurst and George River subpopulations: 1) maximized the total number of removals per cycle, 2) minimized the number of years with imposed restrictions, and 3) minimized the degree and frequency of differences between strata harvests (maximized “evenness”). The range of sustainable harvest options was large for all three subpopulations, and thus offers a framework to exploring harvest strategy options in consultations and co-management planning. Deliberate reduction of harvest during the decline and early increase phases of the cycle significantly reduced the period when subpopulations were too small or increasing too slowly to sustain a harvest at basic needs levels.