Wetland conservation and sustainable use under global change: a tropical Australian case study using magpie geese

Abstract

Imminent shifts in environmental parameters due to climatic change might have profound ramifications for wetlands listed under the Ramsar convention. Although the exact mechanisms by which global change will affect these systems are not known, models that simulate component drivers, particularly at a broad spatial scale, can nevertheless allow for more informed conservation decision making. Such general inference is particularly needed for wetlands across the tropics, where less knowledge and fewer resources are available to mitigate the impacts on important conservation sites. Here we develop a case study of wetland loss to sea level rise across tropical north Australia (including Ramsar-listed sites), and link these to a metapopulation model for a keystone endemic waterbird, the magpie goose Anseranas semipalmata. We projected published models on sea level rise through to the year 2400, and found a non-linear trajectory of inundation up to 20 m above present levels. Digital elevation models were used to simulate sea level rise and the spatially differentiated loss of wetland habitat used by geese. Range retraction was linked to decline in ecological carrying capacity, and we coupled wetland-specific habitat loss projections to a spatially explicit demographic metapopulation model. Additionally, we included alternate harvest strategies based on present-day estimates of indigenous and non-indigenous offtake of geese, and examined the synergy between wetland loss and hunting on extinction risk. Our results suggest that Australia’s onceabundant and widespread magpie goose will be reduced to a fragmented population of just a few thousand individuals within the next 200-300 yr. Harvest could continue for some time, up to a "tipping point" at around 5% loss of current wetland habitat, after which the decline of geese is rapid. Given the inexorable nature of sea level rise, short- to mediumterm conservation of waterbirds across Ramsar wetlands must prepare for adaptive wetland management, such as through buffer-placement, and ongoing monitoring of harvest.