Tactical Research Fund: trial of an industry implemented, spatially discrete eradication/control program for Centrostephanus rodgersii in Tasmania
University of Tasmania (UTAS)
Over the last three decades the distribution of long-spined sea urchin has extended from its native range in NSW down the east coast of Tasmania and west through Victoria. The impact of this range expansion is expected to intensify. This large sea urchin overgrazes seaweeds and invertebrates on rocky reefs, causing catastrophic regime shifts in the coastal ecosystems. The 'barren' habitats that are left after the establishment of an urchin population are unable to support commercial or recreational fisheries for abalone or rock lobster among other species. Therefore the incursion of this species into non-endemic regions pose a significant threat to the integrity of shallow reef ecosystems and the associated biodiversity and fisheries these regions support.
1. Determine the effectiveness of divers physically destroying urchins in situ to either eradicate or control spatially discrete aggregations to allow the re-establishment of native flora and fauna
2. Determine the cost effectiveness of objective 1 in regard to lost production for commercial, recreational and customary harvests.
The cost of manually controlling an invasive species in the marine environment is inherently expensive due to the costs associated with mobilising logistics to a target area, and secondly the limitations of diver time in the water. In this report we present models that can be used to generate cost estimates to cull a given area based on urchin density and dive depth, with the maximum depth chosen having a great effect on the overall cost. A local scale model estimates the maximum cost to cull Wineglass Bay to a depth of 20 m at $1,617,802, based on a constant density estimate of 1.5 urchins.m‐2. The cost to cull reef areas within Fortescue Bay to a maximum of 20 m using the same model at $877,019 based on a constant density of 0.29 urchins.m-2.
This report shows that systematic culling can significantly reduce the density of C. rodgersii in discrete areas. The implications of these findings are that culling can be considered a viable method in the management strategy evaluation of controlling the deleterious effects of C. rodgersii. The costing models provide tools to estimate the direct cost of implementing a culling strategy at a range of spatial scales across the east coast and can be manipulated to provide a bio-geographically accurate estimate of cost depending on the area (and size of area) selected.Keywords: Invasive species, non-‐indigenous species, regime shift, phase shift, climate change, range expansion, temperate rocky reefs, kelp beds, sea urchin barrens, grazing, culling, population expansion control