Katie Cresswell
Longspined sea urchins, Centrostephanus rodgersii, arrived in Tasmania due to a climate-driven range-expansion, triggering concern due to their tendency to graze destructively at high densities, creating “urchin barrens” of bare rock, destroying kelp forest, and negatively impacting other fisheries. The arrival of the species also sparked a commercial fishery that began in 2009, expanding to become one of the state’s largest wild fisheries, and has been partly subsidised by the government to target areas of importance. Both the creation of a successful fishery and its use as a tool to manage a problematic species are key examples of human adaption to climate change, however the impact of the fishery on its stock has so far been difficult to determine. We created a size structured stock assessment model to represent the range-extension of urchins to Tasmania, finding that the fishery has had a large impact in the region of highest urchin recruitment, where we predict urchin density would be almost doubled if no commercial fishing had occurred. For each region, we explore projections of harvest intensity and filter this by potential reef productivity to provide a framework for possible management goals, indicating regions where an ecological density target could be obtained through fishing, or regions where intervention would likely be unnecessary depending on the goal. Our approach provides quantitative support for managing and adapting to a problematic new species in a temperate reef by using existing tools and data, exploring the limits and effectiveness of these tools in different areas.
Presentation Slides – Katie Cresswell
