Subsidizing the overharvest of an overgrazing, range-extending sea urchin for kelp restoration and abalone habitat protection

The commercial harvest of the range-extending longspined sea urchin (Centrostephanus rodgersii) in Tasmania, Australia, was rapidly accelerated by catch subsidies initiated by the abalone industry, which it threatened. The 650 km climate-driven extension of the urchin distribution, and subsequent extensive overgrazing of kelp reef ecosystems, represents one of the largest and most immediate threats to the USD 52 million abalone industry. This threat also extends to hundreds of kelp-associated species, and in turn results in the downgrading of social, cultural, ecological and economic values. The response of the abalone industry – to both initiate subsidy payments for urchin removals and to lobby for political support – was fundamental to securing timely and effective management intervention on this locally non-indigenous species (NIS). Harvest subsidies provided the urchin industry with financial reassurance to overcome barriers associated with infrastructure, intellectual knowledge on urchin processing, and international market development. After a decade of urchin industry fluctuations pre-subsidy, harvests of urchins quickly rose to 500 tonnes per annum after its inception, resulting in extensive kelp protection and localized kelp restoration in areas of intense urchin fishing. The early
action to prevent extensive urchin overgrazing along the 250 km Tasmanian east coast has been both effective and affordable, as rehabilitating hyper-stable, extensive barren grounds would inevitably involve substantially higher effort and cost. Financial support from the Tasmanian State Government and the introduction of spatially variable harvest subsidies has seen the urchin control redistributed to regions of high importance for the abalone industry. Additional urchin control actions, such as “take-all” (all urchin size classes) harvesting and culling, have been trialled to supplement the commercial harvest, further reducing urchin abundances on high-value reefs. Marine spatial planning and associated decision tools are under construction to facilitate spatial prioritization of harvesting, subsidy allocation, and control method application. Here we document that with support and prioritization, commercial harvest can be an affordable and effective management strategy of aquatic NIS over large scales.