The range-extending Longspined Sea Urchin (Centrostephanus rodgersii) is transforming rocky reefs in eastern Tasmania through overgrazing and formation of extensive urchin barrens, with consequences for kelp ecosystems and valuable abalone fisheries. The Restoration by Harvest program tested whether systematic ‘take-all’ commercial harvesting could functionally eradicate urchins from priority reefs and reduce biomass below the ecological threshold for kelp recovery.
Two harvest phases were undertaken across a 5-km section of coastline at Fortescue Bay between 2023 and 2024. Commercial divers removed all accessible size classes, with diver tracking, underwater visual surveys and towed-video mapping used to quantify harvest effort, urchin biomass, population structure, barren extent and ecosystem response.
The initial coast-wide harvest reduced estimated urchin biomass by 40%, from 56 to 33 t, while a second, smaller harvest twelve months later produced localised improvements that were partially offset by recruitment and growth. Ecological outcomes varied spatially according to the intensity and repetition of harvest. In the Outer region, two successive take-all harvests reduced biomass below the kelp recovery threshold and produced substantial reductions in barren extent, with kelp recovery across all surveyed depth zones. In contrast, biomass in much of the Mid region remained above the recovery threshold despite reductions in urchin abundance, and barrens persisted or expanded.
Size-frequency distributions demonstrated continued population turnover, including growth of urchins surviving the initial harvest and emergence of new juvenile cohorts. This ongoing recruitment highlights the need for repeated intervention to maintain restored reefs below damaging urchin densities.
These results provide proof-of-concept that intensive, spatially targeted take-all harvesting can restore urchin barrens to kelp-dominated reef. However, successful restoration depends on reducing biomass below ecological thresholds and maintaining control through subsequent harvests. Restoration by harvest therefore offers a scalable approach that integrates commercial fishing with active reef restoration and protection of productive abalone habitat.