Monitoring abalone juvenile abundance following removal of Centrostephanus and translocation
Waste to profit in urchin fisheries: developing business opportunities to ensure fishery sustainability and safeguard reef dependent fisheries from destructive urchin grazing
Increasing the viability of urchin fisheries is particularly important for the range-extending Centrostephanus rodgersii which is threatening the productivity and profitability of the lucrative abalone and rock lobster fishing grounds as far south as the Tasman Peninsula (south-eastern Tasmania). Waste products from urchin fisheries account for over 85% of the harvested biomass, with up to 180 tonnes of sea urchin waste produced annually. Developing saleable by-products from waste will increase the viability and profitability of urchin fisheries by 1) creating new business opportunities 2) reducing waste disposal and transport costs and 3) enabling increased harvest levels temporally (longer seasons), spatially (further from port) and at an increased density.
Cost effective control of Centrostephanus is a key priority of the Tasmanian Government as well as the Tasmanian Abalone and Rock Lobster Council. Similarly, the State Government of Victoria and the Eastern Zone Abalone Industry Association have highlighted the need to control the destructive overgrazing of urchins. A profitable Centrostephanus fishery is seen as the best way to achieve this. However, profitability in the fishery is currently low given the species lower average roe quality. Methods to reduce costs and increase profitability are vital for a prosperous fishery and control of destructive urchin grazing.
Processors, encouraged by initial trials and results, believe there is a high potential to develop a commercial product from the waste. However, cost and lack of expertise have impeded the timely development of waste-derived products within industry.
Final report
Can commercial harvest of long-spined sea urchins reduce the impact of urchin grazing on abalone and lobster fisheries?
Tactical Research Fund: trial of an industry implemented, spatially discrete eradication/control program for Centrostephanus rodgersii in Tasmania
Sponsorship of 13th International Echinoderm Conference
The conference theme - Echinoderms in a Changing World - focuses on major current issues including climate change and ocean acidification, as well as incorporating echinoderm physiology, biogeography, genetics, genomes and development as major focal points in marine research. Tasmania is a highly appropriate location given international attention to the circumstances of climate change driving range extension of an echinoderm into Tasmanian waters, where it poses a significant threat to biodiversity of shallow rocky reef systems and the sustainability of associated fisheries.
Rebuilding Ecosystem Resilience: assessment of management options to minimise formation of ‘barrens’ habitat by the long-spined sea urchin (Centrostephanus rodgersii) in Tasmania
There is clearly potential for C. rodgersii barrens to cover ~50% of nearshore reefs on the east coast of Tasmania, as is already the case in NSW and the Kent Group in Bass Strait. This would reduce both the Tasmanian abalone and rock lobster fisheries by ~15%, with a loss of value totalling ~$25M (before processing). The need for a management response is self evident.
Large rock lobsters (=135 mm CL) are the key predators of C. rodgersii in Tasmania, and experiments have shown clearly they can prevent sea urchin populations from building to the point where overgrazing occurs. There is urgent need to assess the viability of controlling C. rodgersii populations through changing current management of the rock lobster fishery, and through targeted removal by divers as a tactical response on small scales.
However, before management instruments are invoked in an attempt to minimise the risk of further development of barrens habitat or rehabilitate existing barrens, it is imperative to carefully evaluate the effectiveness of potential management strategies. The proposed research will provide the necessary information and knowledge base to enable robust management decisions.
The proposed work has strong support from managers and the fishing industry in Tasmania, is acknowledged as a high priority by the relevant RAGs, and addresses several high priorities on both the State and TAFI strategic research plans.
Final report
By overgrazing seaweeds and sessile invertebrates, essentially back to bare rock, the advent of the long‐spined sea urchin Centrostephanus rodgersii in eastern Tasmanian waters poses a significant threat to the integrity, productivity and biodiversity of shallow (<40 m) rocky reef systems and the valuable fisheries (principally abalone and rock lobster) that they support. The present research examined means of managing this threat at small, medium and large spatial scales.
Divers have the opportunity to limit C. rodgersii densities at local scales by culling or harvesting to prevent formation or expansion of urchins ‘barrens’ habitat at incipient stages when barrens occur as small patches in seaweed beds. To ensure sufficient time for seaweed recovery in cleared patches, local control in this way requires that sea urchins show a high fidelity to their particular incipient barrens patch so that once a patch is cleared of sea urchins there is little likelihood of it being quickly recolonised by other individuals from nearby patches. We found that on all types of barrens habitat C. rodgersii is highly nocturnal in behaviour, and has a strong tendency to return to its home crevice at the end of each night. Individuals in incipient barrens patches show strong fidelity to their patch over periods of several months, with little tendency to cross the boundary between barrens and seaweed cover, such that mean net movement in small patches is less than 1 m in 3 months. Accordingly, there is little tendency to migrate among patches, which is explained in part by laboratory experiments indicating that C. rodgersii lacks a directional chemosensory response to either macroalgae or conspecifics. Thus, urchin behaviour suggests that localised culling is likely to be effective in rehabilitating existing incipient barrens patches and reducing risk of further patches forming.
However, this outcome is unlikely to be achieved by the activity of professional divers culling urchins while fishing for abalone. Our trials indicate that abalone divers are motivated primarily by catching abalone. Thus, while they can be effective at culling urchins from the individual incipient barrens patches they encounter so that seaweeds recover in these particular patches, the number of patches they are able to visit while fishing through an area is small so that the overall effect of their culling activity within the area that they fish is not detectable except at the scale of individual patches visited. Given typical revisitation times to fish in a given area, divers culling urchins while fishing abalone are unlikely to provide meaningful local control of urchin populations. In this context, systematic and targeted harvesting of urchins as an independent industry, or killing urchins with quicklime or by deploying divers whose sole task is to cull urchins, is likely to be much more effective (but at added cost).
Abalone divers culling C. rodgersii while fishing can be successful in helping to regenerate seaweed cover on particular targeted barrens patches, but this is unlikely to have any significant effect in controlling urchins at the level of dive sites or reefs. Abalone divers should be encouraged to cull C. rodgersii while fishing.
Keywords: Sea urchin, Centrostephanus rodgersii, rock lobster, Jasus edwardsii, abalone, Haliotis rubra, sea urchin barrens habitat, ecosystem based management, modelling, stock rebuilding, maximum economic yield.