title: Optimising the fishery of the under-exploited edible sea urchin, Centrostephanus rodgersii
Creators: name: Campus, P
Publisher: name: University of Tasmania
Year: 2022

description: Climate change in the Southern Ocean is posing problems in many coastal areas where changes in ocean currents affect dispersal, water temperature and nutrients so that the ecological balance of the rocky reefs is adjusted. Although changes have occurred in the past as a normal part of marine ecosystems, the current rapid rate of change introduces special challenges. Research on the negative effects of climate change on marine ecosystems is most common, although the arrival of new species through range extension can also be positive where this brings new commercial opportunity. The overall objective of this thesis was to guide the development of best practices to optimise the emerging commercial fishery of the range extending edible sea urchin, Centrostephanus rodgersii. By optimising the fishery, a cost-effective method can be developed to combat the climate-driven negative impacts of C. rodgersii, which include the formation of extensive urchin barrens and subsequent negative impacts on lucrative traditional fisheries. The objective was achieved via pre-harvest investigations into the natural influences on gonad biochemistry as well as roe enhancement opportunities, and post-harvest research on handling stress and waste utilisation. Economic returns in urchin roe fisheries are highly dependent on roe quality, with 10-fold increases in value from low to high-quality roe based on macroscopic characteristics. As such even small advancements in fishery processes can lead to large economic rewards. In Chapter 2, the effect of seasonality, feeding habitat and sex on urchin gonad physical parameters and biochemical composition is described. In this study, C. rodgersii showed a pattern of gonad growth and biochemical composition similar to other echinoids, while only minor differences were found between gonad of animals from kelp bed and barrens habitat. Protein was the main gonad macronutrient followed by lipids, with males being higher in proteins and females in lipids. Triacylglycerol was the main class of lipids in both sexes. No differences in gonad colour were found between urchins in kelp and barrens while it was observed a higher accumulation of lipids in urchins feeding in kelp areas compared to the barren ones. Gonad of both sexes had good texture and firmness between September and June during recovery and maturation, while were softer and difficult to handle and process at the spawning stage. It has long been held that urchins from barrens habitat have poor roe quality and should be avoided by urchin fishers, whereas I was able to demonstrate that urchins living in barrens possess not only gonad of acceptable commercial yield but also good fatty acids and amino acids profile. Urchins living in the barrens represent an unfished stock available to be targeted by the fishery which by doing so would alleviate the urchins fishing pressure on the kelp beds while at the same time reducing the urchins’ population density in the barrens allowing the recovery of algae cover. In Chapter 3 an experimental feeding trial was undertaken to examine the potential for supplementary feeding to enhance the quality of C. rodgersii gonad. Growth of gonad in urchins provided with the formulated feed pellets was similar to growth of a wild control, whereas there was little growth of urchin gonad in the fresh algae diet treatments. There was however a pattern of accumulation in biochemical components from the algae to the gonad. These preliminary results show that gonad yield enhancement through urchin farming is at the moment unnecessary given the large availability of urchins with good yield along the Tasmanian eastern coast in both barrens and kelp habitats. However, it provides a starting point for further studies aimed at improving the quality aspects of the gonad, namely colour, texture and flavour. Specifically, results showed a selective accumulation of sweet taste amino acids in gonad of urchins fed the algae Ulva spp. Further development should be addressed in gonad sweet and umami taste enhancement in short time aiming at the production of high-priced A-grade roes. In Chapter 4, the effect of post-harvest handling techniques on urchin stress was explored by a simulated harvest and post-harvest storage experiment that mimicked current harvest practice in the commercial fishery. Live urchins collected during the fishing season with mature gonad were exposed to different environmental conditions to investigate the effect of air exposure and storage during fishing, as well as storage post-fishing, on gonad quality prior to processing. High temperature, wind and storage time were shown to increase stress and premature death of animals, as did storage at low temperatures. Protecting the urchins from direct wind and sunlight, storing them at ambient seawater temperature and minimising shell damage reduced stress and mortality and preserved gonad quality. Centrostephanus rodgersii survival after the harvesting is greatly determined by air exposure, storage conditions and time prior to processing. The results show that optimising post-harvest handling techniques can vastly improve roe quality and economic returns. Both fishers and processors should employ practices aimed at reducing stress and mortality from the moment of harvesting to the moment of processing with the ultimate goal of preserving maximum freshness and gonad quality. In Chapter 5 the waste of sea urchin processing was analysed for its nutrient content and applied as an organic fertiliser in an experimental growth trial with greenhouse tomato plants. Dried urchin shell powder at the highest rate of addition produced vegetative growth comparable to a control fertiliser solution but resulted in only half of the fruit production due to macronutrient exhaustion. Results show the urchin waste product has a distinct profile of both macro and micronutrients with high bioavailability for uptake by plants, indicating potential commercial development. The fertiliser trial demonstrated that urchin waste, which is the majority of biomass landed, has the potential to be used as an organic soil ameliorant and plant fertiliser. In doing so it will reduce the environmental impact and costs of waste disposal while simultaneously promoting the economic viability of the urchin fishery and maximising the economic return creating economic value of the waste product. This thesis provides some clear directions for changes in current fishery practice and provides also a clear direction for further research on maximising roe quality and utilisation of urchin waste products. Utilising the key findings of this thesis the commercial C. rodgersii harvest fishery will be able to be optimised with increased profitability. Collecting urchins from barrens habitat would reduce the population density and therefore reduce the grazing pressure on the rocky reef allowing the recovery of algae cover. The recovery of the Tasmanian rocky reef would benefit the ecosystem and other compartments of the fishery like Abalone and rock lobsters. A better understanding of C. rodgersii population dynamic related to gonad quality will improve the management of the resource and the urchin fishery in the long term