A feasibility study on pearl oyster cultivation in mariculture zones in Hong Kong

Abstract

Pearling is part of Hong Kong's marine heritage. The colonial government supported the establishment of the pearl oyster culture industry in the 1950s. However, the attempts failed. Hong Kong is an international trading hub of pearls today. The jewellery industry contributed 20.7% of the total domestic exports in 2019. At the same time, there are many idle fish rafts in mariculture zones because it is not profitable for the fishers to engage in fish farming. This study aims to investigate the feasibility and economic potential of using these fish rafts for cultivation of pearl oysters. Through historical analysis, this study identified the reasons for the failure to build the industry in the past and found that most of these problems no longer exist now. At present, the fishers are interested in pearl oyster farming and have received funds to start pearl oyster culture. Experiments were carried out in six different mariculture zones to study if the extreme environmental conditions and biofouling situation in these zones are suitable for pearl oyster culture. The results showed that pearl oysters' growth rate and survival rate in Sai Kung north were higher than in Tolo Harbour. It was found that extremely low dissolved oxygen (DO) and extremely high suspended solids level negatively affected the growth rate, but higher turbidity level promoted the growth rate of the pearl oyster. High extreme temperature and turbidity level, extremely low DO and salinity, and a higher biofouling growth rate would increase the mortality of the pearl oyster. Attempts were made to increase the cost-effectiveness of pearl oyster farming. Experiments were carried out using a low-voltage electric current with an aim to promote the growth of pearl oysters but failed. Nonetheless, field trials in the present study demonstrated that immersion of the culture nets and pearl oysters in freshwater regularly was a cost-effective way to control the biofouling. This method can reduce a lot of the operating costs of the farm. Other than the income from the pearl, oyster meat has been available in the seafood market. In addition, the pearl powder from the shell is used in Traditional Chinese medicine (TMC) and is an ingredient for cosmetics. Therefore, every part of the pearl oyster has economic value. As revealed by simulation and comparison among different business models, a farm that cultures pearl oyster only for oyster meat and shell powder would be the most profitable business model in terms of the net present values (NPV) and internal rate of return, IRR. The payback period of this business model was also the shortest. Therefore, it is feasible and profitable to use the idle fish rafts in mariculture zones for pearl oyster culture. It is recommended that the government should support the pearl oyster culture business because of its positive externalities, such as its ecosystem services and potential benefits to other industries.