Country Paper 9: A science-based management approach for sustainable mariculture in Hong Kong SAR

In Hong Kong SAR, marine finfish culture is mainly carried out in cages suspended by floating rafts in designated coastal waters, named fish culture zones (FCZs). These zones are mostly located in semi-enclosed and weakly flushed coastal tidal inlets that provide shelter against typhoons and waves. This paper describes the successful application of WATERMAN – a science-based fisheries management system – for sustainable development of mariculture in Hong Kong SAR. The WATERMAN system is based on a unique integration of mathematical modelling and field studies, and provides quantitative determination of the carrying capacity of existing and potential FCZs in Hong Kong SAR. The system accounts for factors that include tidal flushing, pollution loading from fishfarms, phytoplankton dynamics and nutrient recycle, sediment-water interactions, and statutory water quality objectives; it also caters for different seasonal and environmental scenarios. Using WATERMAN, we determined the carrying capacity of all the existing FCZs in Hong Kong SAR. Based on the findings and taking into consideration other factors, the Agriculture, Fisheries and Conservation Department (AFCD) recently launched a pilot scheme to issue new marine fish culture licences for fishermen to practice mariculture in three FCZs having surplus carrying capacity. The WATERMAN system also identified some overloaded FCZs, suggesting a need to reduce the stocking volume and/or increase the culture area. The AFCD, therefore, plans to expand one overcrowded FCZ by rearranging and spreading out the existing rafts within the expanded zone to improve the culture environment. The WATERMAN system is also used to help identify potential new sites for fish farming, thereby strengthening the sustainable development of mariculture in Hong Kong SAR.