Monthly Variability In The Catchability Of Chub Macherel And Round Scad And Its Relationship With Environmental Seasonality In The Southern Taiwan Strait

In order to understand the fluctuations in marine fish stocks, which is important for the management of fisheries, numerous attempts have been made to demonstrate links of fish stock fluctuations with oceanographic and climatic variability. Less attention has been paid to the coastal sea. Taiwan Strait, a shallow channel linking the East China Sea with the South China Sea, is one of the main fishing grounds in China. As a first step to address the responses of fish stocks to the oceanographic variability, the monthly and spatial patterns of Chub Macherel and Round Scad fishery in relation to oceanographic measures such as Sea Surface Temperature (SST) and Chlorophyll a (Chla) for the southern Taiwan Strait (STWS) are analyzed for the period 1986 ~ 2002.In this study we use logbooks of purse-seine fishery during 1986 ~ 2002, AVHRR SST at a 4 km grid during 1986 ~ 2002 and SeaWiFS Chla at a 1 km grid during 1998 ~ 2002 as data availability permitted. Based on this dataset, monthly climatology of catch rates (CPUE), SST and Chla over the STWS are constructed. An areal index of fishing (AI) is obtained by counting grids which have catch rates, and setting weighting factors of 1 ~ 3 to catch rates of less than 1.0 ton/net, equal to or greater than 1.0 ton/net and less than 2.0 ton/net, and equal to or greater than 2.0 ton/net.A strong seasonal pattern of catchability is found for the coastal region off southern Fujian-eastern Guangdong but not in the offshore regions in the vicinity of the Taiwan Bank and Penghu Island. Monthly AI could increase by a factor of up to 10 from winter to summer in the coastal region, while the year-round change is about a factor of 3 in the offshore region. The highest monthly AI (1.10) occurs in August in the coastal region. Nevertheless the highest annual mean AI (0.70) appears in the...