Trends in trawl-targeted species landings off northern Taiwan and effects of fishing and environmental factors

Time series of landings may provide information crucial to achieving a better understanding of temporal variations in the abundances and compositions of exploited species and ecosystems. The waters off northern Taiwan, located in the southern East China Sea, are one of the most important fishing grounds for Taiwan's coastal and neritic fisheries. Temporal variations in the abundances of the species exploited in this region are rarely studied because of the multi-gear fisheries involved. In this study, trends in the landing per unit effort (LPUE) time series for 13 trawl-targeted species (groups) off northern Taiwan from 1976 to 2007 were explored using dynamic factor analysis (DFA). Potential effects of fishing effort (number of vessels) and environmental factors [Southern Oscillation Index, sea surface temperature (SST) near northern Taiwan, and river discharge] were examined. The optimum DFA model included three common trends and three explanatory variables (excluding SST). A general decreasing pattern was identified from among the common trends, and this was observed in the LPUE time series for most of the species. Fishing effort is an important explanatory variable in the model, suggesting that it plays a critical role in explaining LPUE variations of trawl-targeted species. The common trends identified here could lead to new strategies for fisheries management, particularly where multi-gear fisheries operate and multiple species are targeted.