Changes in the fish species composition in the coastal zones of the Kuroshio Current and China Coastal Current during periods of climate change: Observations from the set-net fishery (1993–2011)

Changes in fish distribution and migration patterns have occurred in mid- and high-latitude oceans worldwide in response to climate change. Since the 1980s, the sea surface temperature (SST) of the southern East China Sea has increased significantly, particularly in winter. The mechanisms behind these changes in migratory fish assemblages are difficult to elucidate from general capture fisheries databases. This study collected a long-term data set of set-net catches, reported from the remote Tung-Ao Bay in northeastern Taiwan to analyze catch composition. Both the total number of species and the Shannon–Wiener index (H′) showed an increasing trend, while the cumulative percentages of the top 10 captured fish species decreased annually. These results indicated that in the coastal zone at the front of Kuroshio Current (KC) and China Coastal Current (CCC), increased SST caused fluctuations in the presence of cold-water and warm-water fishes and in the timing of fishing seasons. Additionally, results based on multidimensional scaling (MDS) and cluster analyses showed that the study period could be divided into two clusters, 1993–1997 and 1998–2011, with an 80% similarity value. The boundary of these clusters was consistent with changes in SST. A species composition change analysis of these clusters showed that clustering was associated with changes in the intensities of the CCC and KC, especially in winter seasons. A northward expansion of low-latitude fish species was observed in Tung-Ao Bay, similar to expansion of high-latitude fish species into Polar region.