Thirty years of changes in the decapod community from the deep-water fishing grounds off Kueishan Island, Taiwan

Abstract

The deep water off Kueishan Island, NE Taiwan, is a traditional fishing ground for the deep-water fishing vessels based at Dasi fishing port. Since the opening of the deep-water fishing ports at Dasi in the late 1960s, the fishing grounds off Kueishan Island have been continuously trawled, for over 50 years now. The present study compares the decapod assemblages in the catches of Dasi fishing port among four periods of time, spanning more than 30 years, namely, 1981-1990, 1991-2000, 2001-2010, 2011-2012. A total of 66 families, 203 genera and 420 species of decapod crustaceans have thus been recorded in the catches landed at Dasi fishing port from 1981 to 2012. During 1981-1990, 202 species were recorded, followed by 262 species from 1991-2000, 236 species from 2001-2010, and 265 species from 2011-2012. In all four periods, crabs (Brachyura) were the largest group, representing more than 30%, followed by Dendrobranchiata. Comparing the species composition among the four periods, each period contains a group of species exclusively found at that particular period of time. There were 26 exclusive species in 1981-1990, 49 in 1991-2000, 21 in 2001-2010 and 50 in 2011-2012. On the other hand, there are 94 species common to all four periods. Trajectory plots in the nMDS ordinations shows a gradual directional change in species composition from 1981-1990 to 1991-2000, 2001-2010 and 2011-2012. Since each consecutive period has a higher similarity with the previous than with the other periods, this suggests that the observed trend is not a random pattern. The decapod community in the waters off Kueishan Island has a very high diversity, but the species composition is unstable over time and also changing with time. Under the locally prevailing circumstances, we hypothesize this likely is a succession process in response to the continuous disturbance from the trawl fisheries.