Biomass and distribution of carangoid fish resources in the offshore South China Sea

In order to identify the biomass and distribution of carangoid fish resources in the offshore South China Sea, four acoustical surveys were conducted using scientific echosounder (Simrad EY60) with light falling-net fishing in the middle south area (6N～17N) of the open South China Sea (autumn2012, spring 2013) and north area (17N～22N) of the offshore South China Sea (spring 2015, autumn 2015). On the basis of determining the effectiveness of the method, the survey results showthat the biomass of carangoid fish resources was 4.13105 t and 3.49105 t in the south-central area in autumn2012 and in spring 2013, and the high density area were both 15N transect. In the north area, the biomass of carangoid fish resources was 2.03105 t in spring 2015 and the high density area was 18.50N～19.50N, 113.00E ～116.00E, but that biomass was only 0.59 105 t in autumn 2015. The species composition of carangoid fish presented significant seasonal difference, and Decapterus macarellus and D. macrosoma were the most important economic carangoid species; the biomass density of carangoid fish resources in the south-central area in autumn 2012 was significantly higher than that in the north area in autumn 2015 (P0.01, t-test) , butwas not significantly different with that in spring 2013 (P0.05, t-test) ; the difference of the biomass density was not significant between the south-central area in spring 2013 and the north area in spring2015 (P0.05, t-test) , but the biomass density in the north area in spring 2015 was significantly higher than that in autumn 2015 (P0.01, t-test) .