Annual variation in fish biomass size spectrum in Daya Bay, South China Sea in summer

Based on the data collected from three bottom trawl surveys of fishery resources in 2015, 2017 and 2018, we constructed the biomass size spectrum of fish in the Daya Bay in summer, and compared and analyzed the differences of the characteristic parameters of fish biomass size spectrum. The results show that the biomass size spectrum in different years displayed obvious annual and spatial variation characteristics. The fish biomass size spectrum of the Sheldon-type were all "single-peak" as a whole, with the largest particle size ranges in 2015 and 2018 (−1–9), followed by 2017 (−1–8); The dominant species composition of the fish community evolved from Thamnaconus hypargyreus, Leiognathus brevirostris and Apogon lineatusin in 2015 to the main small-size species such as L. brevirostris and Siganus oramin in 2017 and 2018. The species composition of the normalized biomass size spectrum curvature in 2015 was the largest, followed by that in 2018, while that in 2017 was the smallest. In terms of spatial distribution, the curvature of the coastal waters was the largest in 2015 but the smallest in 2017; the curvature of the central area was the largest in 2018 but the smallest in 2017; and the curvature of the mouth area was the largest in 2018 but the smallest in 2017. The abundance-biomass comparison (ABC) curve indicates that the fish community in the Daya Bay in summer was at a state of severe disturbance. The biomass size spectrum characteristics displayed obvious annual differences, relating to fish life habits, supplement ratios, habitat environment and human activities, especially fishing factors.